Advice sought for 1968 RCA GL-644W

[holmesuser01]

A KINE is short for Kinescope... another word for the PICTURE TUBE. It's pronounced almost like the name Kenny. a kenny-scope.

You may have a tube called a 6GU7 that is the G-Y / Blanker tube. Check its socket as the blanker can cause the screen to go white. Check your schematic on the HV cage. I may be wrong about the type, but look and see which tube is your blanker.

[Chad Hauris]

The 6GU7 will be used in the deluxe type RCA's such as a CTC-25 or CTC-30.
The cheaper models such as the CTC-31 or 38 will use I think a 6GH8 in this function.

[Radiophile2001]

The schematic will mention which tube is the blanker tube?
Yep, there are 6GH8s--5 of them. I have the back on it now and it's against a wall, but if I can determine which is the blanker tube, I will focus efforts there. Indeed, it went to a white screen, and then it went black finally.
I'm really trying to avoid pulling the chassis just yet. May be an easy fix here.

thanks

[Radiophile2001]

Update on the RCA:

* Re-soldered five of the connections between the chassis and PC circuits. They were broken connections before, from what I could see.
* Found that one of the two tubes I did not replace with new ones has gone out. That may explain why the CRT went black.
* This tube also should have been a 6CL3 from the diagram, but is a
"6CJ3/6DW4B/6CH3". Any advice on this? It was lighting up when I first got the set and when the set was working. I can't get it to light up...cleaned the tube plug and checked for breaks in the solder....Wiggled the tube a bit too. The tube has a shaking sound inside.
The blanker tube seems OK to me, but I have no tester. It's a new tube (NIB).
The Chassis is CTC38A.

Thanks!!

[jstout66]

Investing in a tube tester would be a good thing Your damper tube shouldn't be making a rattle noise when you shake it. The type that is in there is fine. I think that's the "newer" type that RCA used and I'm surprised a CTC-38 didn't have that type in there from new. You have a good set, but they have the higest flyback failure rate of any RCA chassis I am familiar with.

[Radiophile2001]

Quick question:

What is a flyback failure and what are the symptoms of it happening? ;-)
So when I go to get a a new damper tube, which number would you recommend?

Thanks

[Chad Hauris]

Flyback failure occurs with an overload on the horizontal output circuit causing the flyback (horizontal output transformer) to burn out. I had a CTC-31 flyback meltdown, it started smoking and burned everything in the HV cage. I have been installing fuses in the horizontal output cathode circuit, 300 ma (1/3 amp) seems to do.
You will want to make sure the horizontal output current is not too high...for this I have removed the cathode fuse I installed and replaced it with a 6.3 volt lamp, then adjusted efficiency coil for minimum lamp brightness.

The weird thing is that the series filament portable RCA tube color sets had horiz output protection built in but the consoles do not. One type used a dual circuit breaker with two terminals for the power line and two for the horiz output cathode. Either a power supply overload or horizontal output overload tripped the breaker.
Another type used a thermal fuse in the HO cathode circuit. This sensed temperature near the HO tube and if the tube got too hot it would open the cathode circuit.

[Radiophile2001]

Chad (or anyone);

I never smelled anything burning or smoking on the set. But it seems when I put the last two tubes in (which included the 12HG7), it got pretty bright, like a new set. I also adjusted the back of chassis to maximize brightness, sharpness and picture quality. After that, it seems things started to go downhill.
However, I don't think the HO transformer was burnt out because for two days there before it died I was able to get it working again by either positioning the 12HG7 tube just right, or lifting up one side of the set and setting it back down "hard."
Is it possible that all of the adjusting I did and all the new tubes overloaded something?
Note the 6CL3, aka, "6CJ3/6DW4B/6CH3" died on me in the process. Will be checking eBay today.
PS. I still have not pulled the chassis. Working through the bottom of the set (cut away all the particle board that had air wents and removed) with the set face down.

Thanks again for your help and advice,
Carl

[bgadow]

A possibility: perhaps dropping the set actually broke the glass on the damper tube? I recently repaired a portable color set with several cracked tubes; when they were replaced the set worked fine. I also recall that the H.O. tube on my CTC-5 cracked when I moved it (gently) from one end of the house to the other. Does the tube look foggy white inside? Look for a crack around the base. Try a new tube in there and see what happens. You shouldn't have trouble finding one-pretty common. I would buy it from www.radiodaze.com but there are plenty of good sources.

[Radiophile2001]

Hey, Bryan,

The tube has no fog in it. It has an uneven dark stripe around the base, but it's smooth. Not sure if completely smooth glass could have a crack in it or not, but sure hope so in this case.

I got a damper tube NIB on ebay for $2.00. It should be here tomorrow or Thurs. Will update.

Thanks, Carl

[Radiophile2001]

Update #3:

Indeed, the new 6CL3 damper tube works and has lit up the screen, but nothing more. Just a white, lit up, blank screen with no audio.

Ironically, when I pull the 12HG7 video output tube out completely (the genesis of the problems in my opinion), nothing changes. Same white screen, no audio, except for the usual low frequency hum at full volume. The tube V/O lights up though when plugged in. When I wiggle it, I can hear static on the speakers and I see one of the pins (through the glass of the tube) sometimes display a small electric spark for a short time.

I've also noticed when I touch the chassis, this low frequency humming sound diminishes to some degree.

The video output tube plug plastic is cracked and pieces have chipped off. The bottom contacts for it have been re-soldered, but I think I need to replace the plug. No idea where to get one though and not sure I am good enough to replace the plug without causing more damage! ;-)

Thanks for helping solve my little puzzle here!
Carl

[Adam]

Just a white, lit up, blank screen with no audio.

First, I'd check to be sure the IF amp. tubes are good, and that they're connected in the socket, I think a bad or not lit up IF tube would cause that. As for the vid out tube socket, I've never had to change a tube socket on a circuit board before, but I'm sure someone here has. On one of my sets that uses circuit boards, some previous repair man had soldered a new socket ontop of the old one, to avoid damaging the board further, it doesn't look pretty, but it seems to work ok.

[Chad Hauris]

On CTC-38's the IF stages are transistorized. I have seen a power supply problem knock out the 80 volt supply to the transistors and thus cause no video or audio. The last time I fixed the problem there was a bad wire wound resistor in the power supply near the filter caps.

On that tube socket repair I have done like Adam said just used a regular chassis mount socket. I busted up the old socket and used a desoldering wick to remove the old contacts. Then I soldered long bare wire to each pin on the new socket, put the wires through the holes, solder at the board then run the bare wire back the PC board trace to the next connection point and solder there too.

[Adam]

"On CTC-38's the IF stages are transistorized."

oops, sorry for the confusion, I've just seen a few sets lately with that same problem caused by bad IF tubes, so I had that on my mind.

[Radiophile2001]

Thanks. Would the V/O tube's having no effect on the white screen/no sound issue whether it is plugged in or not likely mean something is not right with its socket/socket connections (the tube is OK), or perhaps be more about the IF stage transistors being cooked?

I'd really like to try and repair the socket, but not sure if there's an easy way to do it. It's not in that bad of shape yet. If I pop the socket out, can I ask what I should look for to see if it is in working order?

I just don't understand how the tube could light up, but have no effect on the problem, plugged in or not....

Perhaps I need to find and solder more ground connections between the PC boards and chassis?