Restoration Commences on 1947 RCA Victor 721TCS

[Penthode]

It is up to 45 hours now. I investigated the picture width problem. I just performed routine voltage measurement and found the horizontal oscillator plate voltage a little low. The 120kohm plate dropping resistor had drifted upward to 150kohm. I replaced it with another 120 kohm 1 watt carbon composition resistor (originality of course) and the width was restored.

I saw the width control adjustment was screwed all the way in to maximum before the set was allegedly retired to the attic 60 years ago. So this must have been an old fault.

I have reverted testing with an older expiring 10BP4 to continue waiting for the anticipated expiry of the electrolytics. I want no more hours than necessary on the CRT.

Somehow I don't think there is going to be a failure. The electrolytics are running cool. And this hasn't been luck or good fortune: my two other pre-1950 RCA tv's have all their original electrolytics and run fine. It is running now and has done another 10 hours continuous running today.

The key is patience reforming the capacitors. That is leaving them attached to a light trickle current 24 hours and slowly reaching the rated maximum voltage. If you do not hurry the process, the capacitors should survive. And I am only speaking for RCA sets: I cannot speak for other manufacturer's sets designed to a budget.

Will aim for 55 hours running time tomorrow.