To me getting a tube tester is easy, but learning how they work is fun and educational. Do you care? The manual for the B&K just has a note and says of the 12AX7, 'Tube good if it reads 22 or more'. ![]() The problem with my tube tester and the B&K 747, is it always test tubes like a 12AX7 as low, due to lack a variable test signal (as most testers don't have either). They are excellent (dynamic) testers and similar to the B&K 707 (tube version of the B&K 747), They share basically similar circuits. I have a dynamic tester, a Mercury 1000, similar to the Mercury 1200. It will do most of what you need, thumbs up or down on a tube. Do you have to have a dynamic mutual conductance tester? An emission tester can be had for under $100. There are many good testers, brands and models. Are they that much better? Not for me, I just want to check for shorts, gas and how relatively strong it is. For the ones that are truly desirable, Hickok and Triplett, the prices have got silly, into the +$1000 range. Here is a secret, tube testers share much of the same circuitry. For later radios and guitar amps or stereo amps it is fine. If you are working on old radios with 4 pin tubes, no this will not work. Tone Lizard list this with many other units and their attributes, pros and cons. ![]() ![]() The last three B&K 747 sold for over $300 to $350 + shipping lately on eBay, good luck.
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