In the end, tube testers are only something to guide you along the way. If your tester in fact has a "gassy" light, then you should keep this light in mind. I've tested tubes on such testers, however, only to find that the so-called gassy tubes function like any other. It all depends upon the circuit. Oscillator circuits, especially those in portable radios (battery), are the most sensitive to slight gas in the tube. Generally a tube will function quite well as an amplifier or output tube unless it glows purple (not blue!). When you see the purple glow, emission will go way down, and the tube may not even light properly for reasons I've explained before.

Actually, come to think of it, gas in a tube shouldn't make the needle go up to 1000. Gas allows current to flow in both directions--alternating current. With an emissions tester, the tube is the rectifier which supplies the meter with DC. If your tube is gassy and starts passing AC, the meter will actually read lower. I think that this is also the principal that the "gassy" light works upon--current flowing in the direction other than normal.

Anyway, in my experience, a gassy tube has never made the needle read higher, but actually made it read lower. As well as that, I have never had a tube not function properly that read 1000.

Thomas

:Most emission testers are calibrated to read 70 to 80 on a scale of 100 for a good tube. This should be in your tester manual. If a tube reads higher than this I would suspect it may be gassy or it may be an exceptional tube. Any tube that reads high is as suspect as a tube that reads low.
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:Dave