AC Elevated Heaters . . . .

[RickyLee]

if it's similar to the doubler i posted i would make sure you use equal capacitances (really, the same caps so that things like esr are the same) for the "top" and "bottom". 100nf or so film/ceramic cap in parallel to each branch is a good idea as well

Yes, I plan on keeping the C1 C2 same values. The datasheet for the L7806 regulator shows a .33uF and .1uF non polarized cap on each side of the regulator, so I will do that as well. The parts are now adding up and finding space is going to be tough. But this is a good problem to have.

I went with that doubler I posted, as I did not see your drawing till I already got started. Any difference you can think of between the two?

I had initially kept an inline fuse coming off the high positive side transformer 5V tap leg as I was experimenting. I am low on fuses and was initially blowing the fuses I had in there lol. But that had to be from the inrush/powering down discharge spikes. Last fuse I blew was a 1A slo blo. Then I just removed the fuse. It is just temped in there right now. But I had three 12AX7's heaters and relay coil powered/holding and 13.4VDC into regulator and holding 6.01VDC out of regulator. This was with huge caps temped in there of 6600uF / 13300uF (oddball pairings as I had to jumper in odd values I have on hand) and no small film caps in there yet for parasitics.

So I do not see any reason I can not run two 12AX7's and the relay safely at 6VDC and not have to worry about it. I was wanting an inline fuse in there, but as I said before, the space inside is a problem at this point and that huge inline fuse wire will then be mixed in with other sensitive wires and probably adding noise.

I need to try today, running the two 12AX7/relay on this 6VDC and I need to load all sockets up with the rest of the AC heaters draw AND load in a pair of KT66 and then see if I still have my 6VDC lol. The numbers above were with 6V6 and one 12AX7 6VAC socket empty. My AC heaters were at 6.9VAC lol. So that was not pulling down the PT secondary much at all.

 

[RickyLee]

RickyLee, here's the MOSfet switcher solution Mojotone has...
https://www.mojotone.com/kits/MojotoneAmpKits_x/Mojo-Complete-Mosfet-Switching-Soldered-Assembly

That is pretty sweet for sure. And price is decent.

I am still wanting a more complex switching scheme that is beyond just a one footswitch to toggle between A/B channels. I was thinking last night for a somewhat simple way to have 3 channel switching, like the logic control type stuff. I have another amp that was my first one that I installed relay coils on. That one takes a two button footswitch but one switch toggles channels 1/2 while other switch toggles in/out a stage that is upstream of both channels. You somewhat get 4 options there, but you have to toe tap dance to get a certain combination you want lol. Unlike logic switching where one button/switch will give what ever channel/mode you want. Like the JVM 4 channel amps for example.

 

[RickyLee]

@RickyLee
Sorry my head is not screwed on all the way. I forget how we got the voltage higher before exactly but it may have been due to a "+"tolerance transformer, you know putting out more than 5VAC at the secondary.

I just did not adjust for diode drop and gave that 7V number before. In actuality a 5VAC will yield about 5.2VDC with a basic capacitive filtered rectifier at nominal tolerances.

So a voltage doubler as @thetragichero indicated is the way to go if higher DC voltage is needed from the 5VAC secondary.

Why do you not just use the 5VAC for DC supply for relays and switching while adding another DC supply of the 6.3VAC for tube heater(s)?

Reason for trying to remove one or more 12AX7 heaters off the 6.3VAC tap over to the 5V tap was to free up the extra headroom on the 6.3 winding and be able to run my old KT66 stash I drug out. But then also I want to be able to pop in two EL34 later as well. I did not want to push it too much with seven 12AX7 and two EL34 on a 5A heater tap. I always figure 350mA to 400mA per 12AX7, even though the spec is 300mA.

But . . . . last night I was trying to have one of my multi-meters into this crazy experiment to see current draw while my other meter was monitoring voltage. I was running out of test leads as I have a few that were acting up intermittent, so had to abandon the meter inline for current. And I might have had a meter internal fuse issue as well as my circuit was not working right his way. But I thought I was getting a 230mA reading of current on my meter with one 12AX7.

Could their true heater filament draw actually be that far under 300mA? And does that filament draw change while the amp is under heavy load? Then I would think you would have to audition a variety of 12AX7 brands to see what you het . . new production and NOS. I am not sure which tube it was now. It was either the old GE long plate I initially had in V1 or it was a new China 12AX7B or 12AX7C9 lol.

 

[thetragichero]

you definitely want a suitable fuse or there's a good chance you'll be springing for a suitable pt at some point due to a burnt 5v secondary anyway. two tubes and a relay I'm thinking 2a fuse minimum. make sure to have big caps on both sides of the regulator

 

[RickyLee]

Yeah. Fuse is a good a idea as I do not want to toast my new xfmr.

The parts and space are piling up. I still have not tried to figure a way to load all this in there. I might need to build a small separate board and put all new parts on there as tight as possible and it will have to tuck under my main board a bit. Have to put spacers/standoffs then between main board and chassis.

I want to thank you fellas for the learning experience. I want to keep learning and understanding this stuff more, and that is mainly why I keep tinkering really besides the boredom thing. I will end up using this in another project if not in this one so nothing is lost really. It is all good in the end . . . .

 

[mickeydg5]

Reason for trying to remove one or more 12AX7 heaters off the 6.3VAC tap over to the 5V tap was to free up the extra headroom on the 6.3 winding and be able to run my old KT66 stash I drug out. But then also I want to be able to pop in two EL34 later as well. I did not want to push it too much with seven 12AX7 and two EL34 on a 5A heater tap. I always figure 350mA to 400mA per 12AX7, even though the spec is 300mA.

But . . . . last night I was trying to have one of my multi-meters into this crazy experiment to see current draw while my other meter was monitoring voltage. I was running out of test leads as I have a few that were acting up intermittent, so had to abandon the meter inline for current. And I might have had a meter internal fuse issue as well as my circuit was not working right his way. But I thought I was getting a 230mA reading of current on my meter with one 12AX7.

Could their true heater filament draw actually be that far under 300mA? And does that filament draw change while the amp is under heavy load? Then I would think you would have to audition a variety of 12AX7 brands to see what you het . . new production and NOS. I am not sure which tube it was now. It was either the old GE long plate I initially had in V1 or it was a new China 12AX7B or 12AX7C9 lol.

Tube tolerances are +/- 10% but a weak or out of tolerance tube heater could be of higher resistance dropping the current to that 230mA. Check out the multimeter and connections but also the tube may need testing to know if it is good enough. Did other 12AX7 pull the same 230mA current?

With a proper power supply setup, two or three 12AX7 can placed on the 5VAC taps easily.

 

[RickyLee]

Tube tolerances are +/- 10% but a weak or out of tolerance tube heater could be of higher resistance dropping the current to that 230mA. Check out the multimeter and connections but also the tube may need testing to know if it is good enough. Did other 12AX7 pull the same 230mA current?

With a proper power supply setup, two or three 12AX7 can placed on the 5VAC taps easily.

I was already curious and just got done experimenting lol. I had to 86 the one oddball meter and dug out my older Fluke 77 to replace it. My main working meter is nicer newer Fluke.

So I put both meters inline with the heater string in between V3/V4. So the two meters, one on each side of the 12AX7 heaters, are seeing the current draw on each side of last three 12AX7's V3 to V1, healthy tubes. Voltage is 6.4VAC and the current is .94A on each side. Pretty cool. So obviously .94A is the total current as it is AC and you do not add the legs together. That works out well and I will obviously respect the data sheet spec of 300mA a lot more now.



I just always liked rounding up to be safe anyway and always factored .35A to .4A per 12AX7.

 

[RickyLee]

Well, here is a quick clip of this Lil Beast of an amp project. Playing my Super Strat into my Heritage Greenback M20 2X12. Volume is low and you will hear me talking calling out the channels and the EQ on/off on the Boogie side.

2C+ side still does not have that 10pF/3.3M bridge feedback loop installed. I do not gave plans for switching over to the Fender clean layout, so I am still experimenting with that positive feedback loop. I might put it on a switch and then maybe have a 2C+/2C++ option as well, or might get a wild hair and try to make that channel have a Clean mode.

Boogie side Vol I was 7 then Vol II or Lead Drive was 7. Lead Master barely on past 1 and master volume was just cracked at that glitch spot where the volume jumps from off to almost loud lol.

SLO side gain was at 5. MV set low.

With the EQ, these two circuits can sound quite similar. But there is a difference in the upper midrange snarl for sure. And the 2C+ circuit as this honk in the mids that can be cool or it can be annoying, depending on how you dial it in.

My phone is having worst issues than I had thought. The volume is not too distorted, but then the amp volume was just over talking/conversation level. My phone volume is swelling up and down, so that is not the amp lol.

So most importantly, I have never played a real authentic Boogie 2C+ or a Soldano SLO, so I have no idea how close my project is really. And this has some differences, mainly in the loop area. I heard a guitarist play a Soldano SLO in a band that opened up for my band many years ago, and honestly I was not impressed with his tone that night. He played a Gibson Les Paul into his Soldano SLO. He might not have had the amp dialed in to how I would have liked though lol. Odd, as I remember it being very muddy and fizzy too.

Thinking about adding a mode switch on that SLO side that will switch it into a Splawn Quickrod High Gear stage.

 

[myersbw]

Wow! That's some in-your-face style gain, eh? Looks like you have 10...maybe 11 trim pots inside there??? You could also call the the UltraTweak! lol! I'll have to say you used every square inch of that chassis!

 

[mickeydg5]

Sounds mean.
Tapping the EQ almost sounds like kicking in an exciter.

 

[RickyLee]

Thanks fellas.

I found a couple odds and ends last night that I overlooked. First one, on SLO channel after 3rd stage, I forgot to add the 330K grid load. I do have the 2.2M there, which I am remembering is a bit high above 12AX7 spec? Anyway, I messed with a trimmer there last night and I ended up putting another 1MEG there in parallel with the 2.2MEG. It brings down the saturation just a touch. I was already able to turn the gain on that channel to 10 without things getting unstable, which is actually very surprising. Gain was on 5 for the clip. On the real SLO, the Clean channel ties back in right there. I got sidetracked and forgot the 330K. I might have thought I was going to put a trim pot to experiment or add a possible similar Clean channel. Anyway, my 2.2M was under some point to point stuff, so just added in the 1MEg above lol. Still has plenty of dark growl.

I might still add a Clean channel later by diverting around one of the four stages. The 2C+ channel, I still have not added that 10pF/3.3MEG bridge which is also a positive feedback loop.

I also noticed on 4th stage before cathode follower, SLO uses 220K plate and I put a 120K. But maybe I did that on purpose? Dam I can not recall lol. But it might actually be a good move there too as might be helping to smooth things out slightly. Plus, my preamp voltages are a bit lower than Mesa/Soldano spec so all my gain stages are biased hotter. But then this is running in my 400V B+ mode. When I switch to 450V high B+ mode, I am over the Soldano spec on a couple stages and closer to Mesa spec. I set up my power supply B+ rail closer to Mesa 2C+ spec. But that I need to modify later as I have a node that is giving me some high anode voltages on two SLO stages.

SLO 3rd stage has 340VDC on 12AX7 plate and then last 4th stage has 364V on plate then cathode follower has 233V grid and 235V on the cathode. This is all on high B+ mode only. Clip was made with 6V6 in low B+ mode 400V biased up 60% bias idle figuring 14W per 6V6.

Oh yeah, lots of little trim pots, as I might experiment a bit more. Maybe put a fixed value in for those later after fine tuning lol. My lil secret. Don't tell anyone man!

 

[RickyLee]

I was noticing some added noise, 120Hz hum, since I put this relay coil 5VDC circuit in. The noisiest of the two channels before this 5VDC full wave bridge rectifier relay coil circuit got installed was the Boogie side. Actually, the hum was a bit worse, then I put the chassis into its head shell and the Boogie side all hum is gone, only the high gain hiss is there. But now the Soldano side has that hum when before it was quiet even with the chassis out in the open.

I have the relay powered ON for the Boogie channel, Soldano is on the normally closed relay contact, so relay coil state is OFF.

So I pulled tubes, V1A is used by both channels, then SLO goes to V5A, V5B, V6A to V6B cathode follower.

Hum is still there with V1 pulled, but then hum is gone with V5 pulled. Midrange pot increases hum and master volume eliminates it. So at least I got that much sorted. I put every 12AX7, all grounds for each tube/gain stage and its respective filter cap on one ground, then each node section was then ran to the ground buss in order of power supply flow/feed. Then the ground buss gets fixed at the input and that is the only chassis ground point. The power receptacle ground is the only other ground point enviously at other end of chassis.

I put the ground for the relay coil on the screens node ground on the buss, and I had tried clipping that ground in different spots on the buss and even tried on chassis for shiggles, and I heard no ground loops, so I put it on the screens node ground as it was close to the 5V rectifier and that 1000uF smoothing cap.

I should mention, that for now I have the original 5V rectifier smoothing cap circuit back in with just the relay on it. I do not have the caps yet to mess with that voltage doubler circuit for a 12AX7 DC heaters.

I am figuring I need to check this out against a few other production amp models, as maybe this hum is not that bad really. Being the house was silent this late, the noise seems worse lol. But I am also wondering about my 5VDC circuit and its ground point, then I have my AC heaters ground elevated to the screens node.

I will check more in there tomorrow and try checking grid wires and such. It might be as simple as adding some more shielded runs in there.

 

[mickeydg5]

Check connections and wire passage/lead dress.

 

[RickyLee]

@mickeydg5 ; @myersbw ; @thetragichero or anyone else that could be reading this mess of a thread and has some input lol.

I am ordering some parts, as I need some caps for the voltage doubler circuit. I already have the 6V L7806 regulator. Do I need to get some grease and small heat sink as well for this regulator, or is there a better way to mount it or free standing in air bad? It is rated for 1.5A and I will be trying to run at least the relay coil and one or two 12AX7 DC filaments.

Of course, once again this is going to be a where to put it issue. I already figured out a way to get all the components in there for the voltage doubler circuit, but when I get those caps, they might be physically bigger than I am expecting.

I was reading last night that any 6,800uF 35V rating cap will handle up to 2.5A of ripple current. I had planned on using 6,800uF caps.

 

[RickyLee]

Check connections and wire passage/lead dress.

Regarding this hum, I have not done any extensive trouble shooting. But for that voltage doubler circuit to run two 12AX7 DC filaments, I had planned on putting V1 and V4 reverb tube on DC heaters. Since I am suspecting my 120Hz is somewhere in the V5 branch, I am now wondering if putting either V1 & V5 on DC heaters is better? Or is it a bad idea to skip first stage? As in starting out on AC heaters V1 then you have two gain stages following go to DC heaters? Since reverb is not a priority, I could go V1 and then V5 as DC heaters. This will then have almost all SLO stages on DC heaters. If nothing else, it is a good experiment to try lol.

I was thinking the reverb circuit will add more noise issues when installed, no?

I am also looking at the filament wiring runs breaking up my heaters string in this mess, part AC and part DC with more wires to run and overlap.

 

[mickeydg5]

Well if you want 3 preamp tubes and a relay then you will be hitting 1A requiring heat sink.
One tube and one relay is .4A and adding another tube get to .7A on the regulator.

5V Zener for relay?

 

[RickyLee]

I got the 6800uF 35V caps yesterday. They are physically big, but maybe this weekend I can fanagle 'em in there. Putting a bit of spit on there sometimes helps to work it in.



Don't mind me as Captain Morgan came to pay a visit this evening and he said to tell you all: " ARRRGH ME BUCKO"


Anyhoot, only thing I was able to get done blast evening was compare this new 2C+/SlovDonald to that last 2C+ that I went chasing my tail on last year, and you @mickeydg5 had some input on that one as well. You might remember eh?

I compared the amps noise basically and this new one is far and above much quieter than that last one man. So I probably do not have any issues with this new build at this time. But, I still am going to try and see if I can locate and quiet down that 120Hz hummer a bit. She is always at her quietest when her mouth is full. Ahh yeah, it should be a good learning experience trying to isolate the source of that noise.

Something to note: That 2C+ project number 1 has its B+ voltages and preamp node voltages close to the Mesa specs I have found on the innerwebz. This new one is much lower voltage obviously, mainly when in low B+ mode of 400V. And that old Number 1 is quite noisy, as I went off the Silverface Fender ground scheme and then added a Granger relay switching board tapped off the 6.3VAC heaters.