19-05-2024, 12:38 PM
(This post was last modified: 19-05-2024, 12:41 PM by Mike Watterson.)
Ad hoc tests for Diodes & Rectifiers
The only high voltage thing needed is a leakage tester.
Gear
1) PSU for heater/filament. AC or DC
2) Anode power supply. 0 to 30V DC. Less than 50mA. Possibly a wirewound pot on a 12V PSU
3) Leakage tester. Can be made easily from the flash in a single use film camera! Should have 2M Ohm series resistance.
4) DMM to measure Anode voltage.
5) DMM to measure Anode current.
Procedure:
1) Check filament. Resistance is about 1/2 when cold. Power up slowly. Stop if it seems too bright and recheck valve type and spec.
2) Check PIV when heater/filament powered with the leakage tester. Anode volts should be higher than PIV in data as that's a minimum.
3) Check heater/cathode with leakage tester, if it's rated as isolated.
4) Check Anode forward volts/current using LV PSU. Do not exceed current rating. Might be 25mA for a rectifier. If a signal diode does 1mA at 2V, is loads. We only care about the current, i.e. emission. A signal diode is unlikely to be a problem, ever, unless gone to air, bad leakage to heater or no heater/filament. A signal diode only needs about 25V PIV on AM and 40V on FM.
Power rectifiers can go low emission or fail on PIV.
The diode testing applies to diodes inside other valves, such as EBL, EABC, DAF, DAC, EAF etc. Just leave the other electrodes open circuit, though leakage test to diode anode & cathode agains other electrodes is worthwhile.
Semiconductor diodes can be tested with same gear. A 20M Ohm impedance DVM or VVM will display PIV.
I disconnect all metal/selenium rectifiers.
Next is Triodes.
The only high voltage thing needed is a leakage tester.
Gear
1) PSU for heater/filament. AC or DC
2) Anode power supply. 0 to 30V DC. Less than 50mA. Possibly a wirewound pot on a 12V PSU
3) Leakage tester. Can be made easily from the flash in a single use film camera! Should have 2M Ohm series resistance.
4) DMM to measure Anode voltage.
5) DMM to measure Anode current.
Procedure:
1) Check filament. Resistance is about 1/2 when cold. Power up slowly. Stop if it seems too bright and recheck valve type and spec.
2) Check PIV when heater/filament powered with the leakage tester. Anode volts should be higher than PIV in data as that's a minimum.
3) Check heater/cathode with leakage tester, if it's rated as isolated.
4) Check Anode forward volts/current using LV PSU. Do not exceed current rating. Might be 25mA for a rectifier. If a signal diode does 1mA at 2V, is loads. We only care about the current, i.e. emission. A signal diode is unlikely to be a problem, ever, unless gone to air, bad leakage to heater or no heater/filament. A signal diode only needs about 25V PIV on AM and 40V on FM.
Power rectifiers can go low emission or fail on PIV.
The diode testing applies to diodes inside other valves, such as EBL, EABC, DAF, DAC, EAF etc. Just leave the other electrodes open circuit, though leakage test to diode anode & cathode agains other electrodes is worthwhile.
Semiconductor diodes can be tested with same gear. A 20M Ohm impedance DVM or VVM will display PIV.
I disconnect all metal/selenium rectifiers.
Next is Triodes.
