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the more I am persuaded an emissions/short only tube tester has significant limitations for predicting tube performance.
So what _can_ I reliably claim to prospective buyers about the two dozen+ used/NOS EL-509s I have stockpiled for the past 20 years after testing them with a B&K 607 (or other emissions tester if the goofball that sold me the 607 ever delivers it)?
Since I am preparing to sell my Transcendent Sound T8-LN OTL (just too hot in sin city to use it much) I figure to include the tube stockpile in the amp sale, and want to include only "good" tubes that are safe and effective to use in th amp in the future for replacements.
transconductance tube testers. Hope someone in sin city can help you with a transconductance tester.
An emissions tester is not a reliable indicator of a tube's condition. Get a transconductance tester that is rugged and will hold its value, like a TV7DU. Small, accurate, simple to use and holds value.
a TV-7/U for $10 at an estate sale and had it calibrated. They now sell for $250+.
I purchased a TV-7/BU for $100 in Taiwan and had it totally refurbished , calibrated, and modified by Dan Nelson for $500. This would now cost $900+.
However, I did find some other transconductance testers on eBay for $300.
A complete test of power tubes needs to include measurements under actual operating conditions. For me, testing and matching is a two step process. First, I test and match the tubes for transconductance using a Hickok tester. Then I install the tubes in an operating amplifier and match them for cathode current.
The Maximatcher can test and match power tubes in a single go, but it's fairly expensive (and currently out of stock). In your situation, a transconductance test is sufficient. Many sellers on the big auction site use this approach. I would include one set of matched spares with the sale, then sell the remainder separately.
You are correct, the simple tube testers can only detect a short, and the emission of the device.
For Power tube matching, transconductance at a given plate voltage is far more meaningful (gain for triodes in a driver / preamp setting is what is needed, along with noise)...
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