RCA 721TS restoration

[Zenith6S321]

I picked up an RCA 721TS from a local craigslist and restored the electronics. The guy I bought it from had got it from a used furniture store and refinished the cabinet in urethane, I think, but it has a bad scratch on top that I should do something about some day. Attached are some pictures. As the pictures show, I was very very lucky not to have broken the CRT while transporting the set, as the picture tube positioning feet were fully retracted and the CRT was partially supported by an IF transformer. This set uses the electromagnetic style ion trap. Someone added a cap across the width coil, to boost the width?, that is not shown on the RCA schematic. Dusty an complete, except for the missing channel selector, fine tuning knob and channel number plate. I later bought a channel selector and fine tuning knob, but I am still looking for a channel number plate. More pictures to follow.

[Zenith6S321]

The underside of the chassis looks very original, except for signs of the tuner having been removed before. And the ANT lettering on the lead-in terminal strip is upside down if it had been screwed to the cabinet, which it was not. The 1B3 HV rectifier was gassy, but most of the other tubes were in pretty good shape. I ran the 10BP4 CRT on the CR-70 at 8V for a few hours. It then tested at the very low end of thee good emissions band and the cutoff only worked with the next higher bias voltage than specd. Two of the electrolytics were leaking, one badly. I restuffed the electrolytic cans and most voltages were close, but the HV was 6KV instead of the specd 8.5KV. With only the electrolytics and 1B3, it did show a raster . I cleaned the chassis and hooked a DVD player RF signal on channel 3 and got the first image. Lots of problems that I hoped recapping and out-of-spec resistors would fix. But, all the sections of the set worked and even got vertical and horizontal sync!

[M3-SRT8]

Yes, some of the 721s had a cap across the width coil. My 721TS doesn't have it, but my 721TCS does.

Not a bad job on the cabinet. You can get decals for the slat front controls.

Here's my restored 721TS and TCS:

[Zenith6S321]

I replaced all of the paper caps and the mica caps in the deflection curcuits. About half of the resistors were over 30% off value and were replaced. The fine tuning control stop had broken off (a little tab on the shaft), so I soldered a piece of copper to the shaft and it works well as a stop. The buckshot parts replacement got a weak picture. I then used the CR-70 to do one rejuvenation, which increased the emission nicely, but the cutoff stayed weak. But the TV liked it as shown in the last image.

[Zenith6S321]

Those two beautiful sets you have M3-SRT8. Great looking cabinets and screen images. I think my set has its original CRT, which does not look as good as yours, but is watchable.

[Penthode]

Aren't the early RCA sets just great? You have a nice one there.

Funny, I have found most of the early RCA 1B3/8016 HV rectifiers go gassy.

[Zenith6S321]

After performing the RCA alignments the cross-hatch pattern shows pretty good linearity. The sound was just barely detectable. I performed the sound IF alignment which improved the loudness. I also found that I had to clean the tuner contacts with rubbing alcohol. I then added a capacitor between the vertical yoke to the CRT grid to reduce the retrace lines.

[Zenith6S321]

I agree Penthode, these sets perform amazingly well considering the technology of their time. I am also impressed with the circuit design, considering all the parts that drift off value over the long years, but yet the sets still function pretty well.

[Zenith6S321]

Here is one last shot of the set in my living room sitting under my wall that I use to project my "TV" onto. The 721TS is showing the same image as the projector. A lot of the "HD" shows are still 4:3 aspect ratio, as you can see by the round earth on the 721 .

[Phil Nelson]

That's a great looking picture. I restored the electronics on my 721TCS some weeks ago. Still waiting for the cabinet to be refinished. Can't wait to put it all together!

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[M3-SRT8]

Originally Posted by Zenith6S321

Those two beautiful sets you have M3-SRT8. Great looking cabinets and screen images. I think my set has its original CRT, which does not look as good as yours, but is watchable.

Yes, thanks. I had to spend more time on their cosmetic restoration than electronics, but I usually do that on all my restos. I like 'em both, and the TCS is a favorite.

You possess very good TV troubleshooting skills. Better than me.

I think Jake LaMotta is having trouble with his 721. We better help him out...

[Adam]

Originally Posted by Zenith6S321

I replaced all of the paper caps and the mica caps in the deflection circuits....

I usually don't just go replace any mica caps like I do with all the paper ones when I restore a set. But just 2 months ago, I went to watch my 721TS, and couldn't get horiz sync. (The oscillator was running at the wrong frequency, it wasn't a problem where the picture wouldn't lock into place). It turned out to be a leaky mica cap. While I had it apart, I replaced all the micas that had anything to do with the horiz osc, but left the others. I wonder if bad mica caps are becoming a common problem in these sets?

[Zenith6S321]

Thanks to all for the kind comments. I was preparing to start restoring my 21CT55 when I found the ETF web site and the videokarma forums and realized my sets rarity. The ETF and these forums contain a wealth of helpful information, wonderful technical discussions of early TV technology and circuit design, investigations of historic sets, and restoration advice that I doubt could be found anywhere else. And Bandersen's youtube videos are wonderful. Once I learned of the possibility of acquiring early post-war sets I decided to restore one or two of those before attempting the 21CT55. Next is an RCA 630TS. Its cabinet is unrestored with a scratched finish and some venier starting to crack on the curved top. I was wondering if, like with antique furniture, it is best to preserve the original finish if possible, or to stip off the old finish and attempt to replicate it? Refinishing wood is new to me, so I will probably take the least destructive path for now.

[Zenith6S321]

Adam, I replaced the micas just in case any decided to go bad after so many years. I had read Phil's 721TCS restoration web page and followed his advice. My digital meter verified the old micas values were within tolerance, but I do not have a high voltage leakage detector. So I decided to error on the side of caution and replace all of them in the H and V circuits where they might damage hard to find parts.

[kvflyer]

A very nice set and great job. I am envious! I am even more envious of the 630TS. I remember dad having one in the basement and his comments that it has "30 tubes!". I think the 630 draws almost as much current as a 50s color set!