Power Supply

[Amled87]

I'm building a power supply for two 12AX7 tubes. I am wanting to use a 20vAC wall supply, and then use a voltage quadrupler circuit to turn that into 160v. I'll then use a voltage divider to provide 3.2v to the heaters in parallel. Draw for the 12AX7's seem to be roughly 400-500ma. So, a 2A 20v supply followed by a voltage quadrupler and voltage divider to power the tubes and heaters would work?

I've did all the equations for capacitance, would I be able to get adequate power from this circuit? I'll be using 220uf 300v filter caps and 1N4007 diodes.

 

[Brian Roth]

"...3.2v to the heaters in parallel"??? I don't quite follow that.

Bri

 

[Amled87]

"...3.2v to the heaters in parallel"??? I don't quite follow that.

Bri

If the heaters are wired in parallel they call for 6.4 volts. That would be 3.2v to pin 9, and 3.2v to pins 4&5 tied together no? Or would it be 6.3v to pin 9 and 6.3v to pin 4&5?

This is the reason why I'm asking. Any headache I eliminate now means one less when building.

 

[Brian Roth]

It would be a TOTAL of 6.3 Volts applied between pin 9 and 4+5. With the two halves of the filament wired in that configuration (parallel) the GE data sheet says the filament current draw would be 300 mA, so a total of 600 mA for two sets of parallel connected filaments.

Bri

PS, you might consider running the bottles at 12.6 Volts, ie connect power via pins 4 and 5 and ignore 9.

 

[TheJames]

There are effectively two heaters in the 12AX7/12AT7 style tubes. The heaters in series (per tube) would run at 12.6V. The heaters in parallel would run at 6.3V. If you put the series heaters of two tubes in series, you'd need 24-25V (Peavey does this in amps like the Classic 30 and this was commonly done back in tube TV days.) One advantage of running at 12V vs 6V heaters is a halving of the required heater current. It typically takes about 300mA of current at 6V to fire up a 12AX7, or 150mA at 12V.

Typically, one would pick a heater voltage and move on. When you look at common output tubes like 6L6, 6V6, EL34, EL84, they all have 6.3V heaters. Since you already need 6V to make the power tubes happen, most amps will settle on using 6V for all heaters in the amp. One place where this might not apply is an amp with lots of channel switching and relays and such.

If you want to make a power supply for a tube preamp, you'll need a B+ at 2-300V at a few mA, and a 6 or 12V supply at 300 or 150mA per tube with a decent margin. For two tubes at 6V, a 1-2A supply wouldn't be bad.

 

[Amled87]

It would be a TOTAL of 6.3 Volts applied between pin 9 and 4+5. With the two halves of the filament wired in that configuration (parallel) the GE data sheet says the filament current draw would be 300 mA, so a total of 600 mA for two sets of parallel connected filaments.

Bri

PS, you might consider running the bottles at 12.6 Volts, ie connect power via pins 4 and 5 and ignore 9.

I don't have a power supply at all at the moment. What I have is 125v at the wall, I planned to have 125v coming in and then split that two different directions. The first being a voltage divider to produce 12.6v or 6.3v for the heaters. Then, a voltage doubler to convert AC to DC and to get 200-220v for the circuit itself and to power the 12ax7's.

 

[scott2000]

Could maybe even use one of the primaries of a split 120/12v tx to get your 160 B+? Like the PRR compressor?
Something like one of these maybe? Although I haven't looked at the specs?

https://www.digikey.com/en/products...X2IBaJtBBpIWPERAA3YRhwFiZSJTAMaAVhbsukEJIkSgA

 

[Amled87]

There are effectively two heaters in the 12AX7/12AT7 style tubes. The heaters in series (per tube) would run at 12.6V. The heaters in parallel would run at 6.3V. If you put the series heaters of two tubes in series, you'd need 24-25V (Peavey does this in amps like the Classic 30 and this was commonly done back in tube TV days.) One advantage of running at 12V vs 6V heaters is a halving of the required heater current. It typically takes about 300mA of current at 6V to fire up a 12AX7, or 150mA at 12V.

Typically, one would pick a heater voltage and move on. When you look at common output tubes like 6L6, 6V6, EL34, EL84, they all have 6.3V heaters. Since you already need 6V to make the power tubes happen, most amps will settle on using 6V for all heaters in the amp. One place where this might not apply is an amp with lots of channel switching and relays and such.

If you want to make a power supply for a tube preamp, you'll need a B+ at 2-300V at a few mA, and a 6 or 12V supply at 300 or 150mA per tube with a decent margin. For two tubes at 6V, a 1-2A supply wouldn't be bad.

What I'm building is strictly a preamp, so the current required for a power amp stage is null as it'll be ran into the PI/Poweramp of another amp . I'd need either 12.6/6.3v for the heaters and 200-220v for the two 12ax7's.

Would having 125v coming in, splitting the power the first being a voltage divider to get that down to 12.6/6.3v and second a voltage doubler to get 200-220vdc for the b+ for the tubes be adequate?

 

[TheJames]

You're attempting to avoid the cost of the transformer. You effectively have two options...Use a transformer, use some sort of switch-mode PSU to power the preamp. I wouldn't suggest trying to use the mains power directly.

One of these, a handful of resistors and caps, and you're on your way.

https://www.ebay.com/itm/293259273977?hash=item44479d66f9:g:e9cAAOSwUHld8EKs
I didn't dig through the schematic of your DSL40C, but it wouldn't surprise me if the basic signal path of the JCM800 isn't available in that amp already.

 

[Brian Roth]

I think I misread the original post which mentions 20VAC which I ASSumed meant a wallwart. Rereading that first post totally confuses me now.

You need a transformer of some sort for safety.....wallwart or whatever.

Bri

 

[TheJames]

I'll echo Brian's concerns for safety. You need the isolation provided by the transformer with a good ground, properly sized fuse, etc.

Be safe, not dead.

 

[Brian Roth]

This is getting complicated with two different threads covering the same project. :-(

Bri