My CTC-16XL Project.

[Yamamaya42]

So, I gather, tubes aside... that there is a higher probability that the old carbon core resistors could be out of tolerance than the ceramic disc caps, ( not that it can't be both :/ ) Which kinda makes sense, I had my Sansui 9090 go from working to non-working sitting in the same shed as the CTC, for a few years and had to replace several resistors on it to get it to come back up.

edit---
good thing to note, as I was poking around for info, I should stick with Carbon Composition Resistors if i do replace any, ( in the IF )
"Film Resistors-their frequency response is much worse due to the inductance and capacitance caused by the resistive path cut into the film."

[Phil]

40 mfd capacitors are available. Newark lists no fewer than 15 of them. I doubt the value is very critical.

[Electronic M]

The carbon comps are moisture sensitive...Storing them in a humid environment is pretty much the best way to force them to drift...Short of storing your set underwater.

The film types probably won't make a huge difference in the IF.

[Yamamaya42]

the carbon core ones i am seeing on Mouser are all 5% so I'm sure they will be better than the 10% that was in there.
And yes, it was stored in a shed outside, in central Texas, where it got as hot as 110f, cold as 18f and quite humid, but it was covered and protected.
So, with all that, I'll start with looking at the resistors in the If.

[Yamamaya42]

Oh yes, I definitely have some flaky resistors... I'm finding some wide open and others beyond 20% (some OK ) , will put some new ones in this weekend and see what happens.

[DavGoodlin]

The CTC16X is worth the effort. I had one and it made about the nicest picture of all my 60s'-era RCA sets, including a CTC38.

[Yamamaya42]

:d ammit:

Dammit dammit dammit!!!! BLOODY HELL!
Just when I get the IF section semi working..

I SEE snow on the screen ( with color ) I hear it in the speaker.

I go to hook something to tune in, click to the right channel, fine tune, I hear audio and POP, i lose raster...

WTF??.

quick check...

yes still have HV,, all tubes still lit, but something smells hot …

close look.

i lost 970v boost...
https://imgur.com/fZYxnRF
https://imgur.com/ZNpZOcw
why did it have to choose THAT MOMENT to fry?!?

[Electronic M]

Check the caps that filter the boost for shorts also check the line for shorts (such as tin whiskers on pots, insulation breakdown and such). Something caused that resistor to burn up like that.

Also, it may be wise to get a new boost diode. I've seen them fail more than once and what killed that resistor may have damaged the diode too...Radio Shack carries a 2A 1.5KV PIV diode that if you place 2 in series makes for a really rugged boost rect. Failing that similar specked diodes off the net will work.

My first roundy I came at the problem from the opposite direction. After fighting to get HV, and having sound, but no raster and chasing voltages I finally found my cooked boost rect...The hilarious part was that aside from no color and shrunken raster from dying caps the darn thing worked great on varic power up for a few secs before dying, and I never retested tube damper after power-up so after driving my self batty trying to get HV for a couple of months, and giving up I found the problem robbing the tube for another working set that had an intermittent damper arc.

[Yamamaya42]

Originally Posted by Electronic M

Check the caps that filter the boost for shorts also check the line for shorts (such as tin whiskers on pots, insulation breakdown and such). Something caused that resistor to burn up like that.

Also, it may be wise to get a new boost diode. I've seen them fail more than once and what killed that resistor may have damaged the diode too...Radio Shack carries a 2A 1.5KV PIV diode that if you place 2 in series makes for a really rugged boost rect. Failing that similar specked diodes off the net will work.

My first roundy I came at the problem from the opposite direction. After fighting to get HV, and having sound, but no raster and chasing voltages I finally found my cooked boost rect...The hilarious part was that aside from no color and shrunken raster from dying caps the darn thing worked great on varic power up for a few secs before dying, and I never retested tube damper after power-up so after driving my self batty trying to get HV for a couple of months, and giving up I found the problem robbing the tube for another working set that had an intermittent damper arc.

a tin whisker like https://imgur.com/eUeytX9 that..
so i guess that pot is shot..

[Electronic M]

I'm not sure if I'm looking at a whisker too thin to see, a really fat whisker or a normal part of the pot rotor.


The pot is not necessarily dead. They can be serviced. Verify the short on the boost, unsolder the pot leads and verify the short in the pot...If short is still present (and not the fault of the pot being set to min or max) on disconnected pot then unmount the pot, pry the tabs from the back cover that wrap around the front up till you can take the metal back cover off, verify the whiskers and what they are growing from, sand the growth surface lightly with very fine sandpaper till whickers are gone and surface is clean and shiny, remove metal particles with contact cleaner double check resistances are normal and reassemble.

If disconnecting the pot does not show the pot shorted but boost is still shorted keep tracing that short on the boost line.

[Yamamaya42]

Originally Posted by Electronic M

I'm not sure if I'm looking at a whisker too thin to see, a really fat whisker or a normal part of the pot rotor.


The pot is not necessarily dead. They can be serviced. Verify the short on the boost, unsolder the pot leads and verify the short in the pot...If short is still present (and not the fault of the pot being set to min or max) on disconnected pot then unmount the pot, pry the tabs from the back cover that wrap around the front up till you can take the metal back cover off, verify the whiskers and what they are growing from, sand the growth surface lightly with very fine sandpaper till whickers are gone and surface is clean and shiny, remove metal particles with contact cleaner double check resistances are normal and reassemble.

If disconnecting the pot does not show the pot shorted but boost is still shorted keep tracing that short on the boost line.

there is a really fat white strand on the blue screen pot, where the 970v hooks to it to the can of the pot that should NOT be there,,, hard to get a good pic with a cell cam :/

[Yamamaya42]

Originally Posted by Yamamaya42

a tin whisker like https://imgur.com/eUeytX9 that..
so i guess that pot is shot..

BTW, My very first exp with a roundie was when I was very young, I'm now sure it was a RCA, CTC-10A ( The Sullivan ), I remember the metal, gloss black lacquered cabinet. It was given to my parents by my grandparents, I loved that TV...
It later developed sync problems and my dad never really put the effort into fixing it and threw it away, I never forgave him for it, they bought a tiny RCA 19 inch hybrid to replace it.
So when I saw the chance to get this CTC-16xl years later... I took it!

[mrjukebox160]

You DID notice the brown cap with the crack in it hooked to the boost diode as well right?

[Electronic M]

Originally Posted by mrjukebox160

You DID notice the brown cap with the crack in it hooked to the boost diode as well right?

Yeah, that maroon drop C140? does indeed look damaged. Don't discount those maroon drops as being reliable...While some are still doing okay several have reported finding them drifting in value or even leaking (I've certainly found at least one leaking current)...

Here is a possible cause of that resistor failing: C140 started leaking current badly overloading the boost rect diode causing it to short, the rect then passed ~1KV AC pulses to the boost line. The boost is resistively connected to the 400V B+ rail and on negative 1KV swings of the horizontal feeding the shorted boost diode it started passing too much current through that 100K resistor frying it. Should be easy to check by ohming out the rect in both directions and testing that cap.

[Yamamaya42]

Yeah, that diode and cap are toast..
its a bit hard to find replacements using part numbers from a 50+ year old list, ( the resistor is easy )
i have picked mouser # 80-PHE450SB4220JR06 for the cap, and 625-RGP25M-E3 for the diode, i should prob replace that big cap and the little .001s on the screen pots, but they are most likely OK