• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

300B Board Layout question

@6A3sUMMER - THAT was fun, entertaining and educational. Seriously.

Results in order: far-near, turned OPT 90 degrees, close in and farther.

Got my answer. But I’ll play with the PT too (taping ALL non-connected wires) to be sure. Orientation of the PT core seems to be the same, but what the heck, I got time.

Thank you.
 

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You can also do the same thing with a pair of wired earbuds. I use an adaptor from the 3.5mm jack to some alligator test clips. Hook those to the OPT (or whatever you want to test) fire up a small filament transformer/choke/whatever and play with the orientation of both the source and the OPT. Clearly can hear the results.