1949 RCA 8TR29 restoration

[Radiotronman]

I've decided not next project will be this rca 10" rca tv/radio combo table set. I've restored the 8TK29, which is the console version , before so I'm familiar with the chassis. I also have a spare chassis if anything is bad in it. Hopefully this doesn't have a bad tv/radio/phono function switch it it like the console did. This is an extremely heavy set, but I like the looks of it. It has the early rca design that requires you to pull the front panel off to pull the crt out, as it is not strapped to the chassis. I'll start the usual cleaning and parts list. This also has the cool two way viewing dial for the radio.

[Radiotronman]

I've got around to recapping this set and finally got the horizontal semi stable. Now I'm trying to figure out why my video is so washed out and the focus control doesn't change it much. I also have no actual sound, other than buzzing too. The am/fm radio doesn't come on either, no doubt a result of a problematic function switch in these sets. I ran into this on the console like it I restored and had to bypass it.

[EdKozk2]

The focus looks ok to me. Your scan lines look focused. The video signal looks smeared and weak.

[decojoe67]

I always liked that RCA model. It's uncommon and almost looks pre-war, especially with the radio dial.
Lately I've noticed that many of the controls on my sets, both radios and TV's, are really becoming touchy. Much more so than years back. These sets are 70-80 years old now and I guess it should be expected.
Good luck with the restoration.

[old_coot88]

Originally Posted by EdKozk2

The focus looks ok to me. Your scan lines look focused. The video signal looks smeared and weak.

I would first check continuity of all peaking coils in the video chain downstream of the vid.detector.

[Radiotronman]

Ok I'll start looking there...thanks!

[retrogear]

I agree your scan is in focus. To me it appears to be a video IF amp stage faulty. Looking at the Sam's 88-9 there are 4 6AG5's V4-V7 video IF amps. Since you have buzz in the audio, audio IF signal is taken after the 2nd stage V5 so the fault would be in V4 or V5, either a bad tube or measure the plate voltage on pin 5 of those tubes should be approx. 100VDC. If that is missing, could be an open IF coil. It is normal to get buzz in the audio when a video IF amp is faulty. I did tube television service for many years in the last century Larry G

[old_coot88]

Originally Posted by Radiotronman

Ok I'll start looking there...thanks!

Do you have a source of raw video that you could inject right after the vid.detector? That would determine if the fault lies downstream or upstream of the v.detector. When localizing this kind of problem, think of the vid.detector as the "continental divide".

Granted, at first glance it looks like something in the IF strip is severely out of whack. But the same visual effect can be caused by an open peaking coil or even a resistor 'downstream' in the video chain.

[Electronic M]

That era of RCA is known for leaky IF stage mica caps...I'd check those.

[retrogear]

Yes a method of video injection would be ideal. In my introduction, I mentioned a lot of test equipment got auctioned off when our shop closed in 2000. We had a B&K Video Analyst which could inject IF or video signal. It had a kinescope tube inside with changeable video pattern mylar sheets including the classic Indian Head pattern. Damn I wish I still had that !!

[Radiotronman]

Thanks for the tips guys. I checked continuity with the peaking coils and didn't find any open. I checked all of those 6AG5 tubes already and all tested good. I'll check those mica caps and check resistors around those tubes next.

[Electronic M]

Originally Posted by retrogear

Yes a method of video injection would be ideal. In my introduction, I mentioned a lot of test equipment got auctioned off when our shop closed in 2000. We had a B&K Video Analyst which could inject IF or video signal. It had a kinescope tube inside with changeable video pattern mylar sheets including the classic Indian Head pattern. Damn I wish I still had that !!

I had a 1076, and keep a 1077...IMO any collector planning to do more than 5 restos should have one. They can localize so many troubles in so many circuits they are worth the time they save.

[Radiotronman]

I have a BK 1075,1076 and 1077, but haven't used them much. I probably need to pull the 1077 out and learn how to use it on this set. I haven't used my capacitor tester much either, but I will try using it in the mica caps.