High Voltage Power Supply

[Tassieviking]

Mike, are you using 9V or 12V into the HV smps and can your supply provide enough amps ?
I was thinking of doing a Rob amp myself with the power amp in it's own separate box.
I was going to try a single ended amp with one 12AT7 tube running it, not much output but if it works I will be happy.
I was going for the single ended amp because I can easily calculate the impedance VS volts easily.
I am a newbie working out values in valve amps, I only ever worked with valves in industrial machines.
Its the first schematic in this article:

 

[Mike McLane]

I wish I could say I was a newbie. I have NO electronics background. I'm using Sushibox's SMPS and Vig398 speculated that 30mA was near the top end of its current capacity. I'm guessing that this tube tandem and circuit are easily requiring over 20mA and when you get to the outer reaches of an SMPS's current capacity voltage drops off a cliff. As best I can tell this is probably what's going on. Failing any alternative "solid state" solution it appears the tried & true, big & bulky, weighty & costly power tranny is the only way home.

 

[Creach]

I wish I could say I was a newbie. I have NO electronics background. I'm using Sushibox's SMPS and Vig398 speculated that 30mA was near the top end of its current capacity. I'm guessing that this tube tandem and circuit are easily requiring over 20mA and when you get to the outer reaches of an SMPS's current capacity voltage drops off a cliff. As best I can tell this is probably what's going on. Failing any alternative "solid state" solution it appears the tried & true, big & bulky, weighty & costly power tranny is the only way home.

Hello Mike McLane,

You could do the jcm800 micro power amp (from Rob's website), and simply plug a 5751 instead of the 12ax7 if you want less gain from the phase inverter.

 

[Tassieviking]

Another option would be to run the power amp at less voltage, but I am pretty sure you would have to run a different impedance tap on the transformer.
I haven't read up on how to calculate that yet myself, maybe someone else can help you out there.

 

[Creach]

Or use Cathodyne like the Marshall jtm1, it have lower B+, like that you have one triode in front of the phase inverter.

 

[Tassieviking]

Here is more info on the HTM1 build that Creach showed above.

 

[Tassieviking]

Depends on the amp, but potentially. I have one running a 3W amp right now and it's doing great.

Would it be possible to see the schematic for the power amp you are running on the HV PCB ???
Since a few of us would like to try making a pedal power amp it would be great if you shared it, even greater if you had a PCB we could buy.
I can easily make up a PCB if I have the schematic but if you publish it with a PCB for sale I prefer buying the PCB, it feels like the right thing to do.
Cheers
Mick

 

[Mike McLane]

Mike, are you using 9V or 12V into the HV smps and can your supply provide enough amps ?

I'm using a 9V-1.7A PSU. In checking on the 12AT7 & 12AU7 I come up with 300mA each for heaters + 20mA (12AU) + 10mA (12AT7) = 630 total. I can't tell from looking at the Sushibox HVPS where the current supply for the heater(s) comes from. I assume from the "VIN" as shown in his schematic. If so then then all the 250v feed needs to supply is 30mA. VIG398 surmises the max current for the circuit is around 30mA. If so that could explain the sharp drop off of the voltage output as my understanding is that if you need 30mA of steady current your PSU should be sized significantly larger in order to avoid the voltage drop off. How 'bout two HVPS's. . .one for each tube? They don't appear to be "electrically connected" (in the schematic I submitted above) so it's not as if you're trying to hook up two SMPS's in series (which is a "no go")

 

[Tassieviking]

The 12AT7 can go up to 15mA in JJ's datasheet, but then we are talking about the limiting current.
I would think that an amp that is warming up and no signal it should not pull much at all on the HV, when max signal is applied it would increase the mA but not all the way to the max mA the tube could handle.
It would be a really bad design to run any component to its limit.

 

[vigilante398]

Would it be possible to see the schematic for the power amp you are running on the HV PCB ???
Since a few of us would like to try making a pedal power amp it would be great if you shared it, even greater if you had a PCB we could buy.
I can easily make up a PCB if I have the schematic but if you publish it with a PCB for sale I prefer buying the PCB, it feels like the right thing to do.
Cheers
Mick

The power amp isn't running off the HV PCB per se, it has the SMPS built into the same board. I don't like stringing multiple PCBs together in one box when it can be avoided. I'll dig through my files and see if I can find the schematic, I built these quite a while ago. I used it for bass so it uses a hefty output transformer, but that could be swapped for something smaller if you don't need a frequency response down to 30Hz.

I'm using a 9V-1.7A PSU. In checking on the 12AT7 & 12AU7 I come up with 300mA each for heaters + 20mA (12AU) + 10mA (12AT7) = 630 total. I can't tell from looking at the Sushibox HVPS where the current supply for the heater(s) comes from. I assume from the "VIN" as shown in his schematic. If so then then all the 250v feed needs to supply is 30mA. VIG398 surmises the max current for the circuit is around 30mA. If so that could explain the sharp drop off of the voltage output as my understanding is that if you need 30mA of steady current your PSU should be sized significantly larger in order to avoid the voltage drop off. How 'bout two HVPS's. . .one for each tube? They don't appear to be "electrically connected" (in the schematic I submitted above) so it's not as if you're trying to hook up two SMPS's in series (which is a "no go")

Separate SMPS for each tube is definitely a reasonable option. The amplifier mentioned above is a stereo headphone amplifier with a separate 3W power supply for each channel, and I use a separate SMPS for each channel to make sure I'm getting enough juice. That being said I also used 12BH7 for the power section, and it's only 11.5mA per triode on the HV rail so it doesn't pull as hard.

 

[Tassieviking]

I used it for bass so it uses a hefty output transformer, but that could be swapped for something smaller if you don't need a frequency response down to 30Hz

It sound just perfect for what I want, my Ashdown ABM500 is the only bass amp I have at home at the moment and it is just a little bit to big for indoors (so I have been told).
I think a small versatile amp I can use with pedal preamps will suit me just perfect for guitar and bass at home, I might have to make some small cabs though to go with that setup.

 

[HousTom]

Building my own thing using the C2C HV PS and also the C2C 12AX7 (Left) daughterboard. Problem is the daughterboard has no connection at all to Pin 9 of the tube! Which I'm gonna need in order to run the heaters using 6VDC, right? Obviously I can kludge something but wasn't expecting to have to. Amicrazy?

 

[vigilante398]

Building my own thing using the C2C HV PS and also the C2C 12AX7 (Left) daughterboard. Problem is the daughterboard has no connection at all to Pin 9 of the tube! Which I'm gonna need in order to run the heaters using 6VDC, right? Obviously I can kludge something but wasn't expecting to have to. Amicrazy?

Correct, the C2C daughter boards do not have a pin 9 connection because all of the C2C designs run the tube heaters at 9-12V, I don't like running them at 6V.

 

[Tassieviking]

I think it would be better to run the heaters at 12V if possible, it's amazing how much voltage drop you can get in a normal PCB copper trace.
Running at 6V you carry twice the amps compared to 12V and it is the amps that cause the voltage drop (without getting too technical guys)
It might just be mV but converted to a percentage it can be noticeable.
It is easy to find pin 9 on the tube PCB, it has no copper track going to it and it's next to the LED, just run a small wire from it if you want to use it.