Rca ctc-5

[Penthode]

I made an interesting discovery today. I was troubled by the low grid bias on the horizontal output tube. This pointed to a slight reduction of horizontal drive.

I examined the circuit of the 6CG7 synchroguide horizontal oscillator. Comparing with the CTC7 and CTC9, the plate voltage of the oscillator was a bit lower.

To increase the drive, I thought I could raise the plate voltage a little. I discovered that R604 and R603 form a voltage divider. Further, I discovered my set had an 82K 1watt resistor for R603 where the schematic showed 100k. I tried substituting a higher resistance which raised the drive a bit. The offshoot is that the unregulated HV has gone up (good) and the grid bias on the horizontal output is now correct (very good).

Then after this, I read in the "Series 700 Setup-Service Manual" (available on at the ETF website), where, on the page 71 pictorial of the horizontal oscillator circuit board, there was a little note to the side of figure 132. It reads "Note: R603 may be reduced in value if less drive to horz. sweep output is desired".

So whadaya know?