21-04-2023, 07:12 PM
(This post was last modified: 21-04-2023, 07:17 PM by Mike Watterson.)
Not the maximum possible, but note voltage drop (i.e. applied HT) at rated current. If you can't reach rated current or the voltage drop is much higher than desired, then the emission is low.
A flash-gun based or similar capacitor leakage tester that uses a flashing neon (dark = OK, slow flash rate is G Ohms) for AK reverse when heater running and also H-K isolation. These usually have 1M to 2M series resistance. Some old capacitor meters had a leakage test built in.
The HK test and the PIV should be done with rated heater voltage or current and valve warmed up. Some only fail on HK leakage when hot. Not sure of effect on PIV. If vacuum is not so hard or other contamination or physical shock damage are reasons for low PIV.
I've used a 20M Ohm input DMM on volts to non-destructively measure Ge and Si diode PIV as well as Vce and Vcb breakdown (avalanche effect). You can use a select on test 1N4148 or other diode as a low current Avalanche regulator. In contrast the breakdown of K A reverse of tube is flash over and H-K is leakage. A sufficient series resistance as used on semiconductor PIV non-destructive tests is non-destructive. Most valve rectifiers ought to never light the neon even infrequently even with a 400V supply via 2M Ohm. I replace the typical flash 300uF with a 1uF 600V and 2 x 1M in series to + terminal for DUT. The return - terminal of DUT is a neon with a 0.1uF polyester 250V in parallel. The 2M and 0.1uF is a fast enough rate with a short to look solidly on.
A flash-gun based or similar capacitor leakage tester that uses a flashing neon (dark = OK, slow flash rate is G Ohms) for AK reverse when heater running and also H-K isolation. These usually have 1M to 2M series resistance. Some old capacitor meters had a leakage test built in.
The HK test and the PIV should be done with rated heater voltage or current and valve warmed up. Some only fail on HK leakage when hot. Not sure of effect on PIV. If vacuum is not so hard or other contamination or physical shock damage are reasons for low PIV.
I've used a 20M Ohm input DMM on volts to non-destructively measure Ge and Si diode PIV as well as Vce and Vcb breakdown (avalanche effect). You can use a select on test 1N4148 or other diode as a low current Avalanche regulator. In contrast the breakdown of K A reverse of tube is flash over and H-K is leakage. A sufficient series resistance as used on semiconductor PIV non-destructive tests is non-destructive. Most valve rectifiers ought to never light the neon even infrequently even with a 400V supply via 2M Ohm. I replace the typical flash 300uF with a 1uF 600V and 2 x 1M in series to + terminal for DUT. The return - terminal of DUT is a neon with a 0.1uF polyester 250V in parallel. The 2M and 0.1uF is a fast enough rate with a short to look solidly on.
