Powering the tube driver

[MohiZ]

This is a quick question:

Is the voltage in this supposed to be AC or DC? I don't understand the schematic in the power module section. I tried this with a 12 volt AC adapter, but got hum and a choppy kind of fast tremolo sound (50hz from the AC?). I suppose there's no way to use this one with the AC adapter, so should I get a 12 volt DC adapter?

http://www.generalguitargadgets.com/diagrams/tube_driver_sc.gif

[petemoore]

 First mains voltage [be very careful to unplug before working on] on the transformer primary becomes the 12vac secondary transformer output.
  This is used to heat the tube 12v filament.
  The audio circuit requires DC, the secondary output ac12v is converted to DC [diodes], filtered [caps and resistors] This DC potential is used for ac-signal amplification.

[MohiZ]

The filtering didn't seem to be enough to filter the power line hum out of the sound. Would it be possible to use the 12 V AC just for the tube heater and use a 9V battery to power the rest of the circuit? How is this typically done in tube pedals?

[the_stig]

I would not recommend it.

1) most of the tube drivers out there run on 24VDC. however, there are some that run on 9 volts, but they are said not to sounds as good. changing the voltage would also require some changes to the circuit.
2) if you manage to hook this up to a 9 volt, expect minutes of play time at most. tubes are power hungry.

[george]

This is a quick question:

Is the voltage in this supposed to be AC or DC? I don't understand the schematic in the power module section. I tried this with a 12 volt AC adapter, but got hum and a choppy kind of fast tremolo sound (50hz from the AC?). I suppose there's no way to use this one with the AC adapter, so should I get a 12 volt DC adapter?

http://www.generalguitargadgets.com/diagrams/tube_driver_sc.gif

A 12V AC adapter (applied to points 4 and 5 on the schematic) works just fine - you should be getting 28-30V DC between V+ and V-.  In practice a nominally 12V AC adapter outputs 12.5 - 13V and will come down to about 12V when connected.  If you try to use 9V DC on the whole circuit it probably won't work because the tube won't bias correctly.

Check the soldering everywhere in the circuit. In particular check the orientation of the diodes and the filter caps in the power supply section because it sounds like you have a  problem with the filtering.

[MohiZ]

I was actually playing with this on breadboard. I measured my AC adapter (it's rated "10 - 12 V") and it showed as much as 14 volts unloaded. I did in fact connect the 12 V adapter to the points 4 and 5, but even with the 470u caps there was this kind of a tremolo effect that increased with gain. I guess this could be the result of the parasitic properties of the breadboard itself, because there's so much current going on, huh?

[petemoore]

  Tubes and power supplies.
  Getting the tube to 'work' is a little trickier than transistor.
  Getting tube powers supplied provided in 'pure DC' form for low noise is the 'hard part'.
  Since you don't like that power supply for noise problems...
  I'll just go right ahead and redesign that.
  Start with a 'more workable' plate voltage, <24v and it starts sounding 'lit up', still starved plate sound, just has 'more in the middle' [seems to accept greater input levels without blatting, output goes up, the distortions right there but has headroom enough to make it easier to press on it without it 'collapsing'.
  Let's say you found a DC adapter, enough ma. for the heater, regulators and plate supply. and ___?
  say it has >24dc unloaded, you Regulate using 7812 or 7912 regulator/filtercap, light the filament with it, it drops to a loaded 26v.
  You find out that about the time the filament lights, something smells like burning dust, you touch and burn your sensors on the regulator, put a heatsink on it, then put a bigger heat sink on it, this heat and the filament draw the 'big' current flow from the adapter.
  Now you have your filament supplied with Reg'd/filtered DC.
  Now you can regulate the 26v to 24v [the regulator eats a couple volts] using anyones favorite or the LM317 regulator/filtercap, set for lowest voltage drop [IIRC that jumpers/eliminates the 5k pot], it'll provide a very stable and pure plate supply voltage.
  Obviously there are other ways to work around the power supply problems, some more effecient than this, if you have a suitable adapter [see printers for 'hv' WW].
  It's kind of fun to have easy access to the main circuit supply line, the 7812 will light filament @12vdc unless it's supply drops below 14v [I like to start with at least 3v more for extra margin]. So anything between 15vdc [loaded] and 40vdc [pushing the limits of the regs @38v] gives the regulators room to work with, then you can hear the tube 'open up' and decide what plate voltage offers the preferred benifits the experimental results found to be most suitable for your application.
 

[MohiZ]

Thanks for the great answer petemoore! I'll definitely put that behind my ear (is that a valid figure of speech in English?).

However, it seems that in my case the noise was, after all, NOT created by the power supply, because now that I tried it again it worked without the hum and tremolo effect. I hate intermittent problems  I'm guessing that it was either the breadboard causing some parasitic effects, or my gain pot was faulty (basically the only change I made, and it would make sense, because the tremolo effect got worse when increasing gain).

But anyway now I'm in the clear about the schematic. The tube Driver Didn't have enough gain for me, though, so I'm gonna be looking for another tube distortion to try out.

[george]

  Since you don't like that power supply for noise problems...
  I'll just go right ahead and redesign that.

Granted MohiZ wants to now go ahead with a different design, but ...  I really don't understand why you would need to do this.  I built a Shaka Tube which has the exact same design of power supply, and it has very little noise.

  Start with a 'more workable' plate voltage, <24v and it starts sounding 'lit up', still starved plate sound, just has 'more in the middle' [seems to accept greater input levels without blatting, output goes up, the distortions right there but has headroom enough to make it easier to press on it without it 'collapsing'.

Sure it could be good to have a variable plate voltage, but, I don't get any of that stuff either .... in fact you can get a pretty good low-gain sound (at least with a Shaka Tube).   Anyway if you reduce the plate voltage, don't you reduce the headroom???

Cheers

[petemoore]

I'll definitely put that behind my ear (is that a valid figure of speech in English?).
  Works for me...never heard it before, "I'll put it behind my ear !"
  George wrote:
  Sure it could be good to have a variable plate voltage, but, I don't get any of that stuff either .... in fact you can get a pretty good low-gain sound (at least with a Shaka Tube).   Anyway if you reduce the plate voltage, don't you reduce the headroom???
  First off sorting out AC / rectification / filtering is a 1rst order of business.
  Since there seemed to be confusion about the ps...
  Is the voltage in this supposed to be AC or DC? I don't understand the schematic in the power module section. I tried this with a 12 volt AC adapter, but got hum and a choppy kind of fast tremolo sound (50hz from the AC?). I suppose there's no way to use this one with the AC adapter, so should I get a 12 volt DC adapter?
  ..and it sounded like an adapter purchase choice was about to be made...
  I suggested start with enough AC voltage to rectify/filter/...and regulate [I like the LV tubes having regulated supplies...not sure if it's a benefit over AC on the heater plates, I know it improved performance over WW plate supply when I tried it.
  Starting high voltage and regulating to a lower voltage is always an option [heatsinking may be necessary for larger V drops].
  And then..yes ! Low voltage tubes can be made to behave nicely at various voltages.
 
   

[george]

And if you replaced the PS with a 24V DC supply, you would eliminate the PS section of the circuit as the problem ..