RCA 21" triage CTC20 CTC16x CTC12
 

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:sigh:, 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:D. 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:thmbsp:, 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.

Whatever your wife chooses.
:D

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.

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.

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.

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

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

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

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 :o

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

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).

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.

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,,. :D

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

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

Actually it was the cabinets that they had a surplus of. I worked on one that had a real fancy cabinet like the prior year CTC16X.
Curtis-Mathis had a cheapie knockoff of the CTC20, but used a 6KM6 horiz out instead. :thumbsdn:

R202 & R203, RCA is famous for burning those up in color sets, esp if there is leaky caps.

But the 2 470 ohm resistors in the vert yoke section really makes no sense, :o
the vert output transformer CAN'T put out that much power to be doing that, something must be really wrong :o
shorted yoke? horz- vert? You don't even need vert at this point, horz seems to be powered direct from +385v (3) , you could yank the vert output, (v9), disconnect the vert drive wires from the yoke, leaving the horz only, pop the top off the HV cage, and first see if you can draw a healthy arc off the top of the FBT, also at this point, if you measure any voltage at the vert yoke connect points, you know there is a problem.
And... if you CAN get a good healthy arc from the FBT and are feeling bold, unhook the CRT anode and close the cage and see if you can get any DC, stick it in a mason jar or something!
Yes, I have been watching a lot of shango66 videos!

Shango_66 gets right to the issue with great commentary. So far as I can tell, this TV was "run to fail" and later found when someone moved at last from a home that was also new in '66, and forever seemed new to the first ones to live there.

First the volume control froze, with the shaft worn out from a tool used to operate it. The escutcheon was all scratched up from this awful practice. Good thing the tuner knob and channel cup was OK, that tool would have annihilated a tuner shaft. The cord was arced on the plug/recept as well. Tubes as often the case after 50 years, were from all over, Radio Shack - Raytheon (Japanese) - GE - Sylvania - RCA (new logo) GE "engineering test samples" , an Amperex 6GH8A made in France O.o, but that "new" Colorbrite CRT had me going until I hooked up some tester-source DC to it and saw the purple genie of death in the guns.

After the CRT lost vacuum, even that did not stop someone from using it for sound. HV was hitting a brick wall, likely overloading the B+ via those resistors. No wax stalactites under the fly is very odd and I cant figure that out, being common for RCA. The HOT cap wire was scorched from the heat yet the 6LQ6 tested good:scratch2:.

I will get back at it this evening, and post some pictures of the schematic copy with bad parts circled. I have another yoke and will try that with the vertical wires disconnected. I have not measured 6LQ6 cathode current, that remains to give a clue. I will jig up the CTC16XL next. CTC12 is last and best hope for watching Rudlolf so Im going for speed, just like old days in a shop where you did easy stuff first to get it back in the customers home and get paid. Not always in that order:sigh:

Those "tough dog" customer sets similar to this CTC20 you had to take several breaks and clear your head to get at what the issue really is. When you nailed it finally, after a week of shake-down tactics, owner and everyone was interested in the play by play even the road guy.

I appreciate the help, thinking these were old hat for me. I must have forgot some basics of RCA sweep circuits.

I am really starting to wonder what the RCA engineers were smoking when they made the CTC-20...
From what I have seen, almost all leading up to it has had the FBT power taken from a shared point on the vert output transformer, and thus, if the yoke was not plugged in, HV was shut off as a safety feature. ( this is a guess by observation ).
But there seems to be no such thing in the 20, what were the thinking? :O

The mystery burned resistor in the cathode circuit of the regulator tube 6BK4 is R141 - 1000 ohm half watt. I replaced it with a 1 watt film resistor and like the 680 ohm 15 watt, does not run hot now. Not sure how R141 got burned in half. The tube is a good 6EL4A.

Well, if the dummies were running it with a bum CRT, who knows what kind of feedback it created, R141 is the path for the shunt regulator to try and clamp down the HV, if that let go, who knows what may have happened, especially if the HV rect let go, and flooded AC all over the place, it could have even got into the LV power supply, if they were really not watching things.

Here is the first of three RCA 21" color. The model is GH but the tag was half missing. The Sams lists possible models as GH608, GH618, GH626 or GH630, ending with a W for walnut finish. I have many extra knobs, least of the problems.

Attachment 201869

The 2.7 ohm resistor in the HV cup was a half watt and looked original, schematic and Sams picture shows it as 1 watt. It drifted to 4.2 ohms so the 3A3C was not bad as would have seemed. I replaced it with a 1 watt:scratch2:

That's a nice CTC20. Makes me miss my old one....If you get sick of it and it shows up at an ETF meet you could sell it to me fairly easily.

that looks almost exactly like my CTC-16XL :O

The one I saw in VoTech made an impression on me too, with the last-gen tube 2-PWB chassis no less. Two variations that look just like CTC16 AND CTC16x sets make a '20 necessary to round out any RCA collection.

If you have any tube-color (non-WID) by Motorola, its an even trade:thmbsp:

Until I take my last swing at it tonight, an update. The Fly is good and I got HV last night. The cathode current on 6LQ6 is 126ma. yet it was 195 initially. HV is low, 22 kV and control is at max. Boost at 1040v is right on.

The grid voltage on HV reg tube 6BK4 is affected by two 1.5 Meg 1-watt carbons, R139 & R140. These tested 1.44 and 1.55 meg respectively but the schematic note on both the RCA and Sams notes these as a "matched pair". This is a regulator problem because the only voltage out of whack is 6BK4-G1 which goes from 365 to 375 over the HV control range. Weak/worn 6LQ6's can cause low HV,, yet voltages on it are spot-on, even G3 which is not grounded but instead feeds some h-blanking network :scratch2::scratch2: Oh well whatever it takes to make it work, right?
Attachment 201876

The CTC20 apparently needed its own yoke, instead of the CTC12 yoke and convergence parts Im using on the jig for all those 15s and 16s I worked on for others. Even the jig is showing a full raster, all colors present and a blue H-K short in its gun seems to have healed itself:D. The HV cage and shields go back on so I can flip the chassis on its side to put signal and test using Sencore VA-48.

As much as we note RCA's shortcomings on design, shops all made good money because so many were sold and looked pretty darn good so everyone wanted them fixed at some point. Even RCA factory service had a shop to service all those C-M inspired service agreements.

True for the rectangular sets using a yoke plug. None of the 21" round sets used an interlock in the B+ as those did, all were connected with the familiar Red and Blu for Horz and for vertical, Yellow and Yellow with a Black-stripe all individual leads.

Sams did not show (dotted line) that the CTC20C has the Yel/Blk lead grounded! I lit the 6DW4 damper tube up when mis-wired the yoke leads initially:yikes:

Out of curiosity I have looked at almost all RCA CTC schematics, (sams), and noticed that almost all but the 20, power the horz from the vert output transformer, ( GRN tap ) , often from the far side of the centering pot, at first I thought this was a bit strange, cause it would feed vert pulses into the damper circuit and so on, then I realized they are using this as some sort of safety feature, and that most likely any pulses would get filtered out by the coils the have before the damper anyway, but what they are doing is, vertical centering (10 ohms) + vertical yoke winding (23 oms ish ) allows horz to energize, but remove it, and HV/ HORZ cuts out, to prevent screen burn.

Odd I thought they were all interchangeable.
But if you look closely at the Sams info, is says for the CTC-20, 70 degree, Horz 12mh Vert 38mh, same data for the 16/xl
but the 15 is Horz 12.4mh Vert 40mh, so I guess one from a 16 should work, but not a 15? I have no data about the CTC-12 :(

Im pretty sure yokes for 15 and 12 are the same. There are identical on the RCA schematics.

If you don't already have it, RCA vol. 1 Color TV service Manual (Tab Books #496)
https://picclick.com/Vintage-Tab-Boo...177180696.html
is a very important text if you want to understand all about these. .

Carl Babcoke never included a foreword like other Authors in this series BUT he must have really been listening in the service seminars RCA must have had. The troubleshooting steps for the ever-common issue of red-plate/No HV so common to RCA New Vista color TVs.

After the development of Color television it seems like some of the later models became victims of Corporate greed. I remember several chassis runs that had on going problems. They were good money makers for service, but didn't seem to hold up well to Zenith.

It's been fascinating to read the play-by-play on the CTC-20... the lovely Early American 1967 Zenith "Harvard" now alive and sitting in our living room was it's predecessor at Dave's!

I think the late 60s saw Zenith dealers proliferate for that reason, even here just 5 miles from Lancaster's New Holland Avenue CRT and orthicon plant.

Zeniths were more reliable, that's a fact. RCAs outperformed Zenith, that's a fact.

My recollection is that in our town, Zenith shops outnumbered RCA shops 8-1. We were only one of three that sold and serviced RCA. I remember the older shops just didn't like printed circuits and far preferred the hand wiring of the Zenith chassis. I suspect that was a big reason why there were more Zenith shops.

John

Why were TVs so hungry for 6GH8s? For that matter, why did every pentode/triode combo out there suck? I can't think of one that didn't have dome stupid issiue or another...

I think the manufacturers were trying to reduce tube count and except for GE compactrons, number of different tubes. The CTC16 had only two 6GH8A and it was more for convenience, combining 3.58 mhz osc and reactance, killer and killer and bandpass, a two in one tube.

Then...some wizard figured half a hard-driving 6GU7 could be replaced by half a 6GH8A and that led to higher demands on the pentode section. Maybe the relative success of the 5GH8/6GH8 in smaller screen sets led to mis-application in 25" models. :smoke:

Then as you say, 6BL8s in Motorola and Philco, 6KT8 in Zenith, 6GH8 in Magnavox, RCA etc. Seemed to fill tube caddys I collected over the years. I often read the 6U8 and 6EA8 were tougher of the triode-pentodes but the substitution is never guaranteed.

Spot on. The only way to be 99% sure the FBT is good or bad is
is to totally remove it & ring it. If it dont resonate its NFG. Shorted
turns were the most common fail on FBT's & yokes.

73 Zeno:smoke:
LFOD !

We used to buy 6GH8's by the gross every few months. The tubes just
seemed to suck BUT a lot of the problems were tube sockets.
Sets with 5GH8's were the 14" & 19" plastic cabinet sets. Same problem
with those BUT in the late chassii they got much better. Those sets ran
real hot & cooked up all the low level tubes. Add to that the low focus
CRT's & you have a real POS TV in a few years. That being said a good
one could throw a fantastic pix if you damn near retubed it gave
the CRT a clean & balance.
To add to the fustration if you "swap" GH8's the symptoms often changed.
You may start with no color, test the tubes then put them back
& get different symptoms. This drove the home tube tester types to drink.

enuf fer now
73 Zeno:smoke:
LFOD !

The RCA distributor sold a box of 100 Raytheon Japanese tubes for $98.00.
In the later model sets, the color osc tube was made by a different supplier. The only one, the other ones were RCA made.
I have an RCA CTC51K that has OEM 6GH8's that are Japanese. The horiz output as well.