# A word to the wise on EH 6CA7 tubes!



## MajorNut1967

If you are contemplating using the Electro Harmonix 6CA7 in your older/vintage Marshall, Traynor or with an amp with a negative grid supply; I would stay away from this! The Electro Harmonix 6CA7 is not and I repeat “NOT” a Power Pentode like the original 6CA7’s were, in fact they are Beam Tetrode as stated on the Electro Harmonix website. But the issue is tube venders are saying it is a direct substitute for an EL34 in all situations. Be careful, its not! I you really want to use these tubes in your amps make sure you don’t have a negative grid supply mod or a Traynor Amp. In fact even if your older/vintage Marshall amp has (pin1) & (pin 8) tied to ground, I would stay away from these tubes. 

I found this out on my own. My JCM 800 build project was the test bed, I had told Marty I got a set of Electro Harmonix 6CA7’s to try in it later after the amp broke-in, well I put them in today. I couldn’t get them to bias correctly. So I bumped up he bias voltage up and got them in range, but they amp sounded like crap an the PT was hot as hell. Then friggin Wilder clued me in, after all the bullshit I went through, that it’s not a real power-pentode but a damn Beam Tetrode wannabee. Wilder found it out on Solar’s amps, but didn’t bother to tell me! LOL


----------



## big dooley

> I found this out on my own.





> Then friggin Wilder clued me in, after all the bullshit I went through





> Wilder found it out on Solar’s amps, but didn’t bother to tell me! LOL



?


----------



## Wilder Amplification

MajorNut1967 said:


> If you are contemplating using the Electro Harmonix 6CA7 in your older/vintage Marshall, Traynor or with an amp with a negative grid supply; I would stay away from this! The Electro Harmonix 6CA7 is not and I repeat “NOT” a Power Pentode like the original 6CA7’s were, in fact they are Beam Tetrode as stated on the Electro Harmonix website. But the issue is tube venders are saying it is a direct substitute for an EL34 in all situations. Be careful, its not! I you really want to use these tubes in your amps make sure you don’t have a negative grid supply mod or a Traynor Amp. In fact even if your older/vintage Marshall amp has (pin1) & (pin 8) tied to ground, I would stay away from these tubes.
> 
> I found this out on my own. My JCM 800 build project was the test bed, I had told Marty I got a set of Electro Harmonix 6CA7’s to try in it later after the amp broke-in, well I put them in today. I couldn’t get them to bias correctly. So I bumped up he bias voltage up and got them in range, but they amp sounded like crap an the PT was hot as hell. Then friggin Wilder clued me in, after all the bullshit I went through, that it’s not a real power-pentode but a damn Beam Tetrode wannabee. Wilder found it out on Solar’s amps, but didn’t bother to tell me! LOL



Ah finally...my chance to crap on the Major! 

First off..."negative grid supply"...I thought ALL fixed biased Class AB amps have these! 

To clear up what the Major is saying though...EL34s are a standard pentode. Unlike a beam tetrode, pentodes have a suppressor grid (aka G3 or Grid 3) that is supposed to be either ground referenced or biased with a fixed negative voltage. Some Traynor amps do this and it's supposed to make the EL34s operate more efficiently. The Major implemented this into his JCM800 2203 build.

However, he decided to try a set of EH 6CA7 valves. He learned the hard way that these valves are a beam tetrode in an EL34 bottle. Unlike a regular beam tetrode however, they don't internally connect the beam plates to the cathode and they connect them to pin 1 in place of the suppressor grid that a normal EL34 would have. As such, if you have an EL34 amp that negative biases the suppressor grid, EH 6CA7s do not like this since they are a beam tetrode and not a standard pentode like an EL34. 

Marshall has never implemented this in their designs that I know of. I found out that the EH 6CA7s were beam tetrodes when solarburn sent me his amp just because I happened to notice this. However, on normal Marshalls this isn't an issue since pin 1 is grounded instead of being negative biased like it is in Major's build. On top of that, I had no idea that the Major was going to switch to this valve...had I had known I would've informed him as such.

So bottom line...if you own an amp such as a Traynor that negative biases the suppressor grid pin (pin 1), EH 6CA7s will not work in this type of amp unless the negative bias is removed from pin 1 and pin 1 gets tied to the cathode. EL34s will work with pin 1 tied to the cathode as they have for decades in all Marshalls.


----------



## MartyStrat54

Sorry to hear about that. I feel sort of bad.I told the Major to give them a go. I too knew that they were not wired internally like a real 6CA7, but I didn't know that the Major was going to wire his amp up the way he did.

I'm sorry Major. I hope you didn't burn up your OPT because of it.

Sort of like the Chinese KT88's. They are the same as their 6550, just a different bottle and PN.


----------



## racko7566

Will the EH 6ca7'S harm a dsl 100, or are they ok to use. Mine sounded great with them but the tubes died in like two months.


----------



## Wilder Amplification

racko7566 said:


> Will the EH 6ca7'S harm a dsl 100, or are they ok to use. Mine sounded great with them but the tubes died in like two months.



No...this is why I wish Major hadn't have said anything. Creates an un-needed scare.

Marshall amps have never applied negative bias to the suppressor grid pin on the amps they build for EL34s. They've always connected pin 1 to the cathode (pin 8) on their EL34 amps and as such the 6CA7s will work in any Marshall-made amp that's set up to run EL34s with a cathode referenced suppressor grid pin.

Some of us who build Marshall clones will negative reference the suppressor grid pin as Major did on his and the EH 6CA7s will not work in these amps without converting them to a cathode referenced suppressor grid pin. But not very many of us do this (Traynor is the only other amp maker I can think of that does this and I will soon be doing some experimenting of my own with it) so these amps are the exception to the rule.


----------



## racko7566

Thanks Jon.


----------



## MajorNut1967

MartyStrat54 said:


> Sorry to hear about that. I feel sort of bad.I told the Major to give them a go. I too knew that they were not wired internally like a real 6CA7, but I didn't know that the Major was going to wire his amp up the way he did.
> 
> I'm sorry Major. I hope you didn't burn up your OPT because of it.
> 
> Sort of like the Chinese KT88's. They are the same as their 6550, just a different bottle and PN.



Marty its not your fault at all, I should have researched it more on my own, no worries mate! I tend to always use a negative grid supply on all my EL34 amps mainly because of the crappy CP tubes available. But I think that EH should make the consumer aware that these are not true Power Pentodes.


----------



## MajorNut1967

Wilder Amplification said:


> No...this is why I wish Major hadn't have said anything. Creates an un-needed scare.
> 
> Marshall amps have never applied negative bias to the suppressor grid pin on the amps they build for EL34s. They've always connected pin 1 to the cathode (pin 8) on their EL34 amps and as such the 6CA7s will work in any Marshall-made amp that's set up to run EL34s with a cathode referenced suppressor grid pin.
> 
> Some of us who build Marshall clones will negative reference the suppressor grid pin as Major did on his and the EH 6CA7s will not work in these amps without converting them to a cathode referenced suppressor grid pin. But not very many of us do this (Traynor is the only other amp maker I can think of that does this and I will soon be doing some experimenting of my own with it) so these amps are the exception to the rule.



Hey wankey boy, I explained it clearly about my amp and the Traynor in the beginning. And also Racko said his tubes died in two months! So if you want to go out on a Limb and recommend these to Marshall owners, you go right ahead but I see two reasons to use an alternative right here.

Oh update I just got an email from a mate of mine in New Zealand, he tried these in his 1971 Model 1987 50 watt. The tubes last a whole two hours before they super nova'd and took out his OT. He said that he had change the range res. in the bias circ. just to get it set correctly. He said they went poof and they are full of this white snowflake crap inside now. And that it is wired stock with pin 1 grounded as well as pin 8. So this wasn't a scare tatic but a word to the wise


----------



## thrawn86

Bummer deal Maj. So does everything check out now? (i.e. the OT)


----------



## MajorNut1967

thrawn86 said:


> Bummer deal Maj. So does everything check out now? (i.e. the OT)



Thanx Bro! all is well, nothing fried crispy chips. OT is fine the PT is what really got hot! but no major casualties yet, we'll see.


----------



## rjohns1

yeah, I tried these tubes a few years ago. lasted a whole month and pop.Luckily they didn't take anything with them.


----------



## MajorNut1967

rjohns1 said:


> yeah, I tried these tubes a few years ago. lasted a whole month and pop.Luckily they didn't take anything with them.



Thanks for the Info Mate. We are kind of seeing a bit of a pattern here.


----------



## racko7566

What really sucks is that they sounded better and felt better than any powertubes I've tryed so far. Be it I haven't tried any expensive tubes yet but ive tried eh el34s jj el34s and svetlana c's. 

My tubes didnt fry, but one thing ive learned here so far is to watch for and prevent (POOFS). My bias started drifting alot on one side, I switched them around and the drift moved over so I new it was a tube, Which I learned here. Thanks to you guys. So with my constant bias checking I feel confident enough to give them another shot. If this set goes then I'm done with them.


----------



## Wilder Amplification

As I've mentioned before, the screen grids in the power valves are really stressed in guitar amps. This is a known but hidden fact in the valve community as people would much rather blame the plates for not being able to handle the voltage. 

Some EL34s are only rated at 450V on the screens whereas others claim to be rated at 500 (Winged =C=). Well most of the newer Marshalls run them right at that limit or slightly higher. Some valves are more tolerant of this than others. It's becoming obvious that EH 6CA7s aren't very tolerant of the screen voltage in Marshalls.

The problem is that guitar amps have been running the same old style LC/RC supply in them for decades. The problem with this supply is that the plate voltage affects the screen voltage since they're on the same rail, although the choke/sag resistor and screen filter caps decouple the two, they're only a few volts apart from each other. This type of supply sets a limit as to how high you can run the plate voltage because of the fact that the screen voltage is only a few volts lower than the plate voltage. Once plate voltage is at 450-460V, ideally you can't go any higher than this because now you're at the screen voltage limit.


----------



## solarburn

I had one drift at the 3 month mark and got a replacement that I haven't used yet. I have other tubes in my DSL right now. I loved the tone of these too but I'm not liking what I'm hearing. I have a good set again but I have to really think about using them. One thing I do regularly is check bias. Like 3 times a week or when I am trouble shooting. If I use them I'm going to keep a very close eye on them. Meaning bias checks frequently.


----------



## solarburn

Wilder Amplification said:


> As I've mentioned before, the screen grids in the power valves are really stressed in guitar amps. This is a known but hidden fact in the valve community as people would much rather blame the plates for not being able to handle the voltage.
> 
> Some EL34s are only rated at 450V on the screens whereas others claim to be rated at 500 (Winged =C=). Well most of the newer Marshalls run them right at that limit or slightly higher. Some valves are more tolerant of this than others. It's becoming obvious that EH 6CA7s aren't very tolerant of the screen voltage in Marshalls.
> 
> The problem is that guitar amps have been running the same old style LC/RC supply in them for decades. The problem with this supply is that the plate voltage affects the screen voltage since they're on the same rail, although the choke/sag resistor and screen filter caps decouple the two, they're only a few volts apart from each other. This type of supply sets a limit as to how high you can run the plate voltage because of the fact that the screen voltage is only a few volts lower than the plate voltage. Once plate voltage is at 450-460V, ideally you can't go any higher than this because now you're at the screen voltage limit.



A tube site I was on recommended not using these on amps with PV's above 450V. The other site said they have a great record and are rated to handle 800V. I think we are starting to see whats what...


----------



## Wilder Amplification

solarburnDSL50 said:


> A tube site I was on recommended not using these on amps with PV's above 450V. The other site said they have a great record and are rated to handle 800V. I think we are starting to see whats what...



Yeah and it's not even the plates that's the problem. The problem is due to the ages old guitar amp power supply design that derives the screen voltage from the same positive rail in the supply that the plate does. As such, when you increase plate voltage, screen grid voltage also increases and it's always just a few volts lower than the plate. This is exactly why they recommend not to run them in amps with a plate supply of 450V or more...it's because the screen voltage ain't far behind it and the screens can't take it.

If you had them in an amp that had the screens on a different rail than the plate supply, you could run the plates close to 800 volts while running the screen supply at 400 volts and probably pull some big power out of them that way with the proper plate load. But ain't no way in hell they're gonna handle 800V when the screen supply running on the same rail would only be about 10 volts lower than that.


----------



## big dooley

so to say it in my words....
them tubes are more like a KT77, but with a misleading nametag?... 

a dutch webstore, selling these things, quotes them as "developed at exact philips design 6CA7" 

it's about time CP-tubes are named at what they are, with specs they actually have and not intend to have...


----------



## Wilder Amplification

big dooley said:


> so to say it in my words....
> them tubes are more like a KT77, but with a misleading nametag?...
> 
> a dutch webstore, selling these things, quotes them as "developed at exact philips design 6CA7"
> 
> it's about time CP-tubes are named at what they are, with specs they actually have and not intend to have...



I'd consider them to be more like a 6L6 that's made to run in an EL34 environment. The screen grid max rating of these things is MUCH lower than the screen rating on a KT77 (650 max for a KT77 as compared to a screen max rating of 400-450 for the EH 6CA7). I think they're hit/miss in the DSL/TSL amps because the DSL/TSL run a 460-470 volt plate supply, and due to the supply design topology (where the screens are powered from the same rail as everything else) the screens aren't far below the plate voltage. This runs the screens right at their max and taxes the screens a bit. Again some can tolerate it better than others.

I think this is what makes the Winged =C= EL34s a good match for Marshalls since they have a max screen voltage rating of 500 volts. Every other EL34 screen seems to be rated for 450ish.


----------



## big dooley

650V max screen rating for a NOS KT77? or does that include the CP-KT77's from JJ and gold lion? (if those are real KT77's of course  )


----------



## Wilder Amplification

big dooley said:


> 650V max screen rating for a NOS KT77? or does that include the CP-KT77's from JJ and gold lion? (if those are real KT77's of course  )



Not sure on the Gold Lion KT77s, but JJ KT77 screens seem to be rated a bit higher at 800 volts. At least that's what their datasheets claim. I'm a bit skeptical on that though.


----------



## big dooley

yes, i've been looking into those specs too... but if their KT77's seems a bit overrated, where would the EL34's and E34L's stand with their claimed 450V?


----------



## Wilder Amplification

big dooley said:


> yes, i've been looking into those specs too... but if their KT77's seems a bit overrated, where would the EL34's and E34L's stand with their claimed 450V?



450V on the 34 and 34L seems to be right on the money for these. I've ran these a bit higher than this (close to 500) and have never had them prematurely fail on me. But 450-500V seems to be the typical screen voltage spec range you'd see for any EL34. 450 is more common, but the Winged =C= EL34s seem to be rated at 500.


----------



## Joey Voltage

Wilder Amplification said:


> Not sure on the Gold Lion KT77s, but JJ KT77 screens seem to be rated a bit higher at 800 volts. At least that's what their datasheets claim. I'm a bit skeptical on that though.



Per our conversation earlier today, even the MO KT77's were not reccomended to have anywhere near 800V on the screens, I think even the old datasheets quote a maximum of 350Vdc for the screeens when used in a typical fixed bias class AB push pull amplifier. They make mention that when used in ultra linear designs, that a slightly higher screen supply can be tolerated IIRC. To my knowledge, the only valve curently being produce that can handle higher screen voltages in a run of the mill PA is the KT-88, and even they have limitations.

I blame some of the misuse on the manufacturers frankly. These days they don't seem to give a flying fuck, and don't go into detail of very important limiting elements, like the old datasheets used to. Not that I think anybody would pay attention anyway. the other part I blame on laxadasical design practices


----------



## solarburn

Looks like these tubes are in the same boat then with the Winged =C=s being a more reliable tube due to the higher rating. No wonder it has the rep it has. The rest are pretty equal though as far as the screen voltage goes. Kinda a crap shoot depending on the amp used...

I'll run mine longer and see. Really I'm not hearing any more horror stories then other tubes I've followed and even used. Enough to have me keep a close watch on them though since Racko's drifted around the 3 month mark too. I only had one drift and had it warrantied so I will give them so more time and see.

Winged =C='s are the only tube I find with a great rep especially from those who gig regularly.


----------



## Wilder Amplification

solarburnDSL50 said:


> Looks like these tubes are in the same boat then with the Winged =C=s being a more reliable tube due to the higher rating. No wonder it has the rep it has. The rest are pretty equal though as far as the screen voltage goes. Kinda a crap shoot depending on the amp used...
> 
> I'll run mine longer and see. Really I'm not hearing any more horror stories then other tubes I've followed and even used. Enough to have me keep a close watch on them though since Racko's drifted around the 3 month mark too. I only had one drift and had it warrantied so I will give them so more time and see.
> 
> Winged =C='s are the only tube I find with a great rep especially from those who gig regualarly.



The interesting thing is that the Winged =C='s are claimed to be the closest Mullard copy on the market, and yet even the original Mullard data sheets spec a design maximum screen rating of 425V, yet the Winged =C=s are supposedly rated a bit higher. The one thing I do have to say is that the Winged =C='s do seem to have the best track record in regards to reliability in Marshalls new and old so I think the proof is in the pudding there.

However, Joey does seem to bring up some interesting points regarding blaming the misuse on the manufacturers. Also, laxadasical design practices on the part of the amp builders comes into play...they're all using the same decades old single rail RC/LC power supply, which from one standpoint yes this does give the vintage sound that lots lust after. But the drawback is that your screen voltage rating sets the limit as to how hot you can go on plate voltage, and as such the amount of obtainable output power per pair of valves is limited by this design practice.

This is why it's been said countless times that 6550s in Marshalls aren't being utilized to their fullest potential in Marshalls. They're a high transconductance valve that's designed to pull big power per pair into a decent plate-plate load figure. However, they simply cannot do this on a single rail supply, or with the low plate loads found in Marshalls for that matter. Hence, this is also why I've stated many times that when you bias 6550s in a Marshall you go by the max figure for EL34s, not 6550s. Their transconductance was designed for higher plate loads than what's found in a Marshall for the plate loads they run at (data sheets spec a 5K plate-plate load on a 600V plate/300V screen supply for 6550s, yet Marshalls run a 3.4K in a 50 watter and a 1.7K in a 100 watter at whatever voltage they wanna run the valves at while referencing the screens at a point that's only a few volts lower than the plate). Too low of a plate load on a high transconductance valve (especially one that's too low for the valve it's designed to work with in the first place) can sent it into overcurrent quicker than shit.


----------



## MajorNut1967

big dooley said:


> so to say it in my words....
> them tubes are more like a KT77, but with a misleading nametag?...
> 
> a dutch webstore, selling these things, quotes them as "developed at exact philips design 6CA7"
> 
> it's about time CP-tubes are named at what they are, with specs they actually have and not intend to have...



Exactly Dooley,

They say they are like Philips version not even close! and we shouldn't have to be looking inside the tube make sure it what the fuck they say they are!


----------



## solarburn

Here's the Tube Store's review of actually using them:

At last something to replace the hole left since the EI 6CA7 went out of stock. These tubes sound every bit as good as the old EI tubes and are probably my favorite tubes for Hiwatt guitar amplifiers. It’s like they were made for each other. These tubes are like EL34’s on steroids. They handle high voltage and current without problems. As mentioned, there is nothing like a Hiwatt head powered by 6CA7 tubes and driving a 4x12 cab loaded with Fane speakers. This is classic rock tone at its finest. It’s the sound of Pete Townsend and The Who. The 6CA7 has more headroom than an EL34 and by the time you get it really crunchy sounding your pants are flapping in the breeze. Just the right amount of compression for great thick rock tone. Biasing levels can be dialed in from warm to hot without causing significant tonal changes. The EH is well constructed and should not pose any noise problems. If using these tubes in more reasonable systems the EH 6CA7 is capable of some really nice clean tones thanks to that extra headroom. If you want early Van Halen, these are not the tubes for you. If you want something loud and proud, you want to put the EH 6CA7 in your amp.

Here is their description of the tube:

Designed to the exacting specifications of the Philips 6CA7 tube, this classic tetrode returns to life in a big bottle design. The 6CA7-EH is built to withstand today's high-gain amps while still retaining the detailed tone and component integrity of the original. A direct replacement, with military reliability, for any EL34.

For me the tone delivers. I'm not comparing them to the NOS Philips at all. Reliability wise I don't know yet. Not looking good but I'll see. Description wise, a bit misleading to say the least...


----------



## solarburn

Here is the review of the KT-77 by the Tube Store so you can compare to the 6CA7:

The KT77 has been gone for many years and original NOS pieces are rare and expensive. JJ electronics has revived the design and released their own version. To my ears it sounds a lot like a 6L6 but has the heater current, max plate voltage and output rating of an EL34. The JJ KT77 has published specs that are identical to the original Genalex specs. The base has pin 1 included but there is no connection to any internal element. The sound is somewhere between an EL34 and a 6L6. Overall a nice balance of tone in bass, midrange and treble. The breakup is earlier than a 6L6 with more compression but not as compressed as the EL34. Unlike an EL34 this tube can be used in place of a 6L6 in Fender amps with minimal modifications. Vintage Fender amps usually use pins 1 and 6 as tie-off points for input grids and screen grids, mounting resistors on the socket. A standard EL34 can’t be plugged in because the input grid would be shorted to the suppressor grid via pin one. The KT77 avoids this. The only caveats are to ensure that your power transformer can supply an extra 500ma of heater current per tube and that the range of bias voltage adjustment is correct. If you have a Marshall amp and find EL34’s too compressed and 6550’s too crunchy the JJ KT77 may be just the ticket.


----------



## big dooley

> The only caveats are to ensure that your power transformer can supply an extra 500ma of heater current per tube and that the range of bias voltage adjustment is correct.


ok... this rises another question...
this is the story;
the JVM is supposed to be biased at 60Vdc on both points at 480Vdc on the plates (marshall recommendation) 
when i swapped those EL34's for KT77's in my JVM, when it came in i measured plate voltage... (never checked the plate voltage with the EL34's)
+/-435Vdc... nowhere near 480Vdc... bias was very cold at 45mV so turned it up, losing more voltage on pin 3... i've settled the bias at around 80mV @ 425Vdc 

the main voltage in our country is a bit lower then in the UK (220 vs 230/240) so obviously, this takes some toll as well, but after reading the above quote... do the KT77's play a role in this as well?

not that i care too much about it, the amp sounds rocksolid and the valves are working flawlessly so far (1,5 year of service, they had their burn-in in a biasdrifting DSL100)


----------



## Wilder Amplification

big dooley said:


> ok... this rises another question...
> this is the story;
> the JVM is supposed to be biased at 60Vdc on both points at 480Vdc on the plates (marshall recommendation)
> when i swapped those EL34's for KT77's in my JVM, when it came in i measured plate voltage... (never checked the plate voltage with the EL34's)
> +/-435Vdc... nowhere near 480Vdc... bias was very cold at 45mV so turned it up, losing more voltage on pin 3... i've settled the bias at around 80mV @ 425Vdc
> 
> the main voltage in our country is a bit lower then in the UK (220 vs 230/240) so obviously, this takes some toll as well, but after reading the above quote... do the KT77's play a role in this as well?
> 
> not that i care too much about it, the amp sounds rocksolid and the valves are working flawlessly so far (1,5 year of service, they had their burn-in in a biasdrifting DSL100)



When you bias valves, the more current they draw the more the plate voltage drops. This is because the valve in series with 1/2 the OT primary forms a voltage divider. As current draw through the OT primary increases, so does the voltage drop across it and as such the voltage drop across the valve does the opposite. Also the more current it draws the more of a load gets placed on the power supply. These power supplies are unregulated so this causes the supply voltage to drop some the more current you draw. The "stiffness" of the power supply controls how much it will drop.

Different valves drawing the same amount of current should end up roughly at the same plate voltage since the same load is being placed on the supply as well as that branch of the circuit.

However, I find it funny that Marshall can't even use PTs rated for their own mains voltage.


----------



## RickyLee

Wilder Amplification said:


> As I've mentioned before, the screen grids in the power valves are really stressed in guitar amps. This is a known but hidden fact in the valve community as people would much rather blame the plates for not being able to handle the voltage.
> 
> Some EL34s are only rated at 450V on the screens whereas others claim to be rated at 500 (Winged =C=). Well most of the newer Marshalls run them right at that limit or slightly higher. Some valves are more tolerant of this than others. It's becoming obvious that EH 6CA7s aren't very tolerant of the screen voltage in Marshalls.
> 
> The problem is that guitar amps have been running the same old style LC/RC supply in them for decades. The problem with this supply is that the plate voltage affects the screen voltage since they're on the same rail, although the choke/sag resistor and screen filter caps decouple the two, they're only a few volts apart from each other. This type of supply sets a limit as to how high you can run the plate voltage because of the fact that the screen voltage is only a few volts lower than the plate voltage. Once plate voltage is at 450-460V, ideally you can't go any higher than this because now you're at the screen voltage limit.



Sorry fellas for digging up such an old post, but this EH6CA7 issue might possibly be part of a problem I started hearing yesterday.

First off, I need to ask you Mr. Wilder, if you could tell me which models of the Traynor amps are biased with a fixed negative voltage on Grid 3?

The other question is what models of guitar amps have this dual rail B+ supply - have the screens on a different rail than the plate supply? 



As for my possible problem? I noticed yesterday that my '88 2205 that is running the EH6CA7's did not sound as good as it did this past weekend when I used it for two nights and quite a few hours each night. It went from sounding absolutely incredible to a bit harsh and lack of clarity, a bit distorted in the bass frequencies. In fact it was sounding so good (I did a few minor tweaks to it awhile back that made a huge impact for the better tonally), it made my Black Jubilee '89 2550 sound weak and boring. So now I am going to set it up here shortly and check it out and swap in a different brand of known good power tubes - maybe just put in a set of JJ E34L's. I know this 2205 runs at about 475V on it's B+.

I am starting to lean towards using my VariAC with my amps at all times as my service voltage at home is usually around 125VAC and the few times I have measured and checked service voltage at gigs, bars ect. I have seen some huge variances as well.

Anyway, I guess I better check out these EH6CA7's that are in my 2205 . . .


----------



## MajorNut1967

RickyLee said:


> Sorry fellas for digging up such an old post, but this EH6CA7 issue might possibly be part of a problem I started hearing yesterday.
> 
> First off, I need to ask you Mr. Wilder, if you could tell me which models of the Traynor amps are biased with a fixed negative voltage on Grid 3?
> 
> The other question is what models of guitar amps have this dual rail B+ supply - have the screens on a different rail than the plate supply?
> 
> 
> 
> As for my possible problem? I noticed yesterday that my '88 2205 that is running the EH6CA7's did not sound as good as it did this past weekend when I used it for two nights and quite a few hours each night. It went from sounding absolutely incredible to a bit harsh and lack of clarity, a bit distorted in the bass frequencies. In fact it was sounding so good (I did a few minor tweaks to it awhile back that made a huge impact for the better tonally), it made my Black Jubilee '89 2550 sound weak and boring. So now I am going to set it up here shortly and check it out and swap in a different brand of known good power tubes - maybe just put in a set of JJ E34L's. I know this 2205 runs at about 475V on it's B+.
> 
> I am starting to lean towards using my VariAC with my amps at all times as my service voltage at home is usually around 125VAC and the few times I have measured and checked service voltage at gigs, bars ect. I have seen some huge variances as well.
> 
> Anyway, I guess I better check out these EH6CA7's that are in my 2205 . . .



I'm not Mr. Wilder, but tell you what Traynor amps have it. Most of the YBA series that use EL34’s have the negative grid supply. Some Sunn amps and a few others I can't quite remember, some of the orange amps had to.

Have you noticed your power transformer or your output transformer getting warmer than usual?


----------



## Joey Voltage

RickyLee said:


> The other question is what models of guitar amps have this dual rail B+ supply - have the screens on a different rail than the plate supply?



Predominantly Bass amps. Take a look at some ampeg schemes andyou will them.


----------



## RickyLee

MajorNut1967 said:


> Have you noticed your power transformer or your output transformer getting warmer than usual?




I am going to set my 2205 up here in the living room and blast away for a bit. I did not notice my iron getting hotter than ususal as I basically just dug this amp back out a few weaks ago and took it out for a few gigs, being it was sounding so incredible after some work I had done on it. So you are saying that these EH6CA7's might be pullin' a bit more current than ususal? So I might see that my bias/idle current has drifted, or is it going to be under load/cranking I might see more draw? And the thing with the 2205, is that it uses the same power transformer as the 2204, but runs two extra preamp tubes more than the 2204. So I am thinking the 2205 power transformer should be quite warm under normal operating conditions to begin with? So that alone is something to be cautious about anyway regardless. 

Anyone know what the spec's are on these 2204/2205 50 watt Drake JCM800 era power transformers? Either they are quite close on filament spec's for the 2205's (7 total tubes) or have plenty to spare for the 2204's (5 total tubes)?


----------



## RickyLee

OK. I have no issues going on with my EH6CA7's in my 2205, though I am running over the rated limits of this tube. These tubes just spank the crap out of the JJ E34L's, and these tubes are not the issue that I am hearing with my amp. But I left the E34L's in there for the time being.

Also, the 2205 transformers are not that hot at all to the touch after using the amp for awhile. But then I was not even cranked close to what this amp is capable of putting out.


----------



## MajorNut1967

RickyLee said:


> I am going to set my 2205 up here in the living room and blast away for a bit. I did not notice my iron getting hotter than ususal as I basically just dug this amp back out a few weaks ago and took it out for a few gigs, being it was sounding so incredible after some work I had done on it. So you are saying that these EH6CA7's might be pullin' a bit more current than ususal? So I might see that my bias/idle current has drifted, or is it going to be under load/cranking I might see more draw? And the thing with the 2205, is that it uses the same power transformer as the 2204, but runs two extra preamp tubes more than the 2204. So I am thinking the 2205 power transformer should be quite warm under normal operating conditions to begin with? So that alone is something to be cautious about anyway regardless.
> 
> Anyone know what the spec's are on these 2204/2205 50 watt Drake JCM800 era power transformers? Either they are quite close on filament spec's for the 2205's (7 total tubes) or have plenty to spare for the 2204's (5 total tubes)?



The only reason I asked if your transformers were overheating is that that happened in my JCM 800 clone. And the reason it happened is because my JCM 800 clone as a native supply grid, which is not stock on a normal JCM 800. What was funny is that I had the tubes biased correctly well within spec and my power transformer got hot as hell. Normally all my transformers in my JCM 800 run exceptionally cool even after hour of loud plane can put your hand on top of the power transformer no problem.

The Drake Transformers for power should spec out as follows:

Input side should have taps for 120 V, 220 V, and 240 V

Secondary side should have 690 V with the center tap at 150 mA, the heater Tap should be 6.3 V at 5 amps.


----------



## kenm

Well I'm either the exception to the rule or just plain lucky but I've used the EH 6CA7's in a 1970 Traynor YBA-1 for years and have had no problems.


----------



## johnfv

Welcome to Marshall Forum Kenm. This actually is a rather old thread, if you search you can find details from a number of us using the EH 6CA7 with good results.


----------



## Alabama Thunderpussy

Your first post and it's to resurrect a 3 year old thread, and not only resurrecting a 3 year old thread, but doing it with anecdotal evidence.


----------



## johnfv

Alabama Thunderpussy said:


> Your first post and it's to resurrect a 3 year old thread, and not only resurrecting a 3 year old thread, but doing it with anecdotal evidence.



I say we give the new guy the benefit of the doubt. Let's not go all Wilder on his ass just yet...


----------



## pittbull

I just switched to the EH6CA7 after using EL34's and I wont go back to any EL34 brand thats for sure.The EH 6CA7 sound fantastic and the quality is very good,I hammer these tubes and they take the abuse.


----------



## tazzboy

Has anyone gotten a hold the new JJ 6CA7 to try out it mention on their web site that it is A.F. OUTPUT PENTODE?

JJ-Electronic - Vacuum tubes, Capacitors, Amplifiers - Power tubes


----------



## mickeydg5

Hello Kenm

No one should worry about substituting an EL34 with a 6CA7 or vice versa.
They both have an 8ET base which means that their pin connections are the same.

Philips/Sylvania 6CA7 (big bottle) and others modeled after its design like EH6CA7 and JJ6CA7 are Beam Pentodes or Beam Tetrodes. Most older data sheets call them Beam Tetrodes but later all refer to them as Beam Pentodes technically because they all have five electrodes. Their G3 (grid #3) are beam forming plates.

Also to add is that a KT77 is a beam type as well with a 7AC base which is the same base/pinout as the KT66 or 6L6 types.

The only difference between a 8ET and 7AC base is this:
8ET has pin#1 connecting to G3 and pin#8 connecting to cathode
7AC has no connection at pin#1 and pin#8 connects to both the cathode and G3

Other Pentodes have a suppressor grid for G3 instead of the beam focusing plates.


----------



## charveldan

I only use the best ^^^^^^


----------



## mickeydg5

If that were true then wouldn't your picture look more like this








Just kidding!


----------



## pittbull

6CA7's sound more open and bright then any EL34.They also sound more aggressive.EL34's have this compressed less open sound.


----------



## solarburn

I've found it depends on the circuit these tubes are in. Yeah they have an individual audio footprint no matter what amp they are in but can sound better or worse in different amps not to mention we don't all use the same speakers, pick ups, guitars etc...which all matter when stating a certain tube sound awesome. It may sound not so good in my set up cause of other variables.

I prefer the EH6CA7's in my JMP or my DSL50 over the Winged =C='s. I use to subscribe to them being the best CP EL34 out there. After rolling a few myself and not buying into Internet lore I found other power tubes pleased my ears more focused on what zone I play in and characteristics I prefer.

The EH 6CA7's are beastly and raw. I've never had a power tube make my amp meaner in a primal way like they do. It's weird but fun as hell. My other faves now are the GT34M's and JJ EL34L's. These are the 3 go too's for my amps and it was expensive to find out what turns me on.LOL


----------



## solarburn

pittbull said:


> 6CA7's sound more open and bright then any EL34.They also sound more aggressive.EL34's have this compressed less open sound.



Yes. I found the openness to equate to that raw beastly characteristic I hear when saturation is added. It's awesome. The top end isn't harsh either in my amps.


----------



## MartyStrat54

The best? Mullard xF1's or xF2's with dual getters. That's the best.

An RFT is better than a Winged C and costs about the same.


----------



## pittbull

The quality of Mullard tubes in the 70s were horrible.Alot of players including Eddie Van halen switched to 6CA7's because of that also they would go with 6550's.Marshall switched to 6550(amps coming to the USA)because of the quality of EL34's.


----------



## mickeydg5

Yes, there were problems with shipping EL34s in the 70s. I do not know why but there could have been a reason.

A big differences between a 6CA7 and an EL34 is that the 6CA7 is the American version which had/has a harder vacuum. This tends to give a different sound, same in character to that of the American 6L6 and a 6550.


----------



## MKB

Now IIRC the USA made 6CA7's back in the glory days were all beam tetrodes. About the only way you could get a true big power pentode was to get a Mullard EL34 or a 7591A. Also many tube substitution guides (anyone still have one of those??) listed the 6CA7 as a direct replacement to a EL34. So this tetrode/pentode issue has been around for quite a while. 

If you want to see tubes ran far outside their published specs, just check out almost any EL84 application. It appears you can run the plates fairly high as long as you keep the screens at 300V max. Mesa Engineering has been doing this successfully for years. BTW, if you use a largish RC on the screen grids, don't sell the amp as Randall has this patented and will come and git you. 

I always wondered why amp designers just didn't add a big zener to ground on the screens to keep the voltages under 300V. I once made a pair of homemade EL84 to EL34 adapters (like a THD Yellowjacket) and used zeners in the screen grid circuit to get the voltages down to 300V max, along with AC coupling on the signal grids to remove the amp bias and local cathode bias. I ran the plates of the EL84's at full amp voltage, around 495V IIRC. Those things worked perfectly in my 1987 clone, I never had a single problem with them.


----------



## Alabama Thunderpussy

Dan, can you PLEASE refrain from bandwagoning for longer than five minutes?


----------



## mickeydg5

Actually Tung-Sol 6CA7 tubes were power pentodes like the EL34s.


----------



## Tüßermensch

They are different tubes, what will make them somewhat similar (interchangeable) is their electrical happenings, which is the only of the concerns of the producers and of the engineers. the same thing happens in the transistor worlds to an extent.

You have to ask your self this one:

What is what is?

If it has a similar transconductance, a similar internal resistance, and A similar va to vg2 curves, hast that make it an el34 in terms to the sound? How close are those numbers to any real one you buy?

It's pretty much the picture abstract

-Heinrich


----------



## RickyLee

mickeydg5 said:


> Hello Kenm
> 
> No one should worry about substituting an EL34 with a 6CA7 or vice versa.
> They both have an 8ET base which means that their pin connections are the same.
> 
> Philips/Sylvania 6CA7 (big bottle) and others modeled after its design like EH6CA7 and JJ6CA7 are Beam Pentodes or Beam Tetrodes. Most older data sheets call them Beam Tetrodes but later all refer to them as Beam Pentodes technically because they all have five electrodes. Their G3 (grid #3) are beam forming plates.
> 
> Also to add is that a KT77 is a beam type as well with a 7AC base which is the same base/pinout as the KT66 or 6L6 types.
> 
> The only difference between a 8ET and 7AC base is this:
> 8ET has pin#1 connecting to G3 and pin#8 connecting to cathode
> 7AC has no connection at pin#1 and pin#8 connects to both the cathode and G3
> 
> Other Pentodes have a suppressor grid for G3 instead of the beam focusing plates.



Hey Mickey!

I just picked up a '73 Traynor YGL-3A head a few days ago. It has two TAD EL34B (Chinese made) and two old Sylvania 6CA7's in it. This Traynor has the negative bias voltage on pins 1, or the suppressor grid pin. I will not be trying the EH6CA7's in this amp after reading this thread of course.



I am wondering besides the basic EL34 types, what would be a good valve to try in this type circuit? And a very important question, what other valves do I need to avoid in this circuit? Is the JJ 6CA7 safe to run in it?


----------



## mickeydg5

I will have to check out the YGL-3A. Get back to you later.


----------



## thrawn86

Side note to the thread: It's coming up on almost the 1 year anniversary since we last heard from the Major. Hope we get to hear from him again someday.


----------



## RickyLee

I am just wondering if there's any issues with other EL34 valve brands like there was with the EH6CA7?


----------



## mickeydg5

I looked up the EH6CA7. It is claimed to be designed as a Philips type 6CA7. It is supposed to have an 8ET base. That is normal for an EL34/6CA7.

Unless it physically has different pin connections it should be ok to use. I do not have one to verify internal connections.

As far as use, it makes no difference if the suppressor is a grid type or beam type.

It should work in the Traynor YGL-3A. Traynor just employed a negative voltage to the suppressor fom the negative bias circuit.


----------



## mickeydg5

thrawn86 said:


> Side note to the thread: It's coming up on almost the 1 year anniversary since we last heard from the Major. Hope we get to hear from him again someday.


I believe he was on another board/forum and dissappeared from there as well.


----------



## thrawn86

Yep he did. Not just disappear, but pulled up stakes and such. Oh well, his way out there in the South Pacific.


----------



## RickyLee

mickeydg5 said:


> I will have to check out the YGL-3A. Get back to you later.



If you happen to look into this YGL-3A schematic, can you post the link to the copy you have? The copy I found is not all that good. That last schematic you looked at and gave me for the Custom Reverb was outstanding compared to my Traynor schematics.



Right now I am installing a Grounded power cord and I am going to remove the Ground switch and capacitor. But I am seeing something going from that circuit breaker (120VAC MAINS voltage) over to the Tremolo SPEED potentiometer. I have never seen anything like this in a Tremolo circuit.


----------



## mickeydg5

RickyLee said:


> If you happen to look into this YGL-3A schematic, can you post the link to the copy you have? The copy I found is not all that good. That last schematic you looked at and gave me for the Custom Reverb was outstanding compared to my Traynor schematics.
> 
> 
> 
> Right now I am installing a Grounded power cord and I am going to remove the Ground switch and capacitor. But I am seeing something going from that circuit breaker (120VAC MAINS voltage) over to the Tremolo SPEED potentiometer. I have never seen anything like this in a Tremolo circuit.


I do not think the actual tremolo photoresistor should be connected to the AC input. Did someone mess with the amplifier, mods?
It does show that Traynor used a neon lamp for power ON.
Try these:
http://www.el34world.com/charts/Schematics/files/traynor/traynor_markiii_ygl3_manual.pdf
http://www.el34world.com/charts/Schematics/files/traynor/traynor_mkiii_ygl3_3a.pdf


----------



## RickyLee

mickeydg5 said:


> I do not think the actual tremolo photoresistor should be connected to the AC input. Did someone mess with the amplifier, mods?
> It does show that Traynor used a neon lamp for power ON.
> Try these:
> http://www.el34world.com/charts/Schematics/files/traynor/traynor_markiii_ygl3_manual.pdf
> http://www.el34world.com/charts/Schematics/files/traynor/traynor_mkiii_ygl3_3a.pdf



Thanks again Mickey. I will start a thread later for this amp. This first schem I already have *"http://www.el34world.com/charts/Schematics/files/traynor/traynor_markiii_ygl3_manual.pdf"*

and this manual/schematic pdf page 10 (second to last page) matches the schematic that is stapled under the top lid of my amp. Except my schem does not have that handwriting on the bottom. 

And I also have a different copy of the alternate MK 3 version schematic in the second link you posted as well, which is page 2 of that schem. But your copy might be a bit more clear than mine.

Now the Fat and the Skinny. My amp is an aprox. August '73 model. I have early '73 date codes on some components. My MK 3 does not match either versions of those schematics completely. My Tremolo circuit is the type that runs off of the bias supply negative voltage or modulates the bias supply voltage. But everything in my amp looks stock or factory. I do not have a fan either. That looks like it was removed. And I have a "Mod" brand short reverb tank which I need to check to see if it is the correct impedance tank for this amp. My reverb is a bit weak.

And last night I noticed I do not have TH1 and TH2 that is tied to the output transformer primary plates. But there's two wires coming off the OT primary going to the board, so TH1 and TH2 were probably removed. I am not concerned about that.

The power cord was the Grounded three conductor type, but the Ground blade was broke off. So I installed a new Grounded end on the cord. The Ground switch and cap I did not remove yet. This switch was reversing polarity of the power cord last night before I added the Ground lug. Then after the amp was properly Grounded, that Ground switch did not switch polarity anymore. So that stumped me a bit, as I got too tired and went to bed. So I need to figure out why that is happening. I can't figure out exactly how the Ground switch works, because when I check continuity with all the numerous connections on it, everything is showing continuity due to the low resistance of the power transformer primary. As you already know, I would have to disconnect the PT to be able to trace it out correctly. I thought it might be cool to be able to switch polarity if needed, like running into backwards wall outlets at gigs. But I am thinking I just need to remove that Ground switch altogether.

And my amp has that same burn mark on the turret board around the 470 Ohm 10W B+ resistor after the AC to DC rectifier and that 470K 10W screen resistor. All resistors look good and measure correctly. But I want to ask you if I should change that single shared 470R 10W screen resistor out to individual 1K 5W screen resistors? 

And it does have all the original e'lytic caps, so I need to replace those as well. And that odd 100R 10W resistor I thought was tied from the 120VAC Mains to the Tremolo circuit is not the case. That 100 OHM 10W resistor must have went to the fan. And my power amp circuit matches close to the pdf page 10 manual/schem, as I have the 1K NFB loop resistor. Man, that is quite a bit of NFB LOL! I would think installing a Resonance control as well as a Presence control would do good things for this amp.

Tonally, this amp is actually pretty sweet. Very similar to a Fender Twin but with a weaker reverb circuit. And this amp gets very LOUD!

EDIT: I forgot to mention that my "Extension Speaker" jack was wired wrong. If you plugged a second speaker cab into it, it would send Positive to Ground for both speaker jacks. The jack looked original, but it was just a tip ring sleeve old switchcraft, but not the open or closing type like on the first speaker out jack. Except the wire coming off the first "Speaker Out" positive terminated on this Ext. jack ring terminal. Then there was a jumper wire going from that ring to the positive terminal LOL. Ground connection is made by the jacks being mounted to the chassis.


----------



## mickeydg5

Ricky
Start a new thread.
All of the Traynor YGL-3 designs have tremolo that tie to the negative bias circuit.


----------



## chuckelator

Ok, so I just noticed this thread...and spare me the super technical info (as most of it goes right over my head) But, those GE 6CA7's I have in my 1987 aren't the same as the current production 6CA7's?

Good to know!!! I guess I'll have to seek out some NOS ones when the ones I have in the old beast finally go! Luckily, my tech told me they still test extremely strong, and are still very well matched!


----------



## mickeydg5

chuckelator said:


> Ok, so I just noticed this thread...and spare me the super technical info (as most of it goes right over my head) But, those GE 6CA7's I have in my 1987 aren't the same as the current production 6CA7's?
> 
> Good to know!!! I guess I'll have to seek out some NOS ones when the ones I have in the old beast finally go! Luckily, my tech told me they still test extremely strong, and are still very well matched!


Chuck, you should be able to use any 6CA7 in your EL34 type 1987 model amplifier.


----------



## chuckelator

mickeydg5 said:


> Chuck, you should be able to use any 6CA7 in your 1987 model amplifier.



My thing though...will it sound even close to the same??? I know I love the tone of how my amp is now, but if I put a pair of these new 6CA7's in, will it be similar???


----------



## RickyLee

chuckelator said:


> Ok, so I just noticed this thread...and spare me the super technical info (as most of it goes right over my head) But, those GE 6CA7's I have in my 1987 aren't the same as the current production 6CA7's?
> 
> Good to know!!! I guess I'll have to seek out some NOS ones when the ones I have in the old beast finally go! Luckily, my tech told me they still test extremely strong, and are still very well matched!



If you do not crank the amp to extremes, those GE's should last quite a long time. I am thinking the ones that came in my amp might be original or OEM. And they seem quite strong as well.


----------



## chuckelator

RickyLee said:


> If you do not crank the amp to extremes, those GE's should last quite a long time. I am thinking the ones that came in my amp might be original or OEM. And they seem quite strong as well.



Surprisingly enough, that amp wasn't set up for 6CA7's when I got it (my uncle gave me the amp) and as such, when I took it to my tech for a check-up (wanted to make sure it was in top shape before I recorded with it) those tubes were running twice as hot as they should have been, and have been doing so for more years than I even know (not sure when my uncle dropped those tubes in, so it's been a long time, as he rarely used the amp anymore)

a piggy-back resistor fixed that, but like I said, when my tech tested the tubes, he told me they're in surprisingly good shape, especially considering the beating they've taken over the past 30-40 years (and especially the past 3 or 4 years that I've been using it consistently)


----------



## mickeydg5

Chuck
All tubes will have a general sound characteristic which are tied to style and manufacturer process.
Old or vintage 6CA7 will sound different than current production. American tubes had specific manufacture technique and had harder vacuum. You will not find those exact same qualities in todays 6CA7 tubes, but manufacturers are trying to replicate them. Lots of people do find favorable qualities in current production tubes. A current production 6CA7 should sound more like a vintage one than does any EL34 though, I would think.
If you want authentic 6CA7 though, vintage Sylvania or GE is it.


----------



## chuckelator

mickeydg5 said:


> Chuck
> All tubes will have a general sound characteristic which are tied to style and manufacturer process.
> Old or vintage 6CA7 will sound different than current production. American tubes had specific manufacture technique and had harder vacuum. You will not find those exact same qualities in todays 6CA7 tubes, but manufacturers are trying to replicate them. Lots of people do find favorable qualities in current production tubes. A current production 6CA7 should sound more like a vintage one than does any EL34 though, I would think.
> If you want authentic 6CA7 though, vintage Sylvania or GE is it.



Looks like I'll be seeking out some GE 6CA7's as back-ups then in the near future, as I don't wanna change any of the magic that goes on inside my amp.

Thanks Mickey!


----------



## okbassplayerguy

OK, so I just ordered a matched pair of EH6CA7 tubes to try in my JTM60 amp, and then I find this thread about the dangers of using them. So should I send them back for something else, or give them a try, cautiously??

I installed a muffin fan on the tube guard below the power tubes and it pulls a good draw and seems to be keeping things cool. Would this be of any benefit if trying to run this tube?


----------



## MartyStrat54

There's no problem running the 6CA7's in your amp. The 6CA7's do not put off anymore heat than an EL34.


----------



## okbassplayerguy

Thanks Marty, they should be in the middle of next week. I'll let you know how it goes.


----------



## MartyStrat54

I'm running four of them in my TSL122 and I also had them in a TSL100. I really like them.

Are you going to bias the amp yourself? 

I run about 67 percent in the TSL.


----------



## okbassplayerguy

Not without some help. A friend of mine does his own amps, so I will probably get him to help me. I have the schematic so hopefully we can get it set properly.


----------



## okbassplayerguy

I had read about the screen voltage being an issue, and also when trying to run these in Marshalls that had had some kind of mod done on thiem. Do you have anything you could add that would be of help? Thanks, Ed


----------



## MartyStrat54

Certain older non Marshall amps had a slightly different pin configuration. In your amp it is a moot point. If there was a problem, then the tube stores would specify what amps would not work with 6CA7's. They are not going to sell a tube that could damage someone's amp.

I don't know what you mean about screen voltage? The screen voltage is a little lower than the plate voltage. I don't recall your amp having any wild high voltage.

Also if I recall, your amp is a little bit of a bitch to adjust the bias. I think the bias pot is located on one end of the chassis on the PCB. Make sure you guys are careful when making the adjustment.

Here is an old link.

http://www.marshallforum.com/workbench/16651-6ca7-vs-el34.html


----------



## okbassplayerguy

Thanks again for the input. The reference about screen voltage was pertaining to the voltages that Marshall's output damaging the tubes because the screens can't take that high a voltage (I think)???


----------



## okbassplayerguy

Marty, I got my EH 6CA7's in today and am anxious to try them in my JTM60. The tubes have some specs on each box (34/4.7 & 34/4.8). Can you confirm for me what each means? Thanks.


----------



## big dooley

okbassplayerguy said:


> Marty, I got my EH 6CA7's in today and am anxious to try them in my JTM60. The tubes have some specs on each box (34/4.7 & 34/4.8). Can you confirm for me what each means? Thanks.



i'd say those are the figures for either cathode/plate current (34mA) and screen current (4.8mA & 4.7mA) at a given bias voltage and plate voltage...
if so, this pair is bloody well matched


----------



## MartyStrat54

Dooley nailed it.


----------



## okbassplayerguy

Thanks guys, I got these from Amplified Parts in Tempe, Arizona. My experience ordering from them has been really positive.


----------



## okbassplayerguy

Probably a stupid question, but can I use this information to help in setting the bias on my amp?


----------



## MartyStrat54

That info came from the sellers test equipment. You need to get your plate voltage and then figure out your bias setting.

If your plate voltage is 470, then you take 70 percent of 25 watts which is 17.5 and you divide 470 into 17.5. This gives you .037, or 37mA. Of course, 70 percent is generally your max amount. I usually bias at around 65 percent. 34.5 would be 65 percent. (Which BTW is what is written on your box.)


----------



## okbassplayerguy

Thanks Marty, I appreciate your assistance.


----------



## proxy

Once i put in my amp 6CA7 I never looked back
Even better.
I got myself vintage EI 6CA7 tubes really good stuff.
I remember when I first tried EH 6CA7 how pleasantly I was surprised.
For good.
I continued to try different 6CA7 tubes then one day I got EI 6CA7's...
It was phenomenal experience.
EI sounded so much more organic....tough and rough....fabulous for Marshall .........


----------



## danfrank

big dooley said:


> so to say it in my words....
> them tubes are more like a KT77, but with a misleading nametag?...
> 
> a dutch webstore, selling these things, quotes them as "developed at exact philips design 6CA7"
> 
> it's about time CP-tubes are named at what they are, with specs they actually have and not intend to have...



Philips designed the EL34, not the 6CA7, which is an American designed tube. The Dutch web store's information is incorrect.

6CA7 is an American beam tube design
EL34 is a European power pentode design
It has always been this way…

American and European tube manufacturers have always tried to make "equivalent" charts to their tubes and tubes from the other side of the Atlantic.
Some times they are very similar; in the case of the EL34 and 6CA7, they are not. These 2 types have similar transconductance and plate resistance values, nothing more. They don't even bias the same.

The safe way is to tie pin 1 of the socket to pin 8. Problem solved.


----------



## danfrank

mickeydg5 said:


> I looked up the EH6CA7. It is claimed to be designed as a Philips type 6CA7. It is supposed to have an 8ET base. That is normal for an EL34/6CA7.
> 
> Unless it physically has different pin connections it should be ok to use. I do not have one to verify internal connections.
> 
> As far as use, it makes no difference if the suppressor is a grid type or beam type.
> 
> It should work in the Traynor YGL-3A. Traynor just employed a negative voltage to the suppressor fom the negative bias circuit.



Actually, it does make a difference… The OP said that his transformer became super hot and the amp sounded bad; 2 great indicators that the amp was oscillating like crazy with the 6CA7 tubes.
Beam tubes aren't meant to be operated with the beam plates at a different potential than the cathode; that's why the beam plates are always internally tied to the cathode in beam tubes.
EH's 6CA7 base pinout is bad design by EH; being a beam tube, the beam plated should have been connected to the cathode internally. Bad oversight on their part.


----------



## mickeydg5

The original poster had a problem with his amplifier and the EH6CA7 of that time.
He also stated others having problems with those tubes at that time with various amplifiers.

I gathered the problem was a manufacturing defect or problem by EH and is not related to the original design of either 6CA7 or EL34.

His heat problem may have been most likely due to bad tubes and even other implemented components, not (the original) tube design itself.

Not all beam pentodes have their G3 tied to the cathode as is the case of a true 6CA7, Sylvania (acquired by Philips).
It is not Electro-Harmonix's tube base pinout. It is not bad. It is the original pin layout of 8ET for all 6CA7 and EL34 power tubes.

And yes they can operate with G3 at a more negative reference level as compared to cathode, whether fixed or self biased.


----------



## alerich

Wilder Amplification said:


> If you had them in an amp that had the screens on a different rail than the plate supply, you could run the plates close to 800 volts while running the screen supply at 400 volts and probably pull some big power out of them that way with the proper plate load.



+1

I have a Sovtek Mig60 that has a stacked power supply. The mid point between the two halves of the supply is for the screen grids. it runs about 350VDC. The B+ for the plates is derived at the top and runs about 640VDC. I run Tung Sol EL34B tubes in it. Happy as a clam at the higher plate voltage.

https://irationaudio.files.wordpress.com/2015/03/sovtek-mig-60-schematic.jpg


----------



## RickyLee

alerich said:


> +1
> 
> I have a Sovtek Mig60 that has a stacked power supply. The mid point between the two halves of the supply is for the screen grids. it runs about 350VDC. The B+ for the plates is derived at the top and runs about 640VDC. I run Tung Sol EL34B tubes in it. Happy as a clam at the higher plate voltage.
> 
> https://irationaudio.files.wordpress.com/2015/03/sovtek-mig-60-schematic.jpg



I was just gazing into that schematic for awhile.



So I am seeing that this split power supply has the screens powered off the mid point of the first filter stage series filter caps. Can this same method be performed on a 100W Marshall style totem pole first filter stage, where it has the resistor across each filter cap?

I have a few old amps that run well over 540V on the screens and would like to get the screen supply much lower.


----------



## mickeydg5

Most anything is possible.


----------



## RickyLee

mickeydg5 said:


> Most anything is possible.



I was just finishing up a few minor adjustments on that old Mitchell Pro 100. I put new filter caps in it and added a .1uF 600V cap on the cold side of the standby switch. The filtering/power supply is now close to a Mesa Mark II.

I was trying a set of Russian GT KT66's in it after adding a bias adjust pot. The amp is running 510V on the plates and screens, the KT66's are a 10 rated set and running a great deal hotter than the similar set of 10 rated KT66's I puty in my Plexi build. I had -67V on the control grids and one of the KT66's was running 10mA hotter than its mate. I noticed a small orange glow on the plate of that hot running valve. The bias idle was steady, but 10mA hotter than the other. 

So that has me asking you if that means that KT66 with the plate glow is done/bad? I pulled them from the amp already but just curious if there is any hope or life left in that KT66? 510V is obviously too hot for these KT66's.

I pulled out the VariAC and lowered the plate/screen voltage down to 460V and that plate glow was still there though not as big of an area. Did not try lowering the VariAC any lower as the heaters on this amp were down under 5.6VAC.

Bummer as this power transformer runs a bit low on the heaters, where I normally see 7VAC heater strings with my 125V plus wall voltage. This amp was at 6.1VAC with 125V wall voltage. And that was with only two of the four power valves running.


----------



## RickyLee

Trying to learn and read up on this subject. Seems I can not tap the screen supply from the center of two series connected filter caps. At least for my configuration which has a center tapped HT.

I am still trying to figure out if you can tap for the screen grid supply from the center of a totem pole node if you have the full wave bridge rectifier with no center tap. 

The obvious solution to lower my screen supply would be a dual rail supply using two power transformers, adding in a small additional power transformer and rectifier circuit for the screens. Or for the screens on down to the preamp, and using the original high voltage PT secondary only for the first first stage valve plates.



ADD: Did find this layout: 

https://docs.google.com/viewer?url=...m/techinfo_old/old_amps/2165-rd_&_2100-rd.pdf

I will start a thread on this subject.


----------



## What?

solarburnDSL50 said:


> Yes. I found the openness to equate to that raw beastly characteristic I hear when saturation is added. It's awesome. The top end isn't harsh either in my amps.



Bumping this thread. I'm looking at the Tung Sol EL34B for a retube of my DSL-50, but after running into some info on the 6CA7, I'm considering that as well. I see that EH and JJ have these available. What has been your experience with durability of the EH 6CA7's? Or anyone else for that matter, on durability/reliability of EH or JJ 6CA7's.

Unless I have got my wires crossed, 6CA7's can be ran in DSL's without any circuit changes?

Whichever tubes, I'm looking for tighter bass, lower compression, more warmth in my DSL-50 with a 212 cab. But above all else, no mechanical noise. Rattle drives me crazy.


----------



## Kinkless Tetrode

What? said:


> Bumping this thread. I'm looking at the Tung Sol EL34B for a retube of my DSL-50, but after running into some info on the 6CA7, I'm considering that as well. I see that EH and JJ have these available. What has been your experience with durability of the EH 6CA7's? Or anyone else for that matter, on durability/reliability of EH or JJ 6CA7's.
> 
> Unless I have got my wires crossed, 6CA7's can be ran in DSL's without any circuit changes?
> 
> Whichever tubes, I'm looking for tighter bass, lower compression, more warmth in my DSL-50 with a 212 cab. But above all else, no mechanical noise. Rattle drives me crazy.



I have used the EH for many years. I have never had a problem with the EH6CA7. The only failure was when I dropped one on a hard floor. 

The should go right in place of the EL34. They will, most likely, require more negative voltage at pin 5 than most EL34s, but as long as the bias pot has enough range they should require no circuit changes.


----------



## solarburn

What? said:


> Bumping this thread. I'm looking at the Tung Sol EL34B for a retube of my DSL-50, but after running into some info on the 6CA7, I'm considering that as well. I see that EH and JJ have these available. What has been your experience with durability of the EH 6CA7's? Or anyone else for that matter, on durability/reliability of EH or JJ 6CA7's.
> 
> Unless I have got my wires crossed, 6CA7's can be ran in DSL's without any circuit changes?
> 
> Whichever tubes, I'm looking for tighter bass, lower compression, more warmth in my DSL-50 with a 212 cab. But above all else, no mechanical noise. Rattle drives me crazy.



I find the EH version demonstrated more note separation or articulation especially while soloing. I haven't tried the JJ 's yet however I have a pair coming soon. They are going in my Bugera head with a pair of EH 6CA7's already in it.

I prefer the 6CA7's because their articulation and feel. Sometimes you have to try tubes out. I will listen to reviews of them bottom line is my ears and what I like decides what goes in. Don't want to push my ears and taste on anyone. I've earned what tickles my fancy by trial and error as well as spending a few fists full of dollars. 

I've had one pop on me and one drift beyond bias range. That's 2 that fell short. I've had a pair last a few years now. Like any tube manufacturer/type bad ones happen.

If you get some let us know. I really dig the EH version. Going to get a fresh quad when I can.


----------



## What?

solarburnDSL50 said:


> I find the EH version demonstrated more note separation or articulation especially while soloing. I haven't tried the JJ 's yet however I have a pair coming soon. They are going in my Bugera head with a pair of EH 6CA7's already in it.
> 
> I prefer the 6CA7's because their articulation and feel. Sometimes you have to try tubes out. I will listen to reviews of them bottom line is my ears and what I like decides what goes in. Don't want to push my ears and taste on anyone. I've earned what tickles my fancy by trial and error as well as spending a few fists full of dollars.
> 
> I've had one pop on me and one drift beyond bias range. That's 2 that fell short. I've had a pair last a few years now. Like any tube manufacturer/type bad ones happen.
> 
> If you get some let us know. I really dig the EH version. Going to get a fresh quad when I can.



I agree about trying things out for yourself, and I have noticed in your posts the lack of pushing your opinion. Much appreciated.


----------



## ampmadscientist

MajorNut1967 said:


> If you are contemplating using the Electro Harmonix 6CA7 in your older/vintage Marshall, Traynor or with an amp with a negative grid supply; I would stay away from this! The Electro Harmonix 6CA7 is not and I repeat “NOT” a Power Pentode like the original 6CA7’s were, in fact they are Beam Tetrode as stated on the Electro Harmonix website. But the issue is tube venders are saying it is a direct substitute for an EL34 in all situations. Be careful, its not! I you really want to use these tubes in your amps make sure you don’t have a negative grid supply mod or a Traynor Amp. In fact even if your older/vintage Marshall amp has (pin1) & (pin 8) tied to ground, I would stay away from these tubes.
> 
> I found this out on my own. My JCM 800 build project was the test bed, I had told Marty I got a set of Electro Harmonix 6CA7’s to try in it later after the amp broke-in, well I put them in today. I couldn’t get them to bias correctly. So I bumped up he bias voltage up and got them in range, but they amp sounded like crap an the PT was hot as hell. Then friggin Wilder clued me in, after all the bullshit I went through, that it’s not a real power-pentode but a damn Beam Tetrode wannabee. Wilder found it out on Solar’s amps, but didn’t bother to tell me! LOL



The problem being that pin 1 of the socket is hooked to bias negative voltage, instead of grounded.
This is used on some Traynor and Peavey Windsor (or other) EL34 amp designs.
The negative voltage makes the tube less sensitive --------compared to grounding pin 1, as it is in Marshall amps.

Any 6CA7 will have this problem not just Electro Harmonix...You need to use EL34 instead for your Traynor.

I have used 6CA7 a lot, but the circuit has to be the correct one for this tube.
Biasing 6CA7:
You need to change 1 resistor in the circuit to set the correct bias range for this tube. There is nothing wrong with the tube itself, and you can use it in Marshall amps no problem (if you know how).

So you see? It's not the tube that's at fault here. It's lack of knowledge "about" the tubes and about the amps.
There is nothing wrong with EH 6CA7.


----------



## solarburn

I've been running the 6CA7'S in Both my Bugera Infinium model amps which self biases same pinned tubes. Plus the amps shut down when a power tube shorts. I've replaced fuses a couple of times due to bad power tubes. No other damage down the line which can happen when tubes pop.

It's nice being able to try power tubes out in a self biasing system and the circuits are based on a vintage Marshall SL/900. I play in the power section(loud)most of the time and challenge them light bulbs consistently. They're(tubes)not all sturdy for sure. Many guitarist don't get to go loud consistently due to where they live or venues keeping stage volume down going through house systems.

I test those lil fuckerz out cause I love the sound/feel of being in a certain amps power band. I'm surprised I don't go through more speakers too.

I added JJ 6CA7'S to my 1960I and got meaty open old school tone/dynamics dripping harmonic feedback when I ride guitar volume. Fresh tubes are fun. I love when a tube change puts a big ole smile on my face.


----------

