Rca 721tcs

[N2IXK]

Ok. Got the ratty speaker and lamp harnesses fixed. The wire was just too brittle to withstand the handling it will surely get during the restoration process, so I just replaced them with new wire, spliced to the ends from the chassis which haven't been flexed and are still sound. Have some black nylon expandable mesh sleeving that will cover the colorful new wire.

After this, I decided to bring up the B+ very slowly. I decided to leave the field coil/filter choke disconnected, so I was only energizing the 2 caps right off the 5U4 tube. Solid state 5U4 plugged into socket so it will start conducting at low voltages. Milliammeter connected at speaker connector B+ interlock pins, to monitor leakage current in the caps. Voltmeter connected across caps (betwen the +280V bus and the -85V bus). Plug set into variac and watch cap current. Bring variac up until meter shows ~5 mA leakage. Voltmeter says ~20V across cap. Leakage drops pretty quickly to <1 mA, when I bump the variac up again to show 5 mA again. Voltage now ~40 V and leakage drops off again.

Lather, rinse, repeat.

Eventually got it up to full working voltage (365V), with about 0.8 mA of leakage after 30 minutes at full voltage. Caps staying nice and cool, and ripple looks pretty low. Cut off the power, and caps hold charge like they should.

Swap in a 5U4, and do a "hard start" from wherever the variac was resting (~90V), and it comes right up, but somewhat lower voltage because of the tube rectifier. Goose up the variac to get about ~380V to simulate a bit of overvoltage or cold start , and everything looks great. Leakage < 1 mA after 30 more minutes idling.

Next up...connect the field coil and hope that the other caps come back as well as these 2 did. That's probably tomorrow evening's adventure...