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.

[robert1]

Damn, that's got a good picture on it. :-)

at least it shows that the crt is in great shape, electronically.

[Penthode]

Originally Posted by robert1

Damn, that's got a good picture on it. :-)

at least it shows that the crt is in great shape, electronically.

I feel I have been lucky with the CRT. When I bought the set, I knew it was the original 1949 tube and expected it to be a dud. It had a brightener on it, which wasn't a good sign.

I tested it with my B&K Tester and there was absolutely no emission. Zilch! With nothing to lose, I tried rejuvenation. One blast and then measured emission was nearly 100%. No sign of gas, it seems to work okay without the brightener.

It is a little dim but is watchable: Let's see how long it lasts.

[Eric H]

Very nice picture.

I have a large console with that tube and chassis and it also has a great picture. (my avatar is from that set)

I wonder how much has to do with the Metal/Glass tubes having "precision" face plates, no distortion to speak of compared to molded glass tubes.
I suppose it being a higher end set they probably put a bit more effort into it also, higher 2nd anode voltage etc.

[Glenz75]

What an incredible picture on that! Its amazing how CRT's can be bought back from the dead and produce an image like yours. Great stuff.

[Penthode]

I have been bench testing the chassis for over a week. The electrolytics are holding but a few resistors had drifted and were replaced. Namely the first audio plate resistor hs gone high (resulting in distorted audio) and the positive end resistor of the horizontal hold control had drifted upward from 150kohm to over 300kohm. This made the synchroguide alignment difficult. IF aligment is still to be done.

I have had a go on the cabinet. It was pretty bad at the bottom with water damage. The veneer had split and the front legs fell off. This required a lot of glueing, clamping and wood replacement around the feet. I am in the midst of stripping the old finish. The large doors covering the screen have a faux marquetry that was printed on. Pretty cheap for such an expensive set ($469 as advertized in the September issue of "Life"). I found I can flatten the surface with fine wet and dry and I shall try applying a layer if varnish and then flatten until smooth. The marquetry painted surface is not too bad.

Here are some pictures to date.