Rca ctc-5

[miniman82]

Originally Posted by Penthode

I found the 6BK4 regulator is not really regulating the HV. This appears because the HV unregulated (with the 6BK4 cap off) is only about 23kV. When increasing the brightness hence the beam current in the CRT, the HV sags below 23kV.

As Wayne pointed out, I think you're misunderstanding how the 6BK4 does what it does. It doesn't tell the flyback to 'make' more power, which is what I understand when I read your post, it's only there to provide a constant load on the flyback. The flyback always operates wide open, only thing that can drag it down is the CRT or the 6BK4. When beam current at the CRT is low (dark images), the 6BK4 picks up the slack so to speak. When beam current at the CRT is high (bright images), the 6BK4 will be cut off. In this way the load is always constant on the anode, but if you ask me it's a pretty crude and wasteful way to do things.

Here is what I'd like to test: if the focus voltage does not track with the HV eg the focus voltage remain constant with the HV dropping, this means it is an unregulated HV supply issue.

Regulation isn't the issue here, since the 6BK4 only absorbs 'excess' HV when the CRT doesn't need it. The issue is lack of sufficient headroom in the HV supply to begin with, which explains why the chassis works the same wether the regulator tube is installed or not. It made little to no difference to the images on screen for me, there's just not enough HV to make a difference. Other sets will overshoot by a lot without the regulator, my CTC-9 for example would hit nearly 32kv unregulated. In that situation there would be a difference in images on screen, but not the anemic CTC-5.


Do the variac test, see what happens.