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Old 10-08-2015, 11:57 PM
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RCA CTC...Something? poor HV output.

I'm not sure which CTC chassis it has. Originally I wanted an RCA to begin with, and I ended up with one today. I'm selling both of my Zenith's to Jim.

It's a New Vista set, Model GF 631, if someone knows which CTC this is, that would be awesome!

The high voltage is very poor. If the probe I have is accurate at all, the set is only producing around 12kV. It does display a picture, even though the voltage is poor. Adjusting the HV Output only changes it 1kV or 2KV, not much adjustment.

I don't hear any arcing in the flyback box, and there is some melted wax, but no carbon tracking so the flyback isn't arcing out. I don't have any spare tubes for this kind of set. I'd like to know where to start before I have to suffer the pain of ordering them all on ebay.

It worked fine about a year ago, and it's just been sitting since. I have all the pictures of it. I'll post them below.


The pictures below show it was working a year ago and how it looked, a year ago.


Last edited by Arcanine; 10-09-2015 at 02:07 AM.
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Old 10-09-2015, 12:04 AM
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I'd have kept a Zenith and dumped the RCA.....Tubes+PCBs=more frequent harder to fix troubles....As some one who runs an RCA(clone roundy) and Zenith(hybrid rect) side by side as daily watchers and has done so for 5+ years I can tell you that the RCA construction method/circuits are more of a pain to fix (and need to be more often) when they act up.

Depending on the chassis variant I probably have most or all of the tubes in my stocks. If it is a CTC-15 set I could probably sub known good tubes from one of my sets to test it.

If you have not tried the HV reg adjustment, then you should....If that don't help, pull the top cap off the HV reg tube (may need to place in a jar to prevent arcing) and see if the HV improves....If it does the reg needs work....If not suspect the HV rectifier on back to the H osc.
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Last edited by Electronic M; 10-09-2015 at 12:11 AM.
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Old 10-09-2015, 12:07 AM
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You have a CTC16 there. Any previous service information/parts replacement? If not then it's probably full of stock components.

Some might suggest a resounding "full recap!" I think that the capacitors in the RCAs of this era are actually quite reliable, but unless you're able to solve the low HV issue by swapping out the Horizontal Output, Damper, HV Regulator and Rectifier tubes then you're going to have to get a print and start checking voltages.
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Old 10-09-2015, 12:20 AM
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Quote:
Originally Posted by StellarTV View Post
You have a CTC16 there. Any previous service information/parts replacement? If not then it's probably full of stock components.

Some might suggest a resounding "full recap!" I think that the capacitors in the RCAs of this era are actually quite reliable, but unless you're able to solve the low HV issue by swapping out the Horizontal Output, Damper, HV Regulator and Rectifier tubes then you're going to have to get a print and start checking voltages.
No idea. I was told the CRT is much newer, and it looks it by how it was working. It's an RCA "Hi-Lite", it has a few GE Compactrons throughout the set, all the HV tubes are still RCA lables, thus I presume original. I can get a stable, blurry picture out of it, so the horizontal output is working.

I have 4 Dentron 6LQ6 tubes that are still strong, the HF amplifier they lived in was still doing good strong power when I used it. I swapped one in, and the HV won't even kick in on these. It has an RCA 6LQ6 in it as is, and it's working fine.
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Old 10-09-2015, 12:31 AM
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That is bizarre. A weak Horizontal Output can cause HV issues, but you'll usually get a picture that won't fill out horizontally. I think it's safe to say your stock HO tube is doing it's job, but those other tubes you have should light up and run too.

And that CRT looks amazing too. You got a good one!

Are you running at full brightness? Will the picture "bloom" (defocus and expand) when the brightness control is fully advanced?
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Old 10-09-2015, 12:37 AM
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I can see NO WAY....you ONLY have 12KV here. The pix is WAY too good--and full. 12 KV would NOT give a full raster--and focus woulod likely be VERY bad..


YOU DEFINITELY need to check your HV PROBE !! I'll BET...from that pix...you are getting at LEAST 23KV.
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Old 10-09-2015, 01:06 AM
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Quote:
Originally Posted by rca2000 View Post
I can see NO WAY....you ONLY have 12KV here. The pix is WAY too good--and full. 12 KV would NOT give a full raster--and focus woulod likely be VERY bad..


YOU DEFINITELY need to check your HV PROBE !! I'll BET...from that pix...you are getting at LEAST 23KV.
I'm sorry. I did not mean to incite confusion.

The pictures posted first are of the set before the previous owner stored it. It does NOT display like this today. That is how it was. and should be...



That is what I see on it, today. After about 15 minutes of on time, focus goes, then the picture fades out.
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Old 10-09-2015, 02:18 AM
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Take a look at the two 6GU7s on the far right end of the chroma board. Are their heaters lighting?

If not, with those heaters cold, here's what's happening: the plates go 'waay positive and drive the (G1) grids of the CRT positive (since the plates are direct-coupled to the CRT grids). The CRT beam current goes into avalanche, producing exactly the symptoms you describe. And this overcurrent is extremely hard on the 3A3, flyback, and H.output tube.
Don't run the set in that condition.

Of course if the 6GU7 heaters are lighting, then the problem lies elsewhere.

If the heaters are cold, it's caused by a broken ground in one of the two ground stakes on the far right end of the chroma board. So re-flow those grounds. This problem was endemic to the CTC-12, 15, 16, 17, and 25.
Even if the 6GU7s are lighting, re-flow those grounds anyway as a matter of routine.
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Old 10-09-2015, 11:21 AM
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I have the same set (ct16) and in my case the first symptom was the lost of converging adjustments in one of the color(green) hv was check and was detected at 17 thousand top, a few days later was at 15 and the poof. chassis was removed and all the voltages coming out of electrolytic tested ok. the high voltage transformer burned. it was replaced with a nos and all problems were solved.
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Old 10-09-2015, 11:37 AM
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what old coot88 describes happen to a friend of my ct15's or 16, exactly as he stated. he discovered by pressing down the 6gu7 and later pressing the board near the ground stakes thus making ground. an easy fix.
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Old 10-09-2015, 12:39 PM
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To add to Old Coots' post: there are two brown wires that run on TOP of the PCB between the 6GU7s and the 6GY6s. These carry filament voltage to 6GU7/6GY6 on right side, and due to heat, corrode to green dust where they enter the PCB hole.
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Old 10-09-2015, 01:11 PM
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Quote:
Originally Posted by DavGoodlin View Post
To add to Old Coots' post: there are two brown wires that run on TOP of the PCB between the 6GU7s and the 6GY6s. These carry filament voltage to 6GU7/6GY6 on right side, and due to heat, corrode to green dust where they enter the PCB hole.
Both of my 6GU7's heaters light up, and it appears the aforementioned connection has seen a reflow already. I tried wiggling them around a little, and nothing changes at all.

I also noticed there is a fair amount of arcing out of the top of plastic cup on top of the fly back box. The wire to anode goes in though there, as well as two others. I'm going to need to see what that's about. I'm sure that'll be worse once I get the HV back up.

The tubes are largely original, almost all RCA. I'm hoping I just have a flat tube. I'll add the 6GU7's to the check list.
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Old 10-09-2015, 01:18 PM
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Something tells me this tube shouldn't be so... crispy...and dark. The camera can't even pick up on just how bad it actually is looks.

This is the 6EL4 tube. It's also RCA original.

Last edited by Arcanine; 10-09-2015 at 01:23 PM.
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Old 10-09-2015, 01:48 PM
DaveWM DaveWM is offline
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tube dark from xrays, just means had a lot of use, does not mean bad.

you should 1st try running the set with the CRT plug (the base socket)disconnected, this removes the load of a CRT which may be high due to bad CRT or incorrect bias.
Check HV

if no change, then try disconnect the 6Bk4, this takes the shunt tube out of the circuit, could be a prob if bad or bias is wrong.
check HV

if still no change
Check Horz out voltages, screen and grid
Check Horz out cathode current
Report back findings for whats next.
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Old 10-09-2015, 02:06 PM
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Quote:
Originally Posted by DaveWM View Post
tube dark from xrays, just means had a lot of use, does not mean bad.

you should 1st try running the set with the CRT plug (the base socket)disconnected, this removes the load of a CRT which may be high due to bad CRT or incorrect bias.
Check HV

if no change, then try disconnect the 6Bk4, this takes the shunt tube out of the circuit, could be a prob if bad or bias is wrong.
check HV

if still no change
Check Horz out voltages, screen and grid
Check Horz out cathode current
Report back findings for whats next.
CRT plug disconnected: 14kv

6BK4 Disconnected CRT plugged in: 14Kv

I'll have to check the other two after my trip to see Jim.

I made sure I had a stonger connection with the probe today, the set is managing 14Kv
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