Stupid question about CRT swaps??

[freakaftr8]

Not that I would ever do this but has anyone ever swapped out a round CRT with a rectangular CRT? Are there differences in voltages? My friend has an RCA, probably a ctc-39 and he has no chassis in this unit, but the donor ctc-16 I have with no CRT, the chassis is good, could he put that ctc-16 chassis into his ctc-39?

[jpdylon]

The deflection angles are different and you would need to modify the convergence circuitry for the rectangular tube.

[Bill R]

You would also need the pincushion correction circuit.

Bill R

[bgadow]

I think the CTC-17 was a rectangular version of the CTC-16. You could compare the schematics for some idea. I wouldn't be surprised if you have to swap flybacks to get it to work right. If you have the time, I can't think of a reason not to try it. Fun to experiment!

[kx250rider]

Heck of a lot of work, but true; all the CRT voltages are the same. The biggest problem would be the yoke and deflection circuitry.

Charles

[freakaftr8]

Thats cool, what years were the ctc-16 chassis in produstion for?

[jpdylon]

64-65 IIRC for the 16 chassis

[kx250rider]

Through '66 too, for the 16XL. Then there was one more roundie that RCA made to get rid of the last round tubes in about '68 or 9... I think it was a CTC-30? It looked exactly like the smaller CTC-38 and had a solid state audio output if I recall.

The 12 came in '62, then there was the 15. Not sure what years those and the early 16 may have overlapped.

Charles

[Chad Hauris]

The later chassis round set was a CTC-20. I have one but have not got around to working on it yet...it actually has a CTC-31 chassis minus the pincushion components rather than a CTC-38 chassis. According to my book the CTC-20 was produced in 1967 or 68. The CRT faceplate and controls look exactly like the most common type of CTC-16 set.

The flyback circuit and vertical output transformer circuit are slightly different among the two to accomodate the pincusion components in the CTC-31 chassis but the rest is the same.

I put a flyback from a Hoffman CTC-17 rectangular clone set into a Silvertone CTC-15 clone round set one time and it did work but the width was a little low. All of the flyback connections were the same as I remember.

[TV Engineer]

when I was in High School, I was given a Magnavox 21" round color theatre with a U45 chassis in it. I liked the set, and of course the stereo, but I didn't like that "big, old fashioned" round screen staring at me in my bedroom (it was a low end theatre, and did not have doors on it.) Besides, the corners were cut off on a round CRT, and I wanted to see the whole picture.

I worked at a Magnavox service center, so there were lots of old sets around that were scrapped, and the chassis and other usable parts thrown into the cellar for future use.

I had a 23VAQP22 CRT that had been salvaged from and Admiral color set, and I wondered if I could adapt this tube to my Mag theatre. The answer was yes, and it was actually easy.

From the cellar of the shop, I scared up a mask for a set that used a 25AP22 with all of the hardware and the shield, a yoke, and a convergence board. These probably came from a set that used the U904 or U911 chassis, as they were the first 2 that Magnavox made that used the rectangular CRT. Since Magnavox was pretty consistant with hardware patterns, the new mask replaced the old without having to drill a single hole. I rewired the yoke to match the 4 wire configuration of the old 21" round yoke, and using a schematic from each chassis, was able to match the wiring to the convergence board 1 for 1. Then, of course, I replaced the CRT socket.

The results were amazing.

The set performed as if it were designed to use the 23" CRT, with absolutely no convergence, width, or pincushion problems whatsoever. I realize that most of this was dumb luck now.

I would NEVER do it again. I've learned to like that "old fashioned" CRT staring at me!

[TVtommy]

FWIW, I did a CTC-31 fly into a CTC-20 roundie (bad fly) and aside from ringinging out out a couple of the terminals, it was nearly a 1-for-1 swap! I also found width a little on the low side but the raster does fill the mask (just barely). You have to be looking hard to notice it (usually when the a/c compressor kicks in). Thats pretty neat about the Maggie mod, reminds me of some of those early Radio-Television mag. articles about "upgrading" your "oldfasioned" round screen b&w set to one of the "modern" rectangular crt's just introduced to the public. Some xfmr suppliers even marketed complete kits along with mask and safety glass and templates! must have been a good idea at the time, especially compared to the cost of a new set when you already had a decent operating one, albeit one with a small round screen Oh well, we all know about hindsight and that 20-20 thing

[Big Dave]

The closest I ever came was running one of my roundies on the Telematic. It looked bad, as in vertical issues as well as convergence, but it helped me diagnose other issues.

I had heard from a (possibly retired) repairman several years ago, that the manufacturers offered a kit to convert a round color to rectangular. Can someone confirm this? Motorola's 19 to 21 conversion kit doesn't count here.

[fujifrontier]

what about rectangular to roundie?

[Keefla]

Originally Posted by fujifrontier

what about rectangular to roundie?

I wonder how a cheap chinese chassis would look running a 15gp!?

[fujifrontier]

:devil:

experiemnt time