Restoration Commences on 1947 RCA Victor 721TCS

[Penthode]

Finished off another 8 hours running DVDs on the 721TS now reaching 43 hours since reforming the original electrolytic capacitors. I am impressed with the performance of this set with only 21 tubes. Lots of audio volume, no buzz likely because of its full split sound design. The video is sharp but the resolution above 3MHz is missing since the design has only three IF stages. The lack of any AGC is not a problem with no analog over the air available. Would have been curious how it would have been necessary to adjust the contrast control when switching between local and fringe stations.

I recall using my RCA 8T243 (kcs28 chassis) for analog over the air. This is the set I have kept the longest, having been given it in 1970. (It incidentally still runs on its ordinal elwctrolytics). The high class RCA design for 1948-49 sets feature full 4 MHz resolution, a more sophisticated sync separator and RCA's first television AGC solution using peak sync detection. But most impressive were the dual adjacent channel traps. Despite the wider bandwidth, the adjacent channel rejection was so good, you were able to receive deep fringe signals immediately adjacent to strong local stations. The 721TS had no adjacent channel traps. No problem with a modulator now feeding the set.

But the RCA sets in the late forties were built like tanks. Later design sets, especially with larger screens and with larger deflection angle CRTs put a stress on all of the components which would result in reduced reliability.

So tomorrow we should hopefully be able to reach 50 hours on the original 73 year old electrolytic capacitors.

[Kevin Kuehn]

Originally Posted by Penthode

But the RCA sets in the late forties were built like tanks. Later design sets, especially with larger screens and with larger deflection angle CRTs put a stress on all of the components which would result in reduced reliability.

What are your thoughts on the air core high voltage transformer that RCA started using around 1950? I'm assuming it had something to do with the new wider deflection CRT's, although other manufactures seemed to be using something like a ferrite core flyback transformer with good success. It appears that they used that air core on everything from a 12" to 19" CRT.