About Valve testing

[Mike Watterson]

Yes, a higher than expected reading on any old capacitor means leakage.
The leakage tester is very useful for non-electrolytics. For Electrolytics, even 500V, a 30V PSU with current limit is best to check. The leakage is too high if mA, but 10uA may be fine on electrolytics, though totally a fail on other types.

[Mike Watterson]

More on testing HT for the output valve and on Valve rectifiers.
I'm not considering valve rectifiers other than regular HT. Examples not to be considered right now are the boost/efficiency diodes and EHT rectifiers in LOPT/line scan stages and magnetrons.

Not all HT is either from Mains or HT batteries. Some even in 1930s was from vibrator packs, a kind of 6V or 12V powered resonating relay. These fed a centre tapped low voltage primary and the secondary HT winding AC was rectified by a valve, extra contacts on the vibrator, or later by a selenium rectifier. From the latter 1950s to the early 1980s the vibrator was replaced by a pair of Germanium power transistors wired somewhat like a multivibrator. The last use was on some transmitters, such as Russian military ones and the optional 12V unit for the mains powered Yaesu FT101ZD. The last MkIII still had the transformer wires/windings, but a label stuck over the rear panel where the connector was. Earlier valve car radios that used the car battery (earliest ones had their own batteries including HT packs) had a vibrator and often a regular HT rectifier, but some used synchronous packs. Some large PAs with even 4 x EL34 could run off mains or 12V via the vibrator pack. The last valve radios used the car battery (really 13V to 14V when the engine is running) and Germanium power transistors for audio. They used up to +1V grid bias and the ECH83 was simply an ECH81 marketed for 12V.


[Edit: found this lost draft. Probably I had a power cut?]