09-06-2024, 03:46 PM
700V via 4 megaohms is 175 μA into a short. Probably about 140 uA to dry skin. A capacitor charged via 4 M Ohms is not safe. Perhaps the leakage / breakdown sockets should have a spring loaded switch/button that disconnects the supply and puts a 1 K ohm resistor load.
The 175 μA max is 150 μA on a diode or transistor with 100V breakdown (PIV or VCE open circuit base, or VCB). Generally it's non-destructive. Things like a 1N4148 can be selected on test as 120V reference. With capacitors it's simpler to have a series neon with an almost zero leakage capacitor across it. The slow flash speed roughly measures gigaohms. Rapid or apparently solid means the cap is useless in valve set for "tone correction", isolation, g2 decoupling or anode to grid coupling. There is no one "that capacitor". So there will be at least a 3 way switch between the 1/2 HT (about 185V no load), full HT (about 350V no load) and doubler volts (about 700V no load). I might add another stage to have 1000+ volts as some capacitors need that. I'll see if I have a four way switch and stare at my stock on 1μF 400V met-polys! The switch would have 1 M ohm on output. The 350V would have a 1 M Ohm feeding switch, the 700V having 3x 1 M ohm feeding switch. A 1000V range would need 5x 1M or maybe I might have some real HT resistors. I can test really high value resistors for breakdown by DMM in series with 0V and check the microamps are correct.
The 175 μA max is 150 μA on a diode or transistor with 100V breakdown (PIV or VCE open circuit base, or VCB). Generally it's non-destructive. Things like a 1N4148 can be selected on test as 120V reference. With capacitors it's simpler to have a series neon with an almost zero leakage capacitor across it. The slow flash speed roughly measures gigaohms. Rapid or apparently solid means the cap is useless in valve set for "tone correction", isolation, g2 decoupling or anode to grid coupling. There is no one "that capacitor". So there will be at least a 3 way switch between the 1/2 HT (about 185V no load), full HT (about 350V no load) and doubler volts (about 700V no load). I might add another stage to have 1000+ volts as some capacitors need that. I'll see if I have a four way switch and stare at my stock on 1μF 400V met-polys! The switch would have 1 M ohm on output. The 350V would have a 1 M Ohm feeding switch, the 700V having 3x 1 M ohm feeding switch. A 1000V range would need 5x 1M or maybe I might have some real HT resistors. I can test really high value resistors for breakdown by DMM in series with 0V and check the microamps are correct.
