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In Reply to: RE: tube testing question posted by Frihed89 on April 29, 2010 at 03:12:06
The MC tests should be a very reliable on a calibrated 539B. A particular tester may test a bit high or low compared to another tester, but the tests should all be internally consistent for his tester.
How do 12AU7 or 6SN7 types test? Do you see the same low-testing trends?
I have just recently tested a lot of 6DJ8 variants for a friend on my 752, and they did not test particularly test low or high for that matter. The 539B is at least as good a tester.
You may want to buy a bogey tube - a calibration tube with a known GM value to compare to his tester.
Follow Ups:
My uneducated view is that you want consistent readings from a tester for small signal tubes. Buy current production tubes from a reliable seller and use those as an example of what a new tube will test.
I suspect that whatever the standard of a "good" or "?" or reject indication was based up was related to a 6DJ8s use as a cascode VHF amplifier. How that is related to use in any audio circuit is anybody's guess?
I've got two 12AX7s, identical construction, both test as ? on my Hickok 533A. Both sound wonderful in the tone control of my Scott 222B and both sound great in my Dynaco FM-3 tuner; one in the MPX unit as an oscillator and inverted driver, the other as AF amplification.
For me, a tester is simply a signal device. The signal can be positive positives, false positive, positive negative, and negative negative.
For TV-Radio repair people the PP is an acceptable outcome; the NP means that if they think the tube is probably the cause of the problem, they try a new tube in the circuit; if it is a PN they sell a tube; if it is a NP, they sell a tube. The net result is that a tube checker may be super at picking winners only, and sell a lot of tubes. One repair guy said the tube tester was great for selling under warranty tubes.
If I want to try a small signal tube, I look for ones with ";ow" test results, especially when ? seem to work great.
best from Tucson
Bob
"He (R.M. Nixon) was a foul caricature of himself, a man with no soul, no inner convictions, with the integrity of a hyena, and the style of a poison toad." H. S. Thompson
I take issue, with respect, with your first sentence. In my experience with new prodcution tubes from China and Russia, it would be a mistake to use these tubes as examples of how a new tube should test. I have found that new out of the box tubes from these countries test very differently (usually lower) than their NOS breathren. Gain also seems to be different. Just my experience and there are other dealers out there with significantly more experience with new production tubes.
I agree to that. I would not even consider using a modern production tube as a guide.
Byrdshit
The ultimate test is in the gear and in your ears.
I also listen to not-so-hot-testing tubes and find they suit me well. I can't even count on one hand how many times I've pulled out a tube (good or bad test) because I felt it was under par and the sound reflected it.
Byrdshit
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