Dc Heater Filaments And Running Relay Coils Updated: Hot Rodded Studio 15

RickyLee

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Nice clip David. Yeah, I am considering drilling a few more holes, one for an additional gain pot and then holes on back for a loop. I have already drilled two 12AX7 socket holes so it is no big deal really. I want a very small portable amp that is useful for my needs.

As for this thread, it is an old threads that I added on to. Two different situations really. I probably should had just made a new thread.

I already have the supply voltage in place for the relay so that is why I went the route of just adding in the relay itself instead of using up one of my Granger boards. All I need to do is swap C21 for a 1500uF and my situation is solved. Just not sure if I should keep the stock tone stack in this amp as I am not liking that part of the circuit at this point.

I was thinking the Studio 15 tone stack has some branch similarities to the Jubilee. But it is not reacting the same to my ears. Obviously the bass control is the big difference for sure.
 
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RickyLee

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Just got done looking comparing the Jubilee and Studio 15 tone stacks. It then hit me upside my head why I am not digging the tone of my modified 2nd channel I am installing in my Studio 15. Basically, I need to install a pre phase inverter master volume right after the tone stack, or install a grid load there to attenuate the signal. I was having some oscillaions and an overall over loaded signal sound with my two added gain stages. So basically, it would be somewhat similar to playing a 2204 or Jubilee with the master volume on permanent 10. The Studio 15 master volume is a post phase inverter master volume.

So maybe there is hope for implementing a high gain 2nd channel into the Studio 15 format. I might also try swapping out the JJ 6L6GC for some old KT66HP.

If you are reading this @mickeydg5 , that is what I wanted to clarify as I know you are a Jubilee guy. The Studio 15 tone stack could be converted to a Jubilee tone stack but I am now thinking I might be fine with it as is. I am trying to leave it stock as much as possible so the 1st channel will be stock Studio 15. That is where I am going with this project basically.

Also just noticed that the Studio 15 V1B grid load reference is the front of the tone stack at the gain pot. I am going to add a master volume between the treble pot and V1B.
 
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mickeydg5

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This is a modified Studio 15 being referenced. Did you replace transformers and if so with what?

If the PT was not replaced/upgraded then do not load KT66. If you have 6L6 loaded especially with an extra preamp tube then the filament rating is beyond maxed already.

I am going to guess that the stock OT may be stressed as well.

Why not use the 6V6? Those are great power tubes.
 

mickeydg5

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The whole key to 'high gain" or what I call more overdrive/distortion is the build up and then break down of the signal. The signal has to be broken down or divided into a smaller version of itself in order to be controlled and reused. So yes some sort of loading system or volume control is required with each added gain stage.

It has to be set up correctly to take advantage of both channels when switching.

I am assuming the second channel is the implementation of cascaded gain stages switched in and out of the original circuit. Is that correct? Where are you placing the added gain stages?

The TMB EQ controls can be handled any sort of way. Jubilee more difficult, regular TMB less difficult but if you can make the stock circuit work as is or with tweaking then why not leave it?
 

NewReligion

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Nice clip David. Yeah, I am considering drilling a few more holes, one for an additional gain pot and then holes on back for a loop. I have already drilled two 12AX7 socket holes so it is no big deal really. I want a very small portable amp that is useful for my needs.

As for this thread, it is an old threads that I added on to. Two different situations really. I probably should had just made a new thread.

I already have the supply voltage in place for the relay so that is why I went the route of just adding in the relay itself instead of using up one of my Granger boards. All I need to do is swap C21 for a 1500uF and my situation is solved. Just not sure if I should keep the stock tone stack in this amp as I am not liking that part of the circuit at this point.

I was thinking the Studio 15 tone stack has some branch similarities to the Jubilee. But it is not reacting the same to my ears. Obviously the bass control is the big difference for sure.

I don’t know about the Studio 15 but the Jubilee 2555 TS is anode driven.
 

RickyLee

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This is a modified Studio 15 being referenced. Did you replace transformers and if so with what?

If the PT was not replaced/upgraded then do not load KT66. If you have 6L6 loaded especially with an extra preamp tube then the filament rating is beyond maxed already.

I am going to guess that the stock OT may be stressed as well.

Why not use the 6V6? Those are great power tubes.

Try this from my phone while I'm in Norms restaurant lol.

Power xfmr is a multi secondary Weber. 5A 6.3 tap. Output xfmr is a 3203 Artist. I went with 6L6 for the secondary impedance primarily but might go back to 6V6 later too. Artist 30W runs two EL34. Salmon is coming. Time to eat. Will come back when I'm home . . . .
 
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RickyLee

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The whole key to 'high gain" or what I call more overdrive/distortion is the build up and then break down of the signal. The signal has to be broken down or divided into a smaller version of itself in order to be controlled and reused. So yes some sort of loading system or volume control is required with each added gain stage.

It has to be set up correctly to take advantage of both channels when switching.

I am assuming the second channel is the implementation of cascaded gain stages switched in and out of the original circuit. Is that correct? Where are you placing the added gain stages?

The TMB EQ controls can be handled any sort of way. Jubilee more difficult, regular TMB less difficult but if you can make the stock circuit work as is or with tweaking then why not leave it?

I don’t know about the Studio 15 but the Jubilee 2555 TS is anode driven.

At this point, I have two 12AX7 sockets added to the amp. But I am only using one at this time. That extra 12AX7 gives me two cascaded stages switched in after the gain pot and before the tone stack. Just a simple interstage of a paralleled 470pF/470K going into 1st extra stage and 33nF coupler. Then 2nd stage is 33nF coupler into a 330K/330K divider. 100K plates on both and still tinkering on the cathodes but 10K on both with .68uF cathode bypass on 1st and .1uF cathode bypass on 2nd. This all gets switched out and amp goes back to stock preamp. Going to restructure B+ rail later.

Studio 15 tone stack looks to have its roots or actually be the roots of the Jubilee tone stack as the Studio 15 did come out in 1985.

Going in right now to add in a master volume . . . .
 

mickeydg5

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At this point, I have two 12AX7 sockets added to the amp. But I am only using one at this time. That extra 12AX7 gives me two cascaded stages switched in after the gain pot and before the tone stack. Just a simple interstage of a paralleled 470pF/470K going into 1st extra stage and 33nF coupler. Then 2nd stage is 33nF coupler into a 330K/330K divider. 100K plates on both and still tinkering on the cathodes but 10K on both with .68uF cathode bypass on 1st and .1uF cathode bypass on 2nd. This all gets switched out and amp goes back to stock preamp. Going to restructure B+ rail later.

Studio 15 tone stack looks to have its roots or actually be the roots of the Jubilee tone stack as the Studio 15 did come out in 1985.

Going in right now to add in a master volume . . . .
The Volume control before the PI will help the situation.

The oscillation is probably from lack of stage speration via B+ rail nodes. Get some 4.7k resistors and a another 33uf or 22uF supply capacitor in there.
 
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RickyLee

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The Volume control before the PI will help the situation.

The osciallation is probably from lack of stage speration via B+ rail nodes. Get some 4.7k resistors and a another 33uf or 22uF supply capacitor in there.

Yeah, needs at least one more node. That will be later after I get the voicing in the ballpark.

I tried attenuating some signal after the 2nd stage with a Jubilee Lead channel clipper circuit. It helps a bit and then gives it some added bite. But at this point, it still sounds too bright and ratty lol. I am going to remove the .68uF and .1uF cathode bypass caps another day. Also should try some 6V6 as it is just too loud - as in can't play it at a lowish volume. Having a hard time here at home cranking amps for testing. The added master volume helped but not much - used a 500K pot.

I then started wondering about the 1X12 speaker. So just plugged my JVM 410H head into this combos 1X12 and the JVM sounds great at very low volumes. I am way off base here for sure. My hat goes off to my JVM 410H once again as it is a great amp for sure.

So I am now also wondering if my layout is worth still kicking. I should just go more towards a Jubilee layout as it is already in that ballpark. Or try removing one of those added stages and go with that for awhile.

Or the big one - rewire it to fall more in line with a 15W Plexi by moving the tonestack and trying a cathode follower. Even a plate follower could be cool Plexi style. I will first try removing the two cathode bypass caps first another day. And maybe lower plate resistor values in the phase inverter too.
 
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mickeydg5

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The 500k MV helped but not much with what? It aint going to get ride of oscillations. Your monster is feeding all the way to the PI stage right now. That is why stage and node layout is important.

You have a great little amplifier right there. You have already bumped up the output to double it seems. Work with it and make it a mean modified 4001 Studio 30.

Leave the PI plate resistors. They are ok for now.
 
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RickyLee

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The added master volume after the treble pot helped attenuate some signal and allow that original circuit master volume, which is a post phase inverter MV, to be turned up a bit higher. But then not much higher really. That PPIMV has to be close to max for the signal/sound to have better clarity and not sound so harsh and ratty.

I should have added I have a switch on back that goes between stock cathode bias and fixed (adjustable) bias. The switch basically adds in a 1 ohm bias resistor across the original 270R/22uF cathode bias. It does make a slight difference in volume between these two settings. I am running it fixed bias right now at aprox. 50% dissipation of 30W (6L6).

And then I have a switch that gives me a lower B+ option from this multi-voltage Weber WPTGP power xfmr. I have it on the higher voltage setting now which is 369V on the power valve plates. Low voltage option is about 317V.
 

mickeydg5

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Your MV controls will not work correctly until you get the amplification stage and power supply node thing worked out. That should be your first priority right now.
 
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RickyLee

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Your MV controls will not work correctly until you get the amplification stage and power supply node thing worked out. That should be your first priority right now.

I have that added master volume inserted right after the treble pot. At this time, it is just attenuating signal as I found a sweet zone setting with it that now allows the PPIMV to sound much better. This little power amp gets slammed hard with audio signal even in stock factory form. I made that issue even worse with two added stages. So I am still tuning the interstages. I did get closer this evening as I had some time to tinker on it. I am getting ready to measure out and document where everything is now at.

Swapping in 6V6 for the JJ 6L6 helped a bit as well as I was playing it at a low volume and it is actually starting to inspire me a bit to play lol. It now has some sweet singing sustain. But still have a bit more to fine tune . . . .
 

mickeydg5

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I am telling you your power supply is priority. No matter what you are doing now could be affected by altering the power supply rail later. You have too many stages on one power supply node. Get the power supply nodes set up for the amplification stages now, then no worries.
 

RickyLee

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I am telling you your power supply is priority. No matter what you are doing now could be affected by altering the power supply rail later. You have too many stages on one power supply node. Get the power supply nodes set up for the amplification stages now, then no worries.

I was going to recap it and I am getting a list to place an order for parts. Have not made up my mind on filtering values for the nodes just yet. I also need 9 pin sockets for another project ect, so will be ordering the new filter caps soon. Just making sure I get everything I need before placing the order - and also waiting for my new billing cycle on my credit card to clear.

:D

I might even drill a hole to accommodate a 2nd dual filter can as this amp has just one dual can.
 

RickyLee

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I am telling you your power supply is priority. No matter what you are doing now could be affected by altering the power supply rail later. You have too many stages on one power supply node. Get the power supply nodes set up for the amplification stages now, then no worries.

This amp in stock form has V1B and phase inverter V2A/B on one filter node. Then the first stage V1A is alone on the last filter node. I tapped my my new 2 stages off that last node that feeds V1A.

Were you thinking I added my two new stages to that crowded middle node?

So yes, I am going to restructure that later when I order my filter caps. I will put phase inverter on its own node, then 3rd/4th stages on next node and then 1st/2nd stages on last node.

I am considering 100uF for power tubes/1st node. Then 16uF node for the screens. Maybe go 32uF for rest of the nodes.
 

RickyLee

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Your MV controls will not work correctly until you get the amplification stage and power supply node thing worked out. That should be your first priority right now.

OK. I made a clip showing where this Studio 15 is at. I left everything set/changes that I did last night. The main thing I accomplished last night was dialing in that pre MV to attenuate signal. So basically that 1MEG log pot is set at about 2 o'clock. And then I just use the original MV/PPIMV. You will hear me turn the bass pot from 0 to 10. Hardly any change. As we have discussed, it is not part of the tone stack and just basically shunts some signal to ground. Higher signal levels will give bassier tone of course.


Gain 6 Treble 5 1/2 Mid 7 1/2 Bass 0 to 10

 
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RickyLee

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Another clip. You will hear me take the Jubilee clipping signal IN/OUT of the circuit. I just found out with this test that the amp does not really need it lol. I had the clipper in there to attenuate some signal and add some bite. But somehow I found a good compromise between all my inter-stages quite easily. And the most important thing is the amp is very fun to play at extremely quiet levels.

Cleans up well rolling down guitar volume which you will hear me do in this clip as well.

 
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RickyLee

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I took some AC signal readings on the Studio 15 power output running this hot rodded channel. Just used my meter at the speaker out jack. This is without the Jubilee clipper in the preamp. Without the clipper I have a huge signal swing of 45VAC at after the phase inverter at the junction of C13/C14. This is a hotter signal going into the power amp than I have even seen on my 2204. I have GT 6V6 which are a supposed old Russian 6L6 variant 6L6 6P3S. My plate voltage went up to 392V. I have them idling at 30mA each side.

My peak AC signal was: 31.7VAC into 16 ohm load output transformer impedance is 16 ohm.
31.7V X 1.98A = 62.8W peak.

27.9VAC into 8 ohm load output transformer impedance is still 16 ohm.
27.9V X 3.49A = 97.3W peak.

Obviously, this is using a voltage meter and it is voltage peaks. Input is my bridge humbucker pickup that puts out just under 300mV. I have the pickup lowered a bit to blend better with the single coil neck/middle.

Would I multiply these numbers out by .707 ti get a better average? And probably need the average numbers instead of the peaks at that output as well?

I was wanting to put the JJ 6L6 back in and do the sane test but things came up today. Will do that another day.

I am also very eager to try a pair of KT66 in this amp.
 

RickyLee

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Would using a resistive dummy load be a way to measure and get a ballpark reading for output power?

Voltage reading across a speaker under load is obviously not giving me a very accurate power reading. Impedance changing with frequency.
 
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