RCA 21" triage CTC20 CTC16x CTC12

[DavGoodlin]

I have three complete RCA "new vista" 21" color TVs, none work and all three had bad CRTs when I got them. I need to get ONE of these working so I can enjoy some classic cartoons and movies for the holidays.

After that Zenith 21" went to a new home, the living room is empty and
I miss clearing RCA's multiple hurdles, which are a given! So, which will it be?

The latest arrival is a plain walnut-screw legs CTC 20C from upstate NY. So far it has a gassed CRT (Sylvania re-gunned) and flyback that won't ring test but looks clean, along with several fried resistors and frozen power switch/volume control. Pretty hopeless, or is it?

Almost a year ago, I ventured 2 hours south to Delaware for a beautiful Danish walnut Karlstat GG721W using a CTC16XL chassis. The Colorama CRT label gave false hope - the green gun had no emission because its heater element was GONE. However it had a replacement fly. I cant wait to put this chassis on the jig to see what other gremlins exist. This may be the "easy" one.

Long ago, a locally-placed CL ad for a free tv was pointed out to me by Kamakiri himself. I arrived to find a complete Lynnhaven CTC12 213G612MU in Mahogany with a Colorama CRT replaced 1967 but a typically skanky flyback. The CRT has a H-K short in blue gun - just needed the isolation trans inserted and now its my jig tube. Thanks to another Tim at VK, I have an NOS FLY 273. The other work needed is typical of RCA's 4-board flat chassis, but likely more than wrong with it than the 16x.

[reeferman]

Whatever your wife chooses.

[Electronic M]

Originally Posted by reeferman

Whatever your wife chooses.

Depends on your cabinet and chassis preferences the cabinet face masks on the 16 and 20 almost certainly swap so you could mix and match.

Sounds like the 16 chassis is best but all should be fixable. The 20 chassis has the 6GH8 law of guaranteed bad tubes going against it...A lot of stuff can cause a fly not to ring from rectifier filaments loading it to shorted caps... I'd assume %75 chance the fly is okay till deeper digging is done.

[Yamamaya42]

Personally, I'd hit the CTC-20 first! I have always wanted to play with one of those! 6GH8As from hell!!
You don't know for sure right now that the FBT is bad, it may be, then you are in a really bad spot, cause it seems to be ultra unobtanium,
I would just replace any fried parts, and see if it can get HV without smoking anything, if it can, you are in luck, if not, move on, you only risk a few resistors and perhaps a HOT.

[DavGoodlin]

The fun is to compare these three versions of RCA color. I suspect the CTC12 will be the spouse's preference though. It is sort of Early American like the cherry hutch, etc.

I have only seen one CTC20 before. It does have (7) 6GH8s, four of them tested bad. Yes, I wanted to do it first and I did replace bad resistors but no HV and the VA-48 tells me the HOT is bad though it measure 600 ohms.. If I'm lucky, an NOS fly-back may be available.

[JohnCT]

My opinion is to not waste your time on the CTC20. Those toilets had a lousy picture and terrible color when they were new (I was there).

The 12 and 16 will both give you a superior picture, as good as you'll ever see on any vacuum tube TV.

John

[JohnCT]

Originally Posted by DavGoodlin

....the VA-48 tells me the HOT is bad though it measure 600 ohms..

The resistance between the plate cap of the horiz out and the HV rectifier is the first quick test when checking the fly, but if it passes that test, there's still the possibility of a shorted turn. An ohmeter treats coils like resistors and a single shorted turn renders a coil useless and won't be discernible with an ohmeter. The VA48 will ferret out those with shorted turns.

John

[Yamamaya42]

Originally Posted by DavGoodlin

The fun is to compare these three versions of RCA color. I suspect the CTC12 will be the spouse's preference though. It is sort of Early American like the cherry hutch, etc.

I have only seen one CTC20 before. It does have (7) 6GH8s, four of them tested bad. Yes, I wanted to do it first and I did replace bad resistors but no HV and the VA-48 tells me the HOT is bad though it measure 600 ohms.. If I'm lucky, an NOS fly-back may be available.

which resistors were bad? ( via Sams #s? )

[Yamamaya42]

Originally Posted by JohnCT

The resistance between the plate cap of the horiz out and the HV rectifier is the first quick test when checking the fly, but if it passes that test, there's still the possibility of a shorted turn. An ohmeter treats coils like resistors and a single shorted turn renders a coil useless and won't be discernible with an ohmeter. The VA48 will ferret out those with shorted turns.

John

I'm not gonna fall into that trap again!

my FADA HOT had the primary of much less than the 180 ohms than all the schematics said it should have, by almost 1/2, but it's still working fine, VERY confused by that one

[JohnCT]

Originally Posted by Yamamaya42

I'm not gonna fall into that trap again!

my FADA HOT had the primary of much less than the 180 ohms than all the schematics said it should have, by almost 1/2, but it's still working fine, VERY confused by that one

We all know it's not uncommon to have a bad value in a schematic, but it's very uncommon to have more than one schematic make the same exact error.

My best guess is that FADA made a running change to the fly after the schematic was printed or that other companies redrew the original factory schematic in their own notation and transferred the incorrect reading at the same time. I know that early SAMS credits the original manufacturer in helping. I wonder if early SAMS were simply redrawn and later ones were drawn with a working example.

Speaking of running changes, I have an Andrea I was screwing around with earlier this year and it has a tube and associated circuitry that the SAMS doesn't show.

John

[old_coot88]

The CTC-20 was a low-end special. We sold a few, and they were dogs right out of the box. First run had weak vert sync, and the factory issued a field mod requiring changing two resistors in the sync separator circuit. The chassis was a mashup of the CTC-19 (designed for the new 19" rectangular tube), back-engineered to drive a 21" round tube. It's as if the factory was overstocked with round tubes and needed a quick way to use 'em up. And it was the perennial 6GH8 hog (as was the '19 and all its later derivitives).

[dieseljeep]

Originally Posted by DavGoodlin

The fun is to compare these three versions of RCA color. I suspect the CTC12 will be the spouse's preference though. It is sort of Early American like the cherry hutch, etc.

I have only seen one CTC20 before. It does have (7) 6GH8s, four of them tested bad. Yes, I wanted to do it first and I did replace bad resistors but no HV and the VA-48 tells me the HOT is bad though it measure 600 ohms.. If I'm lucky, an NOS fly-back may be available.

The last CTC20 I repaired and sold had a bad flyback and the CRT had a H-K short on one of the guns. The RCA distributor didn't have a flyback in stock and had to order it. That was when the set was seven years old!
I used an isolator and replaced the flyback and sold it reasonable.

[Yamamaya42]

Originally Posted by JohnCT

We all know it's not uncommon to have a bad value in a schematic, but it's very uncommon to have more than one schematic make the same exact error.

My best guess is that FADA made a running change to the fly after the schematic was printed or that other companies redrew the original factory schematic in their own notation and transferred the incorrect reading at the same time. I know that early SAMS credits the original manufacturer in helping. I wonder if early SAMS were simply redrawn and later ones were drawn with a working example.

Speaking of running changes, I have an Andrea I was screwing around with earlier this year and it has a tube and associated circuitry that the SAMS doesn't show.

John

https://i.imgur.com/x1izfje.jpg

I never DID work it out.
EVERYTHING matched...
every capacitor, resistor, tube and voltage, EVEN the part # was the same on the FADA part list, and it shows 180 ohms pin 1-2 and 240 2-3
I did get 240, but not the 180. was very confused, the same is shown on EVERY fada clone and rca 630ts and one like it.
no idea why my FBT is weird.
and just to be safe, I got a new replacement RAM FBT that was listed as a replacement for this FADA, in case this one blows, but so far,,.

[DavGoodlin]

0: CTC20-I checked the fly again after unplugging 2AV2 and 6JE6 disconnecting the hor yoke, damper and boost terminals. The VA-48 ring test showed in the good zone on 1-2 settings. I think Moyer's has a flyback but trouble shooting is not done.

Oddly, while powered up with good HOT voltages (G1 drive and G2 screen) and making no HV this morning, the two 470 ohm resistors in the vert yoke bypass started smoking. That smell now takes me back only 10 years, when we still heated with coal -LOL.

I was already trying to make sense of the initially toasted resistors; 680 ohm/15 watt , 560 ohm 7 watt , 1000 ohm 6BK4 grid.

Ill post some pictures with schematic, etc

[DavGoodlin]

Originally Posted by old_coot88

The CTC-20 was a low-end special. We sold a few, and they were dogs right out of the box. First run had weak vert sync, and the factory issued a field mod requiring changing two resistors in the sync separator circuit. The chassis was a mashup of the CTC-19 (designed for the new 19" rectangular tube), back-engineered to drive a 21" round tube. It's as if the factory was overstocked with round tubes and needed a quick way to use 'em up. And it was the perennial 6GH8 hog (as was the '19 and all its later derivitives).

Very interesting that RCA did what Philco and Magnavox did. Reverse engineer the new rectangular chassis for a surplus of round tubes.