Ok. Let’s try this again…RCA 9TC240 Alignment

[Chris K]

What kind of potentiometer? A variable resistance pot? In what range? How do you use it in a way that makes connecting it in the sockets secure while you adjust it? Do I need to build some sort of rig/tube base with a pinout?

[Penthode]

Originally Posted by Chris K

What kind of potentiometer? A variable resistance pot? In what range? How do you use it in a way that makes connecting it in the sockets secure while you adjust it? Do I need to build some sort of rig/tube base with a pinout?

It is effectively a rheostat or variable resistance. Just wire two leads to the pot wiper and element end and attach it to the pins five and six. I typically take a longish cheap croc clip lead, cut it in two, solder it to a pot and then clip the leads to pins five and six.

[Penthode]

It says what it is in the manual doesn't it? 250k or something like that? (I don't have the manual in front of me at the moment).

[Chris K]

Originally Posted by Penthode

It is effectively a rheostat or variable resistance. Just wire two leads to the pot wiper and element end and attach it to the pins five and six. I typically take a longish cheap croc clip lead, cut it in two, solder it to a pot and then clip the leads to pins five and six.

I’ll have to look closer for the resistance value. I don’t have any pots that go that high so I’ll need to check the Riders before I order one. The clip lead idea sounds doable. I was thinking of getting fancy and getting a test adapter for the socket wiring the pot to that.

[Penthode]

A real cool way if you were doing lots of these sets would be to use and old octal tube sockets with pins five and six wires to the rheostat. Then all you would have to do is just remove the tube and plug the rheostat in

[Chris K]

Originally Posted by Penthode

A real cool way if you were doing lots of these sets would be to use and old octal tube sockets with pins five and six wires to the rheostat. Then all you would have to do is just remove the tube and plug the rheostat in

Yeah that’s what I’m thinking about because I have about a dozen RCA sets in storage none newer than 1950. Today I picked up a 1949 Emerson and a Dumont RA103-A with the FM radio and a CRT I’ve never seen before, a 15DP4. It tests great…almost new. One owner set.

[Penthode]

Note for the trap adjustment with the VTVM across the video detector load resistor, the case of the VTVM must not be grounded to the mains supply ground. That would have to be lifted. You can be cautious and do it this way. Or alternatively if you have a digital meter that measures trends rather than just an absolute, that may be safer.