Rca ctc-5

[DaveWM]

Nice catch I will check that before I take the chassis off the bench

glad to hear about the pot fix, i was wondering about how that conductive paint may work. I saved the bad pot after taking it apart, think I will try it as well.

[DaveWM]

reviewing the schematics I can see the ctc-5 has the 82k and the ctc-5N has the 100k for R603. I have a ctc-5N and it has the 82k, hmmmm.

the ctc-7 has a different setup, with a pot for drive adj, and a cap in series with the 100k/pot.

Question for Pentode, did you check the cathode current before and after the switch from 82k to 100k?

I had no evidence of a drive bar on my set so I may try changing the resistor if for no other reason to see if I can get that cathode current down. I still have to try it with with the new convergence pots so I can get a good reading in the cathode voltage of the horz out tube. It was high before, but I think that was just due to the increased resistance of the old pots. IIRC the called for cathode voltage is 7.5 v and I was at 12v. So will base line it with the new pots, get a revised cathode voltage, then experiment with the R603.

I did check the current (200ma) but the RCA schematic did not specify what it should be, just gave the cathode voltage. I suspect 200ma was about right but would like it to be a low as possible. I did adj the eff coil for the dip.

[Penthode]

Originally Posted by DaveWM

Question for Pentode, did you check the cathode current before and after the switch from 82k to 100k?

I ended up selecting 110k. This yielded -40 volts on the Horizontal Output grid as per the schematic. The cathode current measured 210mA.

I did check the current (200ma) but the RCA schematic did not specify what it should be, just gave the cathode voltage. I suspect 200ma was about right but would like it to be a low as possible. I did adj the eff coil for the dip.

With 7.5 volts on the cathode, and the cathode resistance to ground at 23.5 ohms (the 82ohm in parallel with the static convergence 100ohm pots), this equals 320mA.

I now measure 5.0 volts for the 210mA. I increased the drive well below the appearance of the drive line. The HO tube runs a bit cooler and I have better regulated HV.