RCA 621TS restoration -- in pictures

[DavGoodlin]

Nice work. I wonder if bumblebees can be split open, stuffed and re-glued. It would sure look good.

Did somebody mention not having a sams for the 621TS?
I found it in the Sams servicer vols 77+78

It shows that mind-bending LV power supply and cap voltages are not listed.

[charokeeroad]

Can't wait to see the final picture Tom. The underchassis looks Great !

[vts1134]

Originally Posted by Tom Albrecht

I don't think the Bumblebee was original, and those molded caps are not particularly amenable to restuffing.

For what it's worth there were no bumblebee caps in my 621.

[Tom Albrecht]

The next problem that needed attention was the broken pin on the socket of the 6AT6 first audio tube. Although there was nothing visibly wrong, a continuity check showed that the contact for pin 1 (control grid) was broken. With a little tug, it pulled right out, making the break very clear:



I thought I had an identical socket I could replace this one with, but checking my supplies, I did not. Even if I had had one, it was not entirely clear how I was going to get the old one out and the new one mounted without having the resort to screws to mount the new one.

I noticed that the original socket had two unused pins. By cutting a little bit of the bottom wafer away, I was able to slide out one of the unused pin contacts:





Getting the remnants of the broken contact out was much more challenging, but eventually I got it out. With a similar section of the bottom wafer cut away around pin 1 (already visible above), I was able to slide the good contact into that position:



Before trying to glue anything in place, I soldered the resistor and capacitor to the new pin, to avoid heating after gluing. Finally, after soldering, some 5 minute epoxy was added to keep the replacement pin in place permanently. This was done with a tube in the socket, so everything would be positioned properly. Final view:



With that fixed, I turned my attention to audio IF alignment. Since the 621TS is an early set that does not have intercarrier sound, alignment of the audio IF is critical. Basically every early set without intercarrier sound needs at least a little touch up of the audio IF alignment, both to get good sound quality, and to get the fine tuning to tune in both good picture and good audio at the same point.

This set was a breeze for audio IF alignment, and after just a few minutes, a perfect FM demodulator response curve could be obtained, centered exactly at 21.25 MHz. Here's the equipment I use for that -- the old HP analog sweep generator on top provides the sweep signal; the digital HP RF generator on the bottom is used for markers (it will only sweep up to 20 MHz, so it doesn't make a suitable sweep generator itself, but it will produce markers up to 40 MHz, which is fine), and the little Tek plug-in module scope in X-Y mode is used for the response display:



On this set, I don't think the video IF needs any touch up, since the picture looks good as is. Sharpness is good, and so is the low frequency response and DC restoration. So no need to mess with it.



Picture width is still a little narrow, so I will look into that further tomorrow, as well as checking all resistors for drifted ones to replace.

[charokeeroad]

I'm seeing fireworks on this end too Tom, Beautiful Picture, Great Work.

[tubesrule]

Riveting is not hard to do and rivets matching the originals are available and cheap. You do need some special tools for semi-tubular rivets which can be expensive, but sometimes you can find them cheap on ebay and such. I use a local place for supplies: http://www.rivetsinstock.com/

For doing rivets in the middle of a chassis where a hand or small bench squeezer is not practical, I just use a hand tool that holds one side of the squeezer set and back the other side up with a heavy piece of steel holding the other side squeezer and tap it with a hammer. Here are some that I've done using this method:

[kvflyer]

Originally Posted by tubesrule

Riveting is not hard to do and rivets matching the originals are available and cheap. You do need some special tools for semi-tubular rivets which can be expensive, but sometimes you can find them cheap on ebay and such. I use a local place for supplies: http://www.rivetsinstock.com/

For doing rivets in the middle of a chassis where a hand or small bench squeezer is not practical, I just use a hand tool that holds one side of the squeezer set and back the other side up with a heavy piece of steel holding the other side squeezer and tap it with a hammer. Here are some that I've done using this method:

That is exactly what I was talking about. I figured there would be some kind of supplier but didn't know what the rivets were called and where they could be obtained. Thanks for sharing the info!

[tubesrule]

Here's what a typical hand setting tool looks like:

http://www.hollanders.com/supplies/V...4-5cd139b88816

The setting tool or squeezer head must have the dimple in it for tubular rivets or they will just crush instead of rolling over as you set them.

You want to back the flat side of the rivet up with a concave tool so you don't flatten the head as you set it. Sometimes a piece of hardwood like oak can be used as it will give just enough to conform to the head without flattening it.

Darryl

[Tom Albrecht]

Darryl,

Thanks for passing along the info on do-it-yourself riveting. I think I'll get some of those supplies for future work. Screws always look a bit second rate in restorations when everything else on the chassis is riveted.

[tubesrule]

I also hated using screws where rivets were used originally as it just doesn't look good. Once you have the tools to do rivets, you'll find lots of uses for them. Terminals on coil, brackets, etc. I've got dozens of different size and type rivets that always come in handy. You may want to get some eyelets as well (those are the ones that are hollow all the way through and rolled on both ends) as you use the same tools for these.

BTW very nice job on the restoration so far!

Darryl

[ChrisW6ATV]

Really impressive work on that 621, Tom. I did not think you could outdo the job you did on your own set, but you may be getting there now.

I had a couple of terminals breaking out of similar sockets on my CT-100, but they were not themselves broken, and I was able to carefully reposition them and use small amounts of super glue to reinstall them.

[Tom Albrecht]

The last issue that needed attention was the lack of sufficient width in the raster. This is an unusual problem, since most sets I work on have too much overscan, and it takes some creativity to get the raster down to the correct size for the CRT mask. I think the manufacturers figured out pretty early that customers seldom complain about overscan, but will surely complain if the raster doesn't quite fill the screen. Perhaps the 621TS was engineered before manufacturers came to that conclusion.

No setting of the horizontal drive, linearity, and width controls would give me a big enough raster. Just a tiny bit too small -- not off by a mile. I checked all the components in the horizontal deflection system, and replaced some out of tolerance resistors, but there was no improvement.

What worked in the end was to change the tap on the big damper resistor in the HV cage. RCA specifically provided extra taps on this resistor for adjustment of horizontal linearity. I found that the lower resistnace tap reduced the size of the raster, and the high resistance tap increased the size of the raster. The linearity coil needs a little touch up after changing that tap, but overall, with proper adjustments, the high resistance tap gives a slightly larger raster.

This is the resistor in question:



After optimal adjustment, the overall raster linearity, both vertical and horizontal, is pretty good:



Not perfect, but pretty good for a tube TV. Many later models cannot do this well. The only ones that routinely beat this are DuMonts.

So we'll consider this set done.

[charokeeroad]

Tom, Can you give us a shot with the chassis in the cabinet. I realize the CRT doesn't quite have the support on the chassis that would make that easy but it would be nice to see it complete.

Really nice work Tom!

[dieseljeep]

I've been working on this stuff for 55+ years and I've never heard of that O'donnell brand of capacitor. They must've been replaced at one time in the life of this set.
The restoration really shows a great attention to detail.

[jmetal88]

Wow, that picture looks a lot better than the picture on the Zenith I'm working on looks right now! I still have a bunch of resistors left to check, though, I guess.