Another RCA CT-100 discovery B8001599

[Tom9589]

Have you ohmed out the vertical convergence transformer for shorts and opens yet? IIRC the original transformers were painted black while the modern reproductions were silver in color. You might have gotten lucky and have a reproduction.

[Electronic M]

I forget what the case was on my CT-100 (I think the previous owner addressed the power supply when they did a janky amateurish recap), but my 21CT55 (CT-100 factory modified to drive a 21AXP22) both ballast sections were open so I bought a couple of chassis mount high power resistors off mouser and found places on the rear upright where the resistor screw holes lined up with the cage screw holes. I gutted the original ballast and it now exists purely as decoration.

I also ended up replacing each selenium with 12 modern silicon diodes in series to emulate the original selenium voltage drop.

[Jeffhs]

Originally Posted by Electronic M

I forget what the case was on my CT-100 (I think the previous owner addressed the power supply when they did a janky amateurish recap), but my 21CT55 (CT-100 factory modified to drive a 21AXP22) both ballast sections were open so I bought a couple of chassis mount high power resistors off mouser and found places on the rear upright where the resistor screw holes lined up with the cage screw holes. I gutted the original ballast and it now exists purely as decoration.

I also ended up replacing each selenium with 12 modern silicon diodes in series to emulate the original selenium voltage drop.

It was a very good thing you replaced the selenium rectifiers with modern silicons, as seleniums can short and give off a very unpleasant-smelling gas when they fail.

I did not realize, however, that you needed to replace the selenium rectifiers with 12 silicon diodes, for a total of 24 silicons. I am thinking your TV used two selenium rectifiers, as a lot of 1950s TVs did; my folks' second TV, a Crosley Super V from about 1955, had two seleniums in the LV power supply. (Their first television, a 1954 RCA Victor 21" console, had a 5U4 LV rectifier, IIRC.) These selenium rectifiers, IIRC, were still good when we finally put the Crosley Super V in the basement in 1965 (where it, and the cabinet of the 1954 RCA, remained until 1972; long story and OT), replacing it with a Sears Silvertone all-channel 17-inch b&w portable shortly thereafter (at my mother's insistence, as she wanted an all-channel TV by this time; the reasons for that are OT for this thread).

Now that your TV has silicon LV rectifier diodes to replace those seleniums, you won't have any more trouble with the rectifiers for a long time unless they short again, giving you one less thing to be concerned about. However, this shouldn't be an issue; if the rectifier diodes short again, the TV's line fuse(s) or circuit breaker, of course, will open immediately, so you will know beyond the shadow of even the most unreasonable doubt that there is something wrong in the power supply.

[Penthode]

Originally Posted by Tom9589

Have you ohmed out the vertical convergence transformer for shorts and opens yet? IIRC the original transformers were painted black while the modern reproductions were silver in color. You might have gotten lucky and have a reproduction.

Yes that was one of the first thing I did. I lifted the secondary and did not see the VTVM needle quiver which suggests the leakage resistance is greater than 1000 Mohms.

[Penthode]

Only received the rivets for the tube socket remounting yesterday. The rivets are 3/32" x 1/4" and the 1/4" length was needed for the phenolic wafer socket + tube shield bracket + chassis thickness. Had to drill each rivet core by an additional 1/32" and reduce the diameter of rivet head from 0.200" to 0.150 to match the original over heads.

Supported the front chassis section with books and a punch was clamped in a vice below the chassis for the head of the rivet to rest. Then used the hammer and rivet tool on the topside to spread the rivets. Two sharp taps and a couple of finishing tops to ensure the tube socket is firmly secured.

The tube sockets are back in place and along with the IF and Audio Ratio Detector transformers. Currently replacing the potentiometers and soon will commence rewiring.

So much cleaning to get rid of the mess left by the previous tenants. Looking much cleaner now. And in case you forgot how bad it actually was, go back to page two of this thread to have a look!

[Penthode]

This week's update: I have completed the reinstallation of the video and sound IF and audio amplifier wiring to the previously mouse encrusted region. I am awaiting a couple of capacitors and that's it. I shall reattach the front section of the chassis next week and reintegrate the two. I reckon it has taken about 60 solid hours of effort to get this far.

All of the resistors in the mouse infested area are new as are the capacitors. I reused the pots after dismantling and cleaning. All of the resistors are NOS old style brown body resistors.

The high voltage box which was removed has been cleaned and all capacitors (apart from the doorknobs) have been replaced.

Have been meticulously following the dozens of photographs taken from different angles as well as refering to the schematic to confirm connections. I took copious notes when dismantling but have hardly needed to refer to them.

Still have to finish replacing the paper dielectric capacitors on the front section and a large bunch on the main chassis.