Help the Museum get its Display Sets Working Again

[Steve McVoy]

Help the Museum get its Display Sets Working Again

Hello Everyone!

With the unprecedented crisis of covid 19 hopefully in our rear view mirror, we are looking ahead to our 2022 Convention.

There is one thing however that needs be addressed. The reality of museum’s working TV set exhibits is a little stark. Because of consistent visitor traffic, coupled with a lack of conventions and member participation, many of the sets have stopped working.

Over these last several years we have lost several members that were instrumental in helping us maintain our exhibit sets, we also had postponed the previous 2 conventions in response to ongoing public health crisis. This didn’t help.

We have several black and white as well as a few early color that need some service.

Because of all of these factors we are this year soliciting all members, new and old, who have the technical expertise, to come help us get sets going the morning of the convention.

The museum is fully equipped with tools, tubes, parts, and test equipment.

Work on the sets will begin at 9 AM on Friday, May 6, the day the Convention starts. I will be there with donuts to supervise. Please help us get the museum sets working again for our visitors!

Blake Hinkle, Volunteer Coordinator

Register for the 2022 Convention
https://earlytelevision.org/2022_convention.html

[KentTeffeteller]

Steve,

If I was near, I'd be there helping you folks. Hope you get some volunteers.

[Yamamaya42]

Originally Posted by KentTeffeteller

Steve,

If I was near, I'd be there helping you folks. Hope you get some volunteers.

same for me, 1300 miles is quite far for me.

quite out of my range.

even Kilgore, Texas is 4 hours away from here :O

[AlanInSitges]

Bob Andersen mentioned he's going this year and will be doing some presentations. I suppose they could just chain him to a bench and make him fix things, like Breaking Bad but not.

[Electronic M]

I may try going early Friday morning to be there early in the afternoon... It'll depend on my work situation then. If I get hired some places won't let you take a PTO day in the first 3 months (in which case I sneak out at 2-4PM and hit the road then).

[bandersen]

That's my plan. Leave early on Friday and help out when I get there. Should be about a 6 hour drive - maybe less.

[zenithfan1]

If all goes well, I'll be there too and am willing to lend a hand.

[dtvmcdonald]

I intend to arrive in time to work Thursday and Saturday, assuming there
will be somebody else there Thursday to help with removing and carrying chassis. I intend to worn on either the 21CT55 or the CTC5 (Deluxe) or
with a miracle, both.

[TV Engineer]

I'll be there Friday morning to lend a technical hand.

[bluenorm]

i witch i could be there to record everything fpr prosperity.

[Videotechie]

I had an old color rounded zenith that worked for a while since it was a zenith. Is there a way to make some old sets more reliable to avoid common failures even if have to engineer a solution? How's the crt rebuild going? Not preferred but can CRT substitutes be done as backup supplies for rare color tvs and prewar b/w sets.?

I KNOW I'm gonna hear it, CAN a generic color CRT substitute for the CT100 be done just to make an otherwise non functional set operational? I think the challenge in the future is just to keep sets working. Is there any TV museum displays showing a video of rare sets working, with only limited turn on events. Just a few thoughts to keep old sets relevant.
It seems the parts and labor to repair these historical pieces is just getting harder to find.

Those CT100 CRT's are complicated- pretty much experimental and developmental with that combo of glass and metal external envelope. What about some vintage test jig color crts or old arcade color crts, can they be used?

A true hack, but ct100's will be able to run for next 100 years. Is anyone saving surplus color and b/w crts before they hit the scrap heap?

HAS ANYONE TRIED RIGGING SUCH A REMEDY on a CT100 to make it work???? Can anyone suggest substitute CRT's for a CT100.
Kinda a large piece just to display.

[old_tv_nut]

21 inch round color tubes were all electrically and physically interchangeable, as a rule. The major differences were in the phosphor composition improvements over the years.

The 15GP22 is a unique item both physically and electrically, using electrostatic instead of magnetic convergence, for example. The CT-100 chassis will not drive any later tube.

The choices are a working 15GP22, or a CT-100 cabinet with guts removed and replaced by a flat panel display, hardly a restoration.

[dtvmcdonald]

The CT-100 will drive any 21" roundie as far as signals goes. It can easily be modified
to provide focus. The bigger tubes need a higher high voltage. That would have to be
provided by an external HV supply., which you can buy on ebay. I would be afraid of
trying to get a higher HV using a tripler from the horizontal output tube plate.

The big big problem is convergence. It would be a major problem to connect up a
roundie convergence board to it, but surely doable.

What I did before I got a new good 15GP22 for my CT-100 was hook it up
to a modern (~2000) Sony high grade pro monitor of the same size picture,
just sitting on top of the CT-100. This is essentially trivial ... its done with a
5x5 inch of perfboard with six garden type transistors, resistors, and three
trimmer caps, running off a wall-wart. It takes the three color signals from
the CT-100 directly from the CRT grid lead attachment pins and reduces
them to standard voltage 50 ohm lines. The green
provides sync.

The picture on the Sony is identical to that on the 15GP22 except for the much
finer stripe pitch and the fact that its rectangular.

This same circuit would of course drive an LCD flat display inside the cabinet.

I just unplugged the HV and focus and regulator tubes, leaving the rest of the
sweep operational. That's needed to keep the various internal sync loops working.
If I unplugged the DC restorer tube it made no difference, because the monitor redoes that.

[old_tv_nut]

All true and good, if what you want is to view the result of the CT100 signal chain. And I want to add that what you did was great - I would have experimented the same way, given the opportunity.

I took the OP's desire to be a CT100 chassis with an approprately sized CRT running in the CT100 cabinet.

[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.