1949 RCA 9TC275 Restoration

[Penthode]

I have been spending my spare time over the last couple of weeks restoring a 9TC275. It uses the first RCA "large screen/ direct view CRT" chassis, the KCS29.

I bought it on Ebay a few months ago. The gentleman I bought it from cleared houses for a living. He told me it came from a better class neighborhood in the Lincolnwood/ Chicago area. It had been relegated to a damp basement for about 50 years and it showed.

I have rebuilt the cabinet base and shall soon refinish the cabinet. I had a go on the chassis in recent weeks.

I have restored seven or eight RCA pre 1951 chassis over the last 35 years. The paper capacitors are are nearly all leaky and bad. But the electrolytic capacitor seem to survive. I have replaced all the paper capacitors across a high B+ voltage even if they show no or even minor leakage, because they will eventually break down. I have left the paper if they show no leakage and have on a few volts across them (shunted by a low resistance). I found the resistor in series with the vertical hold control had gone high which made it impossible to obtain vertical sync.

The son and daughter of the original owners of the house from which this TV came, recalled it as children but the set was relegated to the basement in probably the late 50's. They did not recall the set being used after then. This may be true: certainly I could see there had been one capacitor change but all the tubes appeared to be original RCA. So it seems the set had not been on for a very long time

The electrolytics when disconnected and tested were very leaky and perhaps shorted. I always initially disconnect the electrolytic cans and see if they can be revitalized over a week by using a DC power supply to rebuild the dielectric. My Sprague capacitor bridge has a current limited hi-voltage power supply which is great for rebuilding the electrolytics. Each one came up and showed about 400uA or less at full rated voltage. I reconnected them after the rebuilding process and have bench tested the set on for about 24 hours and so far none of the electrolytics gets warm. I know that many of you on this forum like to change all of the capacitors in one go: I like to see how long they last. My RCA 8-T-243, which I have owned for many years, has all of its original electrolytics and it is fine.

This RCA set set uses the 50 degree deflection angle 16AP4 and is an incredible 22" deep. I have included some photos with the chassis set up on the bench: note the hi-voltage lead touching the rim of the CRT. Note also the off air signal is an HD program from PBS station WSIU in Carbondale IL. WSIU broadcasts AFD (Active Format Description) which switches the Zenith set top box between 16x9 and 4x3 automatically. Don't know what the benefit is to a roundie, but there you go.