Meck XB-702 restoration

[dtvmcdonald]

I had similar problems with my Pilot 3" set. It had hum bars in the picture, and would lose sync at the same phase of the 60 Hz.

It turned out to be mostly heater-cathode leakage and/or pickup from the filament line in either the tuner or IF amplifier stages.

Getting rid of it required buying three or more of each tube type, NOS, and trying tubes. If a new tube was even a little
better, I left it in and tried replacing other tubes. Repeat until every possible
change makes things worse.

It was worse at high signal levels. So:
Try a variable attenuator in the RF line (in the coax part of the line.)
Use an isolated transformer not a DC-connected balun to go from 75 to 300 ohms.
DIP-package counterfit Mini-Circuilts ones are available cheap in bulk from China and work fine.