Testing Mullard 12AU7 on Hickok 600A

[ethanbriz]

Hi folks, I need a little help here. I found a sweet pair of "matching" Mullard 12AU7 square getter tubes at a garage sale today (and a host of others). Pulled out my Hickok 600A to test them, and Im a little worried.

The first triode on both came out at 3100 microhms. However, on an attempt to test the second triode, the needle doesnt budge for either.... not even a twitch. I had a very similar problem with another Mullard 12AU7 and 12AX7 I tested a few months back. Are these tubes bad, or is there something I dont know?

[kevinkr]

First step is to take a known good 12AX7A or 12AU7A and use your tester to blow it up, err I mean test it..

I am assuming that you know how to set up and use your tester properly. (Interpret tube setting tables, set proper filament voltage, set required bias voltage, set the switch for each pin correctly, test & read the correct meter range.)

First make sure the filaments in both triode sections are lit.

All joking aside find a known good "sacrificial" tube in the event the tester is killing them and test both sides. It is quite possible that there is a problem in one of the tester's switches that is causing it not to be able to test the second section. (This most likely - second most likely is an open filament in one section or the other.)

The fact that this has happened with multiple tubes makes me suspect the tester - hence the need to test it with a known good tube.