Questions on a Magnavox CTC12 clone
 

I just want to ask a few questions to check and make sure things are ok with this set. First of all the set plays fine except for some minor ghosting in the picture which i'll dig into later. The set's HV is set to 21kv and is stable with good sharpness in the picture and no blooming. It has new focus and HV rectifier tubes and a new shunt regulator tube. The H out put and damper tubes test like new. The H efficiency reading is 160ma which i didnt know could go that low and still operate well but it does. It is supposed to have a new FBT and by the fresh looking solder joints i can go along with that.

My questions are first after the set has been running for about an hour, i have checked the temperature of the FBT and the doughnut is nice and cool but the core is hot to the touch. Is this normal? It does have some wax drippage. Second, i can see both the HV rectifier and the Shunt Regulators filaments glowing almost as bright as the Horizontal output tube for example. Is this normal? I always thought the glow from those two were supposed to be dim and is why i ask.

I want to thank you in advance for any input you can give me on this set. I just want to make sure things are on point before i put it in occasional service as i don't want to run it and do unnecessary damage to it.

Hey Tony any crawl in the picture? I had a Magnavox that had low readings. Efficiency was around that too. I dont know about the primary of the flyback.

I'm currently working on an RCA CTC-16 and the shunt regulator glows bright as well. I've recapped the power supply too. I dont remember a shunt being bright.

Have you felt any of the filters to see if they get hot?

As you can see from this thermal pic from my CTC-16XL (same shunt) it does get very hot.
https://imgur.com/3hZnlmW

you can see it shining bright, behind the cage.

21KV sounds low. Do you have a service manual with the correct spec? If it is low try to adjust the HV reg give the manual specified HV....If it won't go that high see if it goes higher with the HV regulator top connection removed...If it exceeds posted specs with the HV reg removed then the next step is to start servicing the regulator circuit to get it into a state where it can hold the HV on spec.

Low HV due to reg issues strains the fly in shunt reg sets like most RCAs, and accelerates cathode wear out in the CRTs of all sets...It also has no merrits to balance it's risks.

I have a Sam's for it that i can dig out and get the right spec. The HV adjustment is only set halfway so i'm sure i can get a little more out of it. There is no crawl in the picture and all of the filters are cool to the touch even after hours of playing time. The picture is perfect except for some minor ghosting with good sharpness and no blooming at high brightness. It's been awhile since i worked on one of these and wanted to see what you all thought and see if my concerns were valid.

I'd look in the IF section. an out of tolerance resistor or a faulty delay line. How is the video detector tube? Is the smear also a certain color or just grey? If color smearing, could be in the chroma circuit.

Oh yea. Make sure the shield over the tuner tube (s) are up and shielded. I had this happen to me once. Oddly I believe it was a Magnavox roundie

I'll check the IF section and the video detector tube once i know it's safe to run in its current condition. The ghosting image is a transparent grey and is about an inch wide beside the main image. It doesn't move with adjusting the fine tuning. My main concern at the moment is like with anybody who has one of these early sets is the flyback.

Dont quote my but I believe you should be looking for minimum of 25kv at min brightness. Too low will overheat the flyback hljust as too much ma draw on the horizontal cathode efficiency would do. Also you should monitor the grid voltage of the h output tube as well for I believe-55 to -60v at pin 2 or 6.


This is all of course going off my notes I have made in the past.