Building Power Supplies for 2 X 12ax7 pedals

[bcmatt]

I have a few tube circuits I'd like to build in a large pedal format:
1) A Hot Cat Gain Channel preamp (Bad Cat Xtreme-Tone)
2) A Dumbleator style loop pedal
3) Matchless Hot Box
4) Maybe some others circuits in the future

But I'm definitely determined on the first 2 and have a couple friends that I may make some for too... but the transformer pricing can get a bit crazy, so I am not going to go with the original transformer approach with 120V primaries and 6.3V and High voltage Secondaries.
Also, I'm in Canada, so certain websites are also pretty crazy pricing for shipping for trying to find Toroidal Transformers... but I am tempted to try that approach.

I'm still trying to decide between two approaches and could use some wisdom even about whether these transformers would work or if someone knows other reasonable sources:

A) Work off of a 12VAC Power supply.

For the Preamp style pedals I'd probably lean toward a 12VAC wallwart (but these seem to actually cost about $23 even for anything on Amazon):
https://www.be-electronics.com/ProductD ... 1&CartID=2

For the Dumbleator that would sit on the amp, I'd probably want to keep the source voltage transformer in the actual dumbleator box. Maybe this would do the trick for about $14? (115V, 12VA, 12.6V C.T. @ 1.0A):
https://www.be-electronics.com/product_p/164g12.htm

Actually, I'm under the impression that the Dumbleator could get away with one half the size since it is just one tube, I'm guessing the lighter 164F12 (115V, 6VA, 12.6V C.T. @ 0.5A)would do the trick, but the cost is about the same at $13:
https://www.be-electronics.com/product_p/164f12.htm


Either way the idea would be that I rectify and regulate the heaters in series to about 12 - 12.6VDC

Then, I'm wondering about something like this to also feed in reverse off the 12VAC (or 12.6VAC) right into the secondaries of this for about(115/230V, 5VA, 10V C.T. @ 0.5A):
https://www.be-electronics.com/ProductD ... 0&CartID=1

183F10.pdf

I would then need to rectify and filter the HT off of the primaries to hopefully get my plate voltages...or would that not be a big enough transformer to do the job?

Looking at a post about building 2-tube pedals here:
https://el34world.com/projects/tube_box_3.htm
he uses a toroidal transformer that is only rated at 1.6VA... is that right?


The other Approach:
B) Work off of 12VDC and use SMPS power supplies like talked about here:
https://forum.pedalpcb.com/threads/tube ... its.10652/
I haven't begun pricing out this approach yet, but it seems like it is lighter and cheaper maybe?

[Stevem]

I was into building tube stomp box’s some 3 decades ago.

If I recall right I used two of the same type of 13 dollar Radio Shack transformers .
The first one took 120 down to 6.3 or 12.6 and then that was sent into the secondary of the other transformer to get the B+ voltage.

I put the power supply in a separate 5 X 7 Hammond box and made up a 5 pin XLR cable into the main stomp box .

I think I used a 12BH7 for reasons that escape me now.

[jbrrrrr]

Check out the power supply that C2C Electronics uses for their PCB pedals.

[bcmatt]

I was into building tube stomp box’s some 3 decades ago.

If I recall right I used two of the same type of 13 dollar Radio Shack transformers .
The first one took 120 down to 6.3 or 12.6 and then that was sent into the secondary of the other transformer to get the B+ voltage.

I put the power supply in a separate 5 X 7 Hammond box and made up a 5 pin XLR cable into the main stomp box .

I think I used a 12BH7 for reasons that escape me now.

Oh, that's super cool! I'm intrigued. I imagine a bit of money and size could be saved on the second transformer since it deals with much lower current for the high voltage B+.
So, when you say that the power supply was kept in a separate box, do you mean both the transformers, or just the one stepping it down sort of like a wallwart?
What was travelling over the XLR? The AC voltages or the Rectified voltages?

[bcmatt]

Check out the power supply that C2C Electronics uses for their PCB pedals.

Cool, thanks! They look to be sold out, but they have the schematic and parts list which is handy.
Just found this other one, but you don't get any info about it till after you by it:
https://frogpedals.com/index.php/produc ... ndle-of-5/

[xtian]

I'm happy with the SMPS I used in my Black Butte models.

Here's the listing on Amazon: https://www.amazon.com/dp/B0D9VCYBLB

And here is my build log: https://ampgarage.com/forum/viewtopic.php?t=38680

[jbrrrrr]

Cool, thanks! They look to be sold out, but they have the schematic and parts list which is handy.
Just found this other one, but you don't get any info about it till after you by it:
https://frogpedals.com/index.php/produc ... ndle-of-5/

I've used the C2C one both as part of their self-contained PCBs, and as the standalone PCB for just the power supply and can confirm it's a great little guy that can power 2 small preamp tubes pretty comfortably as long as you're not trying to get too far above 250-300VDC. Anything past that and you might need to step up to a bigger solution. I'm sure it's probably not the most ideal way to generate B+ safely, but it does work... esp. if you can run the heaters off 12VDC in directly and skip the 6.3VDC output it gives you, and power the PCB off 12VDC so all you're really pushing it for is the B+ step up, and not heater regulation also.

Edit: that Frogpedals one looks roughly about the same design, although hard to say without seeing the parts list - it does look like it includes a fuse at least, which C2C's doesn't on the board. I'd bet they're both using the same 555-based idea.

[bcmatt]

I'm happy with the SMPS I used in my Black Butte models.

Here's the listing on Amazon: https://www.amazon.com/dp/B0D9VCYBLB

And here is my build log: https://ampgarage.com/forum/viewtopic.php?t=38680

Oh! That is cool! Sweet Build! That gives me all sorts of GAS

How would that compare with using this board from a 12VDC wallwart:
https://www.amazon.ca/Voltage-Converter ... 5d6c471c52

[bcmatt]

I'm realizing that It's not necessarily the same solution for each of the projects.

For example, looking at the X-treme Tone pedal (Hot Cat Preamp), it wants a lower 235VDC right from the Rectifier and wall votage direct in is maybe less desirable at the pedalboard:

Bad Cat X-treme Tone Schematic.jpg

But then, because it is a pedal, I probably want to use the 12VAC wallwart option, and then something like the Hammond 183F16 Transformer for the HT(115/230V, 5VA, 16V C.T. @ 0.31A) ($13):
https://www.be-electronics.com/product_p/183f12.htm

So, because we are thinking a wall wart solution, I could also consider a 12VDC 1amp wall wart and maybe this would work for both the heater and the HT ($23)?
https://www.amazon.ca/Voltage-Converter ... iewsAnchor
Supposedly the rectification is already dealt with and I'm ready to filter and feed.

[xtian]

How would that compare with using this board from a 12VDC wallwart:
https://www.amazon.ca/Voltage-Converter ... 0DWMBB7FT/

It's cute! Seems to have enough current. Only way to find out is to prototype!

[GAStan]

Check out the power supply that C2C Electronics uses for their PCB pedals.

Cool, thanks! They look to be sold out, but they have the schematic and parts list which is handy.
Just found this other one, but you don't get any info about it till after you by it:
https://frogpedals.com/index.php/produc ... ndle-of-5/

EVERYTHING indicates "Sold Out". He has a notice that he's away for a bit and ordering is turned off on the website, that must be how he turned off ordering. Hopefully everything will show "In Stock" once he returns.

[chaccmgr]

Have you ever thought of using a voltage pump for the HT? I built a bass preamp years ago with two 6N17B pencil tubes (4 triode-systems in total).

PSU: Wall wart 12VDC, directly heats the tubes with 12V, worked fine (Ih=600mA for 2x 12AX7, Ih=800mA for 2x 6N17B)

HT: 12V feeds the voltage pump, resulting in roughly 200V-250V HT (I don't remember the amps but it was enough for 2x12AX7, the higher the voltage the lower the amps). Mine worked with 220V which is what the 6N17B want to see.
The HT will of course be lower than the usual 300V.
Ia=~2-3mA for 2x 12AX7, Ia=~7mA for 2x 6N17B)

So you get away with a 12V/1A WallWart

this way, you don't need bulky and expensive transformers, the pedal stays small and lightweigt (everything did fit into a Hammond 1550M)
parts are relatively cheap. I made a pcb for the entire preamp incl. voltage pump, but if you prefer point to point, I would recommend buying a voltage pump module or kit off the shelf as this take too much real estate point to point, you need a transistor, an NE555 chip, no fun to do PTP.

sorry for some German in the picture...
Heizung = heaters
ohne Gewähr = no warranty, build at your own risk

[bcmatt]

Have you ever thought of using a voltage pump for the HT? I built a bass preamp years ago with two 6N17B pencil tubes (4 triode-systems in total).

PSU: Wall wart 12VDC, directly heats the tubes with 12V, worked fine (Ih=600mA for 2x 12AX7, Ih=800mA for 2x 6N17B)

HT: 12V feeds the voltage pump, resulting in roughly 200V-250V HT (I don't remember the amps but it was enough for 2x12AX7, the higher the voltage the lower the amps). Mine worked with 220V which is what the 6N17B want to see.
The HT will of course be lower than the usual 300V.
Ia=~2-3mA for 2x 12AX7, Ia=~7mA for 2x 6N17B)

So you get away with a 12V/1A WallWart

this way, you don't need bulky and expensive transformers, the pedal stays small and lightweigt (everything did fit into a Hammond 1550M)
parts are relatively cheap. I made a pcb for the entire preamp incl. voltage pump, but if you prefer point to point, I would recommend buying a voltage pump module or kit off the shelf as this take too much real estate point to point, you need a transistor, an NE555 chip, no fun to do PTP.

sorry for some German in the picture...
Heizung = heaters
ohne Gewähr = no warranty, build at your own risk

Well, I ordered this and see what it can do from a 12VDC wall wart:
https://a.co/d/02PC7Dho

nixie suppply.jpg

I think it is considered a SMPS and not a Voltage pump though. I haven't decided if I would use the 6.3V output or if I'll just run the Heaters straight off the 12VDC input from the wall wart... but I'll see what I can get for the HT.
One thing I'm still confused about is whether something like this changes the amount or type of filtering needed on the B+ rail.

For example, would I still dial the Nixie Supply to hit 235V and then filter through the 22K resisters (with 47uF, 33uF and 22uF filter caps to ground) before hitting the plate resisters of the 12ax7s or do I reduce those to 1K resisters and dial down the source voltage?
I feel like I also read somewhere that I may want to parallel some .1uF film caps with the electrolytics to help deal with High frequency noise that a SMPS can cause?

Bad Cat X-treme Tone Schematic.jpg

[bcmatt]

Because the other "pedal" I want to build right away is Martin's improved Dumbleator:

Dumbleator_Update_MPM.png

This would sit on an amp, so it really doesn't need to be pedal shaped, but I think I'd like to go more compact than a rack unit...
Maybe something like this enclosure that is just under 10"x5"x2":
https://a.co/d/05VCbNm0

I also want to see if I can get the transformer cost down from the 262A12 at about $48, even if I am still coming right from 120VAC wall power right into the enclosure:

I'm thinking for the single 12ax7, this may be enough to initially convert the wall voltage(please correct me if I'm wrong):
https://www.be-electronics.com/product_p/164f12.htm
(115V, 6VA, 12.6V C.T. @ .5A) -$13
I would feed the Heaters off of that, and then also to the secondaries of this transformer to produce the higher B+ voltage:
https://www.be-electronics.com/product_p/162f12.htm
(115/230V, 6VA, 12.6V C.T. @ .5A) It's the same as the first transformer but with the 230V primary option. so it's a couple bucks more at about $15.
They are both less than 1/2 pound each and about 1.3 inches in height.
The question is then whether there is an issue with having two transformers in an enclosure where they both lay flat. Do you try to separate them quite a bit?
In the end, this only saves about $20, but is it an improvement by spreading the weight around, or is potentially causing other issues?

[Dr Tony Balls]

Not quite the same thing but it's food for thought. I've been building pedals with subminiature tubes and using a "nixie" type power supply for the HT (~100V). Two 6.3V filament tubes will run just peachy off a 12VDC supply. I did that with my tube muff:





And if its a single 6.3V tube you can use a normal 9VDC supply and a 6V regulator: