• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Can I trust my Valve Tester

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I bought a huge box of new and used radio and television valves recently and have been putting them through my Taylor 45D Valve Tester.

As expected I got ano more than 10% recovery rate on the used tubes.

This was until I started to test the 26 6CM5 tubes. I tested cathode leakage, gm and anode current.
Of these I got:
6 tested 100% or better
6 tested 95%
6 tested 90%
1 tested 85%
2 tested 80%
2 mechanically damaged
2 with gm <80%
1 with marginal cathode leakage

That is 19 of the 26 tested what I would deem acceptable. 18 of them tested as good as the 4 NOS items I had on the shelf.

The problem with the Taylor 45D and possibly other Valve Testers is that on bigger power tubes they invariably test these at low voltages - in this case 100V Anode and Screen.

These tubes were all pulls from TV Horizontal Deflection Amplifier.
Should I assume:
1) There is something wrong with them that my Valve Tester is'nt revealling - should I retest cathode leakage at 250v Anode and Screen for instance.
2)They came from a particular TV repair man who replaced 6CM5s as a matter of course without bothering to check them.

Cheers,
Ian
 
Ex-Moderator
Joined 2003
I'm not familiar with the Taylor tester but I treat most valve testers with suspicion - including my AVO VCM163. Nevertheless, I'd say all of those valves look fine. It's time to reject a valve when heater/cathode insulation falls below 1M, and even then, it may not matter in some circuits. For example, poor heater/cathode insulation matters in the input valve of an RIAA stage but may not matter in a grid-biased output valve. I doubt if retesting with a higher anode voltage will make the slightest bit of difference.
 
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