Building Power Supplies for 2 X 12ax7 pedals

[bcmatt]

~300V is the correct voltage for the 12AX7 in a dumbleator, but using the subminiatures the correct plate voltage for similar operation is much lower, as you know. A 6112 is a bit lower gain than a 12AX7 so you might want to play with values to get it to sound right, but the nice thing about using the subminiatures is you can proper plate voltage without a transformer and AC supply. If I was building I a dumbleator-alike in a pedal i'd reach for subminis first.

I was planning to do the full voltage and a 12ax7 for it since it's supposed to be able to handle alot of signal after the preamp and supposedly one wants the headroom... But it might be worth me trying a 6n17B at lower voltages just for educational purposes... And because I was potentially looking to add some warmth and compression to my SSS.

[mhuss]

Taylor has these cute little modules producing 150-200v from 2-16VDC in. Stewmac is using them in their new "Valve Factory" mini amp kit.

https://www.stewmac.com/electronics/amp ... -1-amp-kit

https://www.shop-tes.com/1363-hvps-vertical-low-noise/

[bcmatt]

Taylor has these cute little modules producing 150-200v from 2-16VDC in. Stewmac is using them in their new "Valve Factory" mini amp kit.

https://www.stewmac.com/electronics/amp ... -1-amp-kit

https://www.shop-tes.com/1363-hvps-vertical-low-noise/

Whoa, those are nice and compact! Definitely handy in tight spaces.

[HeavyTones]

Does anyone know of an smps that can do around 420v? I've been using the C2C ones, but they max out around 370v with 3 6N2Ps.

[bcmatt]

I had to give up my bicolor indicator light on my V1 Cosmodrome in order to ground out the circuit in bypass mode because I'm unwilling to pay for a 4pdt foot switch.
I was willing to add a green LED that glows under the tubes as long as the pedal is powered up though.
Then when the effect is on it just turns on the indicator (right now I have it to the green side of the bicolor but I could switch it to be red by wiring to the other LED anode)
This was an attempt to eliminate noise bleeding through to other random pedals when the pedal is powered up but the effect is off.. but it didn't help. I think it's the cheap switching style wall wart.... Not that there is other options. I'll try filtering the noise at the DC input of the pedal and see if that helps.

I also breadboarded a 6N17B Dumble-ator. There is a certain amount of background hiss when turning up the final recovery output pot. But I can get decent signal to noise by riding the amp master and the first two Dumble-ator knobs higher. I'm wondering if the actual version in the enclosure would be better. I'll upload the schematic once I add all my actual voltages.

20260912_130842.jpg

I feel like it has decent headroom.
I also feel like the bright switch is a bit too excessive to be useful since Martin's tweaked design doesn't lose any top end due to cable capacitance. I'll experiment between 47-150pF

[bcmatt]

Here are my current voltages.
I'm currently running the power off a 12VDC wall wart and a single prefab nixie supply instead of the one from parts in my schematic. It has it's own heater supply that runs up about 6.7V, so that's why I have the big diode that brings it down to about 5.7V.
When I build it into a pedal, I'll just use a bucking converter to dial in 6.3 right from what I'm thinking will be a 9V supply on this one. I'll probably use one of the new UC3843 chips for the supply I have coming because I guess they should be more efficient and less likely to create noise... So I'll have to update the schematic for that too.

20260912_130842.jpg

6N17B Dumbleator.png

[Dr Tony Balls]

There is a certain amount of background hiss when turning up the final recovery output pot. But I can get decent signal to noise by riding the amp master and the first two Dumble-ator knobs higher. I'm wondering if the actual version in the enclosure would be better. I'll upload the schematic once I add all my actual voltages.

I get WAY more noise when i'm breadboarding any circuit. On my prototype tube-muff it wasnt right on the breadboard at all, but built on a boar in an enclosure it was just fine.

[bcmatt]

I get WAY more noise when i'm breadboarding any circuit. On my prototype tube-muff it wasnt right on the breadboard at all, but built on a boar in an enclosure it was just fine.

Thanks Tony. That's a very hope-inspiring message to hear.
I increased the dropping Resisters and dialed up the B+ a bit to 195V and I'll see how that effects things. I'm hoping to get the actual plate voltages a little closer together in the 130-150V range for this tube because that's what I have in my head as the ideal for some reason. This is what I now have:

6N17B Dumbleator.png

It seems to have tonnes of headroom.

I was just trying it with my DC30. It's interesting to learn that the EF86 channel is not distorting in it's own pentode, but it hits the PI pretty hard and is actually causing the distortion there... so with the Dumbleator in the loop, I can slam that EF86 into the Dumbleator's two triodes cranked pretty high and still pull down the "recovery output" and it keeps the amp very clean still. The dumbleator is even a handy tool to see where the distortion is actually created in some of my amps...

[bcmatt]

Trying a different approach with wiring this one:

20260915_074453.jpg

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[bcmatt]

Just finished wiring it up and dialing voltages. Will try it tomorrow since it is midnight now.

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[bcmatt]

For unfortunately my point to point Nixie Supply is not working out so well I dial it in to about 195 volts but it just slowly drops the B+ over the course of a couple minutes down to maybe 160 V which also puts the actual plates down around 100 volts. Anyways I'm not sure what is causing the problem that it keeps dropping volts as it warms up.

20260917_124740.jpg

[bcmatt]

Well, I've learned I need to build and test the voltage booster externally before installing in the enclusure. Also, if I make another attempt at building one point-to-point, I won't bother with the socket and solder right to the IC.
I got frustrated enough trying to troubleshoot, I ripped it out and just installed the PCB booster I had on my breadboard.
I also don't think the full ground rail for the power section is helpful.

I'll have to explore the limitations of this 555 style booster.

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[bcmatt]

Just an update. That Dumble-ator needed a little more filtering and seems to be much quieter now. I noticed I can't ride the Master Volume on my SSS too crazy high or it will clip the first stage. Below about 7 seems fine... And there is tonnes of clean signal that it can put out to the PI still. Anyways, I haven't gotten to play it tonnes yet, but it seems pretty solid now. I'll have to update the schematic...

I'm building a new iteration of the Cosmodrome (X-treme
Tone). Still have the Power supply left to build.

CosmodromeV4.3.png

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20261002_193918.jpg

[R.G.]

I had to give up my bicolor indicator light on my V1 Cosmodrome in order to ground out the circuit in bypass mode because I'm unwilling to pay for a 4pdt foot switch.

Use a relay. Put a Panasonic TQ-2 9V DPDT on the effect circuit board. This can make the effect itself be internally self bypassing with only a single pole of an external switch. They're about $3.

[bcmatt]

I had to give up my bicolor indicator light on my V1 Cosmodrome in order to ground out the circuit in bypass mode because I'm unwilling to pay for a 4pdt foot switch.

Use a relay. Put a Panasonic TQ-2 9V DPDT on the effect circuit board. This can make the effect itself be internally self bypassing with only a single pole of an external switch. They're about $3.

Thanks, RG. This could come in really handy for future builds