[etech]

I don't think many of us own calibration tubes, so your offer to lend a tube is appreciated.

What did those tubes measure on your 600A before you calibrated it?  The reason I ask is the TV-7 does not measure directly in GM so the readings have to be converted.  I'm not sure if I'd want to do more than a minor tweak on a 600A going on a converted TV-7 reading.

Hi John, Actually, from what I have read, a properly calibrated TV-7 is pretty accurate. They are calibrated at 125 micromhos per point. So, a calibration tube with a gm of 5000 micromhos, which is the Hickok charted average for a NOS 6L6, would read 40 on the TV-7.

I have a pretty good degree of confidence in my newly calibrated 600A. All of my 6L6 tubes read about 400 points higher, to the point of being abnormally high, before I re-calibrated the machine. Now, most of my tubes range from about 4300 to 5750, which to me puts them right where I would expect them. I have two lower rated 6L6G's which I know to be weak, which were in my 38-690, and they read 2800 and 3000 respectively. These two tubes also read in the questionable range on my Precision 10-54 emissions tube tester.

But to me, the most important thing is to have a tube which will be used as a calibration tube when I wish to read gm accurately on the 600A. As you probably know, any of these Hickoks (600, 600A, 800, 800A, etc.) with the English control with the dots on them which are used in setting the gm scale are known to be inaccurate. Frequently, the gm reading will vary 200 points or more, just by the direction you have approached the dot from. At least with some sort of calibration tube you can set the english/shunt control for the proper reading before you test your tube. Or, I could buy a better tester, lol!

Best regards,

Ed