Re: Measuring half wave voltages on Valve Testers.
Bill, I reckon from the answers you've received, and the heaps & heaps of banging-on that myself & others have done over the years, that you can be confident in using a Taylor 45 or an AVO VCM or CT160, or a Mullard. They'll all test valves reasonably well if they are up to cal.
Please don't worry about the theoretical RMS values of the sinewaves & half sinewaves used. As long as the Manual's calibration procedures are followed, these AC testers will plod on for years - giving good results. As you will see from Craig's post concerning AVO's patents, a helluva lot of maths is concerned. When you think about it - the valve under test is only subjected to passing Ia during the 10mS of the positive halve cycle using 50Hz. But even then, only at the crest of the waveform, does the full potential effective peak Ia flow. Two or three mS at the most. If we all had stupendous eyesight we could see the valve tester's meter's needle vibrating 50 times a second. Hence its best to study the waveforms using a scope. To delve into the maths of "crest factor" involves a serious amount of calculus.
As David & others have said many times, Taylors & Mullards are great at screening out duff valves in your collection. A "Green Zone" reading will suffice for any valve being used from 1920's TRF's up to thumping big radiograms of the 50's. However, if you're a serious audio amp designer, then the ability of an AVO VCM to tabulate Ia against Vg is what you need.
I've said this a million times - if you've set Vh, Va, &Vs correctly, then the only thing that controls Ia is Vg. Always set Vg a bit higher than recommended before the Ia test - thus avoiding "whanging" of a tester's meter.Then reduce to the recommended value.
As well as recently testing a number of standardised valves, I've also been testing quite a few valves for local vintage chums. From the standpoint of 17 years into the 21st century, looking back at the vast variety of valves from 90/80/70 or whatever years ago - there is sometimes a helluva difference in manufacturer's specifications, compared to AVO's VDM, Taylor's Valve Charts, or Mullard's cards.
Regards, David
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