Today's Mystery Guest (RCA CTC-4)

[jr_tech]

I suspect that the xtal substitution will answer the question, but then I was wrong before about your CT-100 xtal

Be careful soldering to the pins, heat sink them if you can.

jr

[Phil Nelson]

Well, I subbed two different 3.58-mc crystals and took care not to overheat their pins.

No change in symptoms. I'm still lacking the negative voltage on pin 6. Still seeing the greenish color bars that disappear when you turn the Color control down.

Seems unlikely that all three crystals would be bad, although I guess anything is possible.

Phil Nelson

[miniman82]

Ignore the reactance tube for now, or at least keep the input grounded for the moment per the adjustment procedure so you can focus on getting the oscillator running. It's obvious you have no output from it, that's why you have zero grid volts on V124A and also sagging plate volts- that tube is probably turned on 100%. Make sure the .01uf caps to ground coming off pin 2 are not leaky (C2110/C211), then see if you can lift one of the primary winding wires of T115 (pin B or E) and measure resistance. It's possible your CW transformer has shorted or something, but tuned circuits can be deceptively hard to troubleshoot despite their apparent simplicity.

One last note: although the inductors in the CTC-4 chassis are not the dreaded white ones that always go bad like the CTC-2(B) chassis had, it's always possible you have a bad inductor still. Make sure L42 checks in at the proper resistance, and also ensure C209 isn't leaky.

[Phil Nelson]

Thanks, we hear and obey

Phil Nelson

[old_coot88]

There's also a couple of .001 caps (C219 and C220) across the secondaries of the CW xfmr. One of those could be wonky.

[Phil Nelson]

I believe C219 and C220 are inside the T115 can, but as chrisWA6TV mentioned, little micas inside xfmr cans have been known to go bad, especially the "naked" kind that are uninsulated mica sheets. I replaced some in the audio section of an Admiral set.

My back is just about played out for the day. Tomorrow I will grunt the chassis back onto the workbench and go on a cap-and-resistor hunting expedition.

miniman82 mentioned C209, which I already replaced, but that reminds me -- depending on what schematic I look at, that cap's value is given as 4, 4.7, or 6.8 pf. Here's the C209 that I removed:



I hate the codes on these little dogbone-shaped caps (and I have never found a bad one, but I replaced it anyway, while I was soldering on that terminal). What I had on hand was a 5 pf mica, so that's what I installed. I'm hoping that this code translates as 4.7 pf and that a difference of .3 pf doesn't matter here. If I'm wrong on one or both counts, someone tell me now, and I'll just put the old one back in.

Phil Nelson

P.S. The resistance across L42 is 10.6 ohms, which doesn't seem outlandish. The schematics don't give a resistance for it, only the notation 12 muh.

[old_coot88]

The schematic indicates there should be three ferrite slugs inside the CW xfmr. Are all 3 present and intact? No doubt they've been diddled with if somebody's been in there before.

Also, you stated R246 is 22K, where the schematic shows it as 2.2K.
Is the replacement red-red-orange (22K) or red-red-red (2.2K)?
In any case, that would not stop the oscillator from running.

[Phil Nelson]

You're right, it's 2.2K (red-red-red). When I lose the ability to read and type, that's a sign to break for the night

T115 has one adjuster slug accessible from the bottom and a second accessible from the top. The RCA manual says that the bottom adjuster is used in color AFC alignment and the top one for B-Y phasing. Both slugs are present and can be moved (the settings may be completely wrong, of course).

The Sams schematic seems to show that the two secondaries are adjustable, labeling them A64 (top) and A60. No label is given for the primary. I don't know why the primary is shown with an "adjustable" symbol if no adjuster is accessible.

Phil Nelson

[old_coot88]

Could it be a slug is missing from the primary? Or is there a big enuff hole to allow its exit?

(Edit) On second thought, it does look like an untuned primary, since there's no cap in parallel with it.