Voltage for the Valvecaster?

[kristoffereide]

Do you recommend 1/2W parts? I've used 1/4W but its getting weaker and worse sounding as we speak. If I'm really quiet, I can hear it withering just sitting there...

[Ell]

Do you recommend 1/2W parts? I've used 1/4W but its getting weaker and worse sounding as we speak. If I'm really quiet, I can hear it withering just sitting there...

I haven't done the MAX1044 thing yet, but I have standard 1/4W resistors in my standard Valvecaster and I have no issues.

[Harold]

Can anyone tell me what the difference will be with the plates at 40+ volts? More gain or more clean headroom?

I already changed R2 to 110K to reduce the (over)saturated gain so I'd like the Valvecaster to be more "open". I don't need any more gain



Also, how do I connect the higher voltage in this schematic? Pin 5 to 12v and R2 and R3 to 40+v?

[petemoore]

  Look up data sheet, the heater current and wiring allows 12v or 6.3v filament supply.
  The plate supply can be much higher.

[Harold]

  Look up data sheet, the heater current and wiring allows 12v or 6.3v filament supply.
  The plate supply can be much higher.

I know the heaters of a 12AU7 only may be fed 12.6 Volts and that the plates can handle voltages up to 300 Volts. My questions is where do I connect the the 'high voltage' and what will it change?

[lowend]

The heaters are pin 4 and 5. That's about all I can help with. It looks like you would need to change some resistors and capacitors in the rest of it ie actually know what you're doing, rather than be able to just separate the heaters and slap a higher voltage into the rest of the circuit. Or not.

[FunkyGibbon]

Hi Harold,

I believe that connecting as you suggest, attaching your regulated 12VDC to the heaters (pin 5), as well as to the charge pump, and then connecting the output of the charge pump (higher voltage) to R2 and R3, is exactly how it should be done. See the Mesa Boogie V-Twin pedal schematic for a simlar method, except that they just used a single diode to rectify the supply 12V AC before going to the heaters (no regulation!), and obtained the higher voltage for the plates via a transformer and bridge rectifier instead of the charge pump method.

Just watch your voltage ratings on your capacitors.

Christopher

[merlinb]

I know the heaters of a 12AU7 only may be fed 12.6 Volts and that the plates can handle voltages up to 300 Volts. My questions is where do I connect the the 'high voltage' and what will it change?

The higher the supply voltage for the anodes, the greater the headroom, gain and output signal will be. Available overdrive may or may not increase- it's hard to compare with low-voltage operation.

[frequencycentral]

Merlin is right as always. In my experience using a high voltage supply isn't going to give you much of a higher voltage at the anodes unless you use a cathode resistor and bypass cap. You might also want to try reducing the value of R3 until the anode of V1B sits at half the high voltage supply (47k maybe?). The valvecaster's gain control at the cathode of V1A also presents a problem. In addition to being scratchy as you turn it, it will also thunk when you reach close to maximum gain as the cathode becomes grounded. A much better idea would be to use an interstage gain control and fix the gain of V1A with a similar arrangement to V1B: lower value anode resistor, cathode resistor and bypass cap. This will get the anode voltage up where you want it as well as keeping the anode voltage stable.