Question about the Pair of CT-100's at ETM Auction

[benman94]

This is the second time in 12 months that I know of that a 15GP22 has been falsely accused of being a dud. This is why anything I'm interested in gets tested with my modified Beltron. Always test a tube with a tester you're comfortable with and trust, to do otherwise could be an extremely expensive mistake.

[Electronic M]

Originally Posted by benman94

This is the second time in 12 months that I know of that a 15GP22 has been falsely accused of being a dud. This is why anything I'm interested in gets tested with my modified Beltron. Always test a tube with a tester you're comfortable with and trust, to do otherwise could be an extremely expensive mistake.

That, in a nutshell, is why I did not bid either of the 21" sets to my limit. I brought all the equipment I needed to vet all CRTs in the sets there, and the ~1-2 hours I had before the auction got eaten by swapmeet so I never had the chance to see for myself if the claims of good and bad CRTs were accurate. I've seen enough bad tubes called good and enough good tubes pronounced dead that I don't like to take others' word on things unless I'm letting go of a small enough sum, or getting enough out of the rest of the set to not care if the CRT is good. I've had several people get but hurt over my not taking their word on CRT condition, but if I'm shelling out a C-note or more and the rest of the set is not worth far enough over the purchase price to make up for a dead CRT then I feel it is only fair to allow the buyer to check the CRT for themselves first...And I'd encourage any buyers of my sets to do so if they feel the need.

[Electronic M]

The luminance deficiency was the most obvious culprit. The original white peaking coil on the contrast control above chassis had opened...I took the longest, but the most educational approach to finding it: comparing video at various points between my CT-100 and 21CT55 on a scope...I could have saved myself a half hour by following my hunch and putting a DMM on it, but the scope was more fun.

That got me a monochrome picture with all the contrast and brightness I could ask for...Turning up the color got me horizontal chroma stripes. Best yet color was actually synching periodically.


This is the only pic I got. I had it making a great picture on a different source when it would occasionally sync. Then I tried to adjust L43 (RCA part 78891) the reactance coil to make the sync permanent. It was sticky but came loose...Unfortunately, it was not the slug that came loose but the coil form and with it the wires that connected it to the terminals. leaving me with the osc. way off sync but still working. Once I realized what happened I removed the coil and tried to free the slug. Sadly the cardboard form was too brittle, and also ~1/8" of the very long slug chipped off...I managed to grab a similar form and rewind the wire, but it will not oscillate with my repair...I'm kind of up a creek presently.

Only thing I can think of is a CT-100 parts chassis....Or there is a very slim chance that coil may have been used in a 15" Dumont color monitor carcass I acquired recently. The Dumont is missing CRT/deflection hardware, flyback, and other things, but it seems to be CT-100 based. The Dumont's HV cage (what is left of it) appears to be exactly the same as that in a CT-100 as do the purity and field neutralizer coil connectors...If I'm lucky it uses the same reactance coil too...But then again I would like to make the Dumont work again someday and hacking it up for parts does not sit well with me.

After brief success, I'm back to monochrome again.

[dtvmcdonald]

Well, I'm now crying! That price for a good 15GP22!

You'll eventually get the oscillator to oscillate again. Coils at 3.58 MHz
can be rewound, you;ll eventually succeed. There are parts chassis around.

That color bar picture looks exactly like the one I first got on my set. Good
luck getting the red and magenta balancing well with the other colors.
Beware of AGC setting and color level on the modulator.

[EdKozk2]

Hi Tom,
I was thinking of any easy way for you to fix or replace your broken L43 coil. You could use an old 4.5mc sound coil. You would have to add some more capacitance in the tank circuit. Increase the 5pf to get a center frequency of 3.58Mhz. If you have an inductance meter, maybe you can measure your broken coil if it is still intact.
Ed

[Pete Deksnis]

Originally Posted by Electronic M

This is the only pic I got. I had it making a great picture on a different source when it would occasionally sync. Then I tried to adjust L43 (RCA part 78891) the reactance coil to make the sync permanent. It was sticky but came loose...Unfortunately, it was not the slug that came loose but the coil form and with it the wires that connected it to the terminals. leaving me with the osc. way off sync but still working. Once I realized what happened I removed the coil and tried to free the slug. Sadly the cardboard form was too brittle, and also ~1/8" of the very long slug chipped off...I managed to grab a similar form and rewind the wire, but it will not oscillate with my repair...I'm kind of up a creek presently.

After brief success, I'm back to monochrome again.

Check L42 for continuity. An open L42 is often the cause of 'loose' chroma sync in a CTC2 chassis.

Pete

[old_tv_nut]

Using a coil that resonates with a different size cap may work, but it's not the best idea because it will change the strength of the effect of the AFC circuit and therefore affect the stability of the pull-in as temperature changes, etc.

Better to get the right inductance and capacitance.

[bgadow]

FYI, RCA 78891=Meissner 17-6015. I did notice, while checking some Photofacts, that the 19CK1 uses the same part, and I suspect others do as well.

[Electronic M]

L42 was changed sometime in the previous owners' restoration(s).

L43 mesiner 17-6015 (thanks Bgadow for the cross-reference!) turns out to also be used in the Dumont monitor carcass I got at the ETF...Can't say I feel good about taking parts off of it, but others have done that enough in it's history that I'll need a parts chassis to get it working anyway...In picture form I pulled this coil from this chassis to fix the CT-100.


Color synch held for 30 min and only wavered on a VERY saturated scene.

[Chip Chester]

So as an aside, what is your picture source? As digital, then ATSC came onto the scene, the definition (or common practice) of 'legal' colors and black levels has changed a bit. And if you're converting from HDMI, HDR will really tax things. If you're using 'old' recordings (VHS/Beta) or a proc amp in conjunction with your modulator, or if it has one incorporated within, it may not be an issue.

[Electronic M]

I haf many sigi-nal sauces.

That is the main rack in my room. Bottom-up there is U-matic, LaserDisc, HDDVD, Bluray, DVD-recorder/VHS, DVR/DVD-recorder, 2 S-VHS-ET decks, CED/selectavision video disc player, SuperBetaHiFi, AV switchers, PC with S-video out, ATSC box, Blonder Tounge agile modulators configured to transmit, and hidden to the side a pair of mini cable boxes and a Roku. Before the ETF I tore apart and rebuilt/reconfigured all but the agile modulators on top to fix the flying spaghetti monster that it had devolved into through 3-5 years of not really properly reconfiguring it when needed but instead hacking on to the front accommodations for the switch to digital cable, the addition of HDMI for my HD-CRT Sony, and a bunch of other stuff.

Basement rack is a Blonder Tongue, VHS, Beta, CED, Cable box and a fairly literal bunch of video game consoles (also have LD and other crap waiting to be added to it when I get around to rearranging that cluster)...

Colorbar path consists of upstairs DVD transmitted, then tuned in by the VCR in the downstairs rack and retransmitted (the upstairs rack is hard to tune in the basement so this is the easiest workaround), then tuned in again by the VCR that feeds this video injection box https://antiqueradio.org/VideoAdapte...Television.htm

The TV program path was much simpler cable RF out from cable box (it only has RF for analog output) to the tuner on basement rack and onwards like the other path.

The CT-100 shall live in the basement close to my workbench until I am satisfied enough with its performance to make it a spot in one of my upstairs display rooms.

[Electronic M]

So with the covid lockdown keeping me in the basement I've been going after partially done early color projects....

Where to begin on this? Shortly after my last post Benman offered to trade his CBS 205 for my 21CT55... looking carefully I came to the conclusion that I'd be trading for the same chassis in a bigger less attractive cabinet with a smaller CRT and I'd be trading a set that needed an alignment and refinish for an unrestored chassis that might also need an alignment and decided to fix my 21CT55 (which has been working and looking excellent for a year and a half now and I should post that saga eventually).....one interesting thing on the 21CT55 was it didn't need an alignment...All it needed was the off tolerance IF resistors changed and the channel osc slugs retuned.

That led to me to pull nearly all the decent 6AN8s out of the CT-100 to replace all the weak shorted specimens in my 21CT55....the CT-100 sat dark since then with the tubes missing (and eventually a bag of swapmeet 6AN8s sitting on top)....
Late last week another slug cracked on my Moto 21CT2B so while I wait on another chroma bandpass coil from eBay for it I bounced over to the CT-100. After getting a fresh crop of 6AN8s in it replacing the 6DE6 somebody placed in the 2ND IF with the correct 6DC6, changing off tolerance resistors in the 2ND and 3RD IF, and changing the paper cap in the tone circuit the hack that recaped it left I was easily able to get it to pass decent chroma through the IF... there's some chroma/sound crosstalk in the lumina channel I need to fix yet (If resistor replacement in the IF I've since done hasn't fixed it) but it is now watchable.

I'm almost done going through the IF resistors. I also plan to replace the 1-2 remaining original leaking coils in it and the other peaking coils with the same ones I used in my 21CT55 (the ones miniman82 recommends from digikey). Whoever put in the somewhat random assortment of peaking coils in this set also did a lot of sloppy J-hooks (sometimes a J to another J to finally the cap lead) sloppy soldering and other baloney that makes me question their competence to select correct peaking coils. I plan to go through and change all off tolerance resistors in the color and video stages as well as the HV and to change the doorknob capacitors out before they can fail...
If progress holds I'll have this set done soon.

[WISCOJIM]

Good work, Tom.

.

[old_tv_nut]

Nice!

[etype2]

Very nice. You should turn off the lights and fill the VF with the image(s).