JohnC

Another newbie who found this forum while researching tube testers. For the difference in transconductance, you seem to be focused only on the difference in plate voltage. Running 0 volt bias at any plate voltage, the curves are sharper, hence marginally less transconductance than with bias. Plus 0 volt bias will exceed the allowed plate dissipation at nearly every plate voltage. I got into this because after I retired (former military radar tech), I started restoring '50s and '60s era shortwave radios. I really wanted a TV-7, but I haven't been lucky enough to find one at a price I want to pay. I picked up a WW II era I-177B. It will test vintage tubes (don't care), most 7 pin miniature receiving pentodes that I am likely to come across, and do an acceptable job testing 9 pin dual triodes (12AX7 and 12AU7) with homemade adapters. For me for now, that is . . . good enough. Dec. 18: In the last month I have picked up up a couple of Hickok 600As for repair and restoration. One will be for me. If I don't need the other for parts, I will calibrate it and sell it.