• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

12AX7 tone control with low B+ voltage

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Get 12VDC brick adapter for your heaters. Spare a few extra watts for this module and you can get any high voltage you need..DC DC Boost Converter 8 32V to 45 390V High Voltage ZVS Capacitor Charging Board | eBay

huh, those are $10 shipped via aliexpress.

Gives me ideas. I have some very old stock "computer grade" capacitors -- I'm aware of the warnings that if i just go ahead and hook them up to high voltage as is they might react violently. I'm not sure if i believe the idea of "re-forming" the electrolyte by gradually increasing voltage, but if i wanted to try that, this would work for that.
 
ericj said:
I'm not sure if i believe the idea of "re-forming" the electrolyte by gradually increasing voltage, but if i wanted to try that, this would work for that.
Believe it; it is true. Reforming electrolytics (not the electrolyte, but the oxide layer) is a standard technique used by people working on ancient electronics. The idea is to keep the current low, so little or no gassing takes place; you want all the current to be used in reforming the oxide, not producing gas.
 
... Reforming electrolytics (not the electrolyte, but the oxide layer) is a standard technique used by people working on ancient electronics. ...

Nowadays when TV collectors or vintage tube amp restorers restore such, we essentially gut the old cap cap and stuff it with modern caps. Caps made nowadays are much better (assuming you don't get ones made with the bad stolen cap recipe, but that was ten year ago). If you go to this trouble, get the 105C caps, as they last better.
 
Thanks everyone for the inputs. Since 12AX7 has small plate current, I think my best option is DC-DC high voltage converter suggested by ballpencil.
Now my question is this tone control good enough as a pre-amp? or should I add a pre-amp as attached?
If yes, should the pre-amp leading or trailing the tone control?
Thanks again.
 

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