Help the Museum get its Display Sets Working Again

[etype2]

Mike jigged a 21FBP22 CRT to my Westinghouse H840CK15 chassis during restoration. This was to test circuits and verify the restored chassis operation prior to installation of the 15GP22 to help avoid possible mishaps. A few photos of the Westy performance on the 21FBP22. The images are a bit blurry because the voltage values are from a chassis designed for the 15GP22.

[Videotechie]

I hope this post motivates someone to save 15" to21" test jigs...

[Penthode]

It looks like the tube connection to the jig 21fbp22 is minus dynamic convergence only?

[Electronic M]

Originally Posted by Penthode

It looks like the tube connection to the jig 21fbp22 is minus dynamic convergence only?

It would have to be since 15GP22 designed chassis lack the correct sweep transformer windings to drive electromagnetic convergence, but at the same time because the electrostatic convergence element of a 15G draws virtually no current the chassis doesn't need a load on it's convergence output wire.

Given a chassis designed to drive a 15G can drive a 21FBP22 sans dynamic convergence, a late 70s early 80s test jig with an inline CRT (which doesn't need electronic dynamic convergence) that has the yoke impedance matching box to allow it to work with a 21FBP22 chassis, should work on a 15GP22 chassis. At that point it becomes a matter of mounting the test jig CRT in the cabinet convincingly and replicating the 15GP22 internal mask so the swap doesn't jump out at you as badly. The difference in phosphor dot shape, pitch, and primary colors will be noticable to someone who has seen a real set as will the curvature of the phosphor dot plate, but if the faux outer glass and inner mask of the 15G are replicated well enough it might take a while to notice with the set off.

I have a good set to try this on while waiting for a 15G to materialize. I have a 19" rectangular delta gun jig I could use as a crude proof of concept (already used it to sub for 21" round sets). If I could get a 13-15" inline jig that would be ideal.

[Videotechie]

It's awesome to see everyone's talent at doing jigs and displays. I'm glad I posted, wasn't expecting such a great result of restorations showing a way around a 15gp22. Thought I would mention just in case finding a set with bad CRT. Is the museum successful on rebuilding these yet.

[Pio1980]

Originally Posted by Electronic M

If you're working with a 21" Zenith roundy change all the Sprague Bumble Bees, the white ceramic shell paper caps (I think they might be Elmenco brand), the black plastic electrolytics, and arguably the the can lytics. Adjust the horizontal efficiency coil for minimum horizontal output cathode current.
One performance mod I like is to replace the tube focus rectifier with a modern 5KV PIV 200nS recovery part from Mouser...The focus adjustment peak looks sharper, and focus is more consistently good with it.

There was talk of the 15GP22 potentially being replaceable with a 14" large neck rectangular tube found in the first Japanese rectangular color sets. The deflection angle was close enough to probably work, custom mounting would be necessary, dynamic convergence would be extremely hard to achieve if possible, but the biggest thing stopping this is that those Japanese sets are collectible and significantly rarer than CT-100s.


The RCA 21CT55 was basically a CT-100 with the sweep and convergence circuits factory redesigned to drive a 21" color CRT. I've got working examples of both. The 21CT55 uses R-Y/Q demodulation instead of I/Q demodulation...The only difference is one demodulator transformer and 1 resistor. I acquired a spare CT-100 I/Q transformer and plan to convert my 21CT55 eventually.

I've seen someone who blew up the flyback in their 21CT55 and replaced it with one from a CTC-20 roundy color...If someone was REALLY motivated it might be possible to take a CT-100 look at the 21CT55 sweep/convergence differences and try to implement them with say a CTC-17 rectangular set's sweep circuits and use that to drive a 15NP22...It would be a Frankenset at that point.

I've also seen 13-15" rectangular service test jig CRTs with yoke impedance matching boxes(to make them compatible with everything from 60s roundys to 90s BPC). It could be possible to impedance match a 15" inline gun rectangular CRTs yoke to the stock sweep of a CT-100. If done correctly you wouldn't need dynamic convergence or chassis mods, just new CRT mounting. Seeing as other members have run 60s roundy CRTs off 15GP22 sets for test jig reasons this mod should be possible to implement.

If my 15G ever craps out I may try some of these ideas.

I Remember seeing one of those Japanese rectangular oddities on the bench at the Ft Jackson Army post electronix craft shop I frequented in the 1970s, I think Hitachi or Toshiba for Sears.
I was going to ask about that set in a posting.

[dtvmcdonald]

The need to work on those sets is probably just as dire this year as last.
We need to contact McVoy and see what's going to go on in that regard.
I'm available to contine work on the CTC5 or alternatively on a 21CT55.

The CTC5 needs a full alignment as an absolute minimum. I'd need help to get
the chassis to the bench and preferably a spare yoke since horizontal drive is needed to get the color system working right.

[Philco123]

I'll give you a hand on the CTC-5 alignment, Doug. We've chatted over the years at previous conventions. You may not know me, but I think you will remember me when you see me at the convention. Jeff

[reeferman]

In the Zenith vertical section there are two items that look like 3 legged disc capacitors. One is called a vertical integrator (Zenith 87-4), the other vertical feedback (Zenith 87-5). They are found in all Zenith roundies. Each has its own color dot. The one that causes the most trouble (I've forgotten which one) causes the picture to pull up from the bottom.
I always replaced both of them.

If you have a plastic cloverleaf (the thing that holds the convergence coils) be on the lookout for a replacement. I always replaced it.

[rld-tv01]

Along with what Videotechie implied: is it possible for the CT-100 chassis to supply a composite video signal with some added custom circuit? There are 15 inch CRT computer monitors with composite video input. I have a 15" Mitsubishi multisync monitor with various inputs including composite.

[Electronic M]

Originally Posted by rld-tv01

Along with what Videotechie implied: is it possible for the CT-100 chassis to supply a composite video signal with some added custom circuit? There are 15 inch CRT computer monitors with composite video input. I have a 15" Mitsubishi multisync monitor with various inputs including composite.

There's a 1954 circuit for injecting composite video into a CT-100/21CT55 to use as a broadcast monitor. Others have improved on it by doubling the capacitance of the lytics and figuring out how to make it a plug-in/clip on device...I followed all that when I built mine.

Others have (the dead CRT crowd) have picked off the RGB CRT drive from the set along with H and V sync and used that to drive VGA monitors before.
Personally I rather try to make a test jig with a 15" rectangular inline CRT work as a reversible modification and see sweep circuit performance instead of using the CT-100 as a glorified tuner.

[dtvmcdonald]

Originally Posted by rld-tv01

Along with what Videotechie implied: is it possible for the CT-100 chassis to supply a composite video signal with some added custom circuit? There are 15 inch CRT computer monitors with composite video input. I have a 15" Mitsubishi multisync monitor with various inputs including composite.

Well, yes but ... most computers take RGB. Its very very easy to make a circuit to convert the 15GP22 gird feed leads in a CT-100 to standard
solid state RGB levels. I posted the circuit ... it just three FETs, three
bipolar transistors to drive 50 Ohms, and resistors. The only problem
at all is that it needs three 2-10 or so pF trimmers to get the frequency
response right, and a wall-wart to drive. Results are excellent.