CTC-20C for the record

[marty59]

I want to share my receint acquisition, an RCA model GH630W chassis CTC-20C. I know we discuss ways of ID'ing as well as justifying their reason for being the last RCA Roundie. IMO other than maybe a large stock of CRT's I believe these sets existed mainly as a low(er) cost alternative to the new square tube sets. Heck, there were not any remote sets made and few models at that, either a 20A or a 20C chassis design. I'm not sure if the differences were in the tuner/bezel layout? Other than on the front of the Howard Sams most of the one's I've come across look like the later CTC-16Xx style with a later channel selector knob. Plus, the chassis was backwords engineered from the squaretube CTC-19, which was a 19" set. I was still a kid at the time so I don't know what the cost would be for these when new, besides my becoming awareness of roundies...

Anyways my interest in picking up this set was for the CRT, which fortunately tests uniform with tracking ability but on the low side of emissions which is just fine for now. It had seen power and I was told that the screen didn't light up. It still had the original 6BK4 which had turned that nice brown charred color. I checked all the tubes and with a couple of exceptions removed the weak ones and especially any that checked with shorts. The Flyback has lots of drippings but I variaced it with the HOT out and then installed it. I was surprized to see a raster! (with no RF source). The Fly was staying cool too!!

But there are some issues with it, two of the legs had been JB Welded and the cabinet sides may have seen some moisture and gouges as well as something being spilled over the speaker area on the bezel. And the wicker basket grills do nothing for me! The top is nice though. Electronically, there may be some AGC problems as there is a lack of a snowy raster or sound but I don't want to force any fine tuning as it will only turn so much. I'll hook up my tuner subber and try to pass some RF through it at least. I just want to check it out but not make any repairs.

My plan is to remove the tube and do my first cateract repair. This tube tests better than the one in my Zenith 5131 chassis 25LC30 so I want to make sure I have a spare. I've started on another set so the Zenith will be waiting some. I'm not making any drastic decisions at this point but I wanted to post some pictures since we like to look and talk about roundies!

[Kalamazoo-DJ]

very nice!

[ctc17]

That set will produce a better picture, better color than the Zenith. Thats my experience so far. The flyback could be an issue if it arcs out.
The cataract is going to take some time in water. The edges look real bad but a good portion of the middle still looks solid.
If it was me I would lean towards getting that RCA working good rather than just use it as a doner.
The cabinet isnt super sexy but the picture could be impressive. That thing working well is a real conversation starter.

[marty59]

I can understand what you are saying about the RCA. I have a CTC-16E that I've had since the mid-late seventies that has a good picture with vibrant color. During my tech school days it was the "house set" and it would impress whoever came in the door. Plus, knowing a thing or two about setting up a receiver didn't hurt either!

I did a side by side comparision with it and a Zenith 24MC32 that I had at the time. The RCA did seem to have the edge with color being more vibrant whereas the Zenith video was a little sharper, detailed.

But dang...They both looked great even next to each other that you wouldn't have walked away from either one!

As for that Flyback on the CTC-20, with some good flowable silicone and the fly removed and on it's side, I'd pour some of that through and save it before it would get any worse. I've had good results with Permatex Windshield and Glass Sealer. The stuff is super flowable to get in-between the windings and won't burn your eyes and nose. I did my Predicta with it.

Speaking of silicones, is it the acetates that are so strong smelling and irritating?

[miniman82]

I used sensor safe silicone, it's not supposed to damage electronics.

[VintagePC]

Originally Posted by marty59

Speaking of silicones, is it the acetates that are so strong smelling and irritating?

Yep. If I recall correctly, the silicone (especially caulks) are set by the moisture in the air that polymerizes the compounds present. Acetic acid (that vinegar-y smell) is produced as a result, and can be very irritating.

Household vinegar is quite dilute acetic acid... if you ever get a whiff of the pure stuff (called "glacial" acetic acid)... Hooboy, does that ever clear your sinuses!

[Phil Nelson]

I'm guessing it won't require much work to have that looking good after you fix the cataract. Seems too nice to tear up for parts. I actually like the basket weave grille with vaguely Danish style legs. It's amazing what people use JB Weld for.

Not an expert on flybacks, but I recently used sensor safe RTV to coat a 1950s Philco flyback and it's holding up OK.

Phil Nelson

[old_coot88]

Any of you ol' RCA mavens remember that factory-issued field mod to the CTC-20 for weak vertical sync? It involved changing two resistors in the sync separator section. They were half-watters somewhere between 270K and 680K, IIRC.
Bill(oc)

[vintagecollect]

Interesting set,

I've seen old ads somewhere of $495 specials for lower end roundies. I doubt this was too thrifty, NICE cabinet quality. Dial and benzel very similiar to early RCA SS. This is a unique transition piece before ss.

DOES this have any ss components??? It only helps with reliability.

[marty59]

Originally Posted by vintagecollect

Interesting set,

I've seen old ads somewhere of $495 specials for lower end roundies. I doubt this was too thrifty, NICE cabinet quality. Dial and benzel very similiar to early RCA SS. This is a unique transition piece before ss.

DOES this have any ss components??? It only helps with reliability.

Not really except for diodes in the usual places: LV and B+ Boost rectifier, detector stages. But it does have a transistor in the UHF Tuner which had become standard practice by this time.

These sets were produced around the 1966 timeframe. This one that I have has date codes of 66-30 on the CRT and the tubes were earlier . The Howard Sams was published 9-66 as folder 837-2.

[ctc17]

My idea for rewaxing flybacks is to remove the tire, submerge the coils in a pressure cooker full of molten wax, put the lid on, pull the pot into a deep vacuum for a few minutes then slowly release vacuum remove lid and coils and let cool. That should get all the air out of the coil. Its basically how the factory does it.
I dont care if its dangerous, Ill do it outside with the proper protection.

[Findm-Keepm]

Originally Posted by miniman82

I used sensor safe silicone, it's not supposed to damage electronics.

That's awesome that they've come out with a commercial RTV that is "electronics safe" - for years, the only safe RTV was good ol' Dow RTV3145 that we used to get at the DRMO sales. Expired shelf life for the military was taken seriously back then - now, because of costs, they extend it liberally beyond the manufacturers data. RTV3145 is Mil-spec, UL Listed, and expensive - about 24 bucks a tube, enough to fully coat a flyback.

I guess sensor safe RTV is obtainable at auto parts places? Gotta look next time. I have a spare flyback (or two!) for my CTC-16 roundies and my portacolor, but to spare a flyback, I may go with sensor safe if ever the need.

Yet another VK educational moment!

Cheers,

[ctc17]

Sensor safe silicon is referring to the oxygen sensor in vehicles only. Oxygen sensors are easily killed by a few chemicals. One is the coolant in the vehicle, thats why a head gasket failure can kill the 02 sensor the other is whatever chemical they use in cheep silicone.

[AUdubon5425]

Originally Posted by ctc17

Sensor safe silicon is referring to the oxygen sensor in vehicles only. Oxygen sensors are easily killed by a few chemicals. One is the coolant in the vehicle, thats why a head gasket failure can kill the 02 sensor the other is whatever chemical they use in cheep silicone.

I can second that statement.

[Phil Nelson]

Originally Posted by Findm-Keepm

I guess sensor safe RTV is obtainable at auto parts places?

Here's the stuff that I used. (This is a "before" photo of the flyback.)



Phil Nelson