Capehart 325 restoration

[HighHopes]

Hi Bob,

I have a question about the small test CRT tubes you use. After you get a set to work with a test tube, do you need to readjust the set again when the full sized tube is installed?

Also, I am thinking these tubes do not use an ion trap, true?

Is the focus coil a problem?

Steve

[bandersen]

Originally Posted by robert1

since i don't have a diagram to look at for that chassis, i could only ask a couple of things. is the horizontal drive control a adjustable coil?, or a variable capacitor? or a pot? if it is a coil type, usually, those have a capacitor across it. it might be leaky. the coil itself, may have shorted windings.

have you checked the current on the cathode of the 6BG6?

i still suspect that red disk capacitor underneath the damper tube socket.
it appears to me that something is drawing too much current in the output stage. it might be that the flyback xfmr may a a few shorted turns or any of the above mentioned things, it also could be caused by a problem in a different circuit protected by that fuse.

You can download a copy of the Sams here: http://www.earlytelevision.org/pdf/C...Sams_160-2.pdf

The drive control is a pot. I'll try replacing the cap and measure all the voltages and waveforms in the horizontal circuits..

Originally Posted by truetone36

Nice to see you making progress, even though there's been a couple of bumps along the way. When you get the bugs worked out, shoot me a PM and I'll get those knobs and the nameplate/control cover out to you.

Thanks, I sure will!

Originally Posted by HighHopes

Hi Bob,

I have a question about the small test CRT tubes you use. After you get a set to work with a test tube, do you need to readjust the set again when the full sized tube is installed?

Also, I am thinking these tubes do not use an ion trap, true?

Is the focus coil a problem?

Steve

Yes, you need to readjust, the height, width, linearity etc. They do not use an ion trap and are self focusing.

Leaving the focus coil in place does produce a blurry image. That's why when I unmounted it in the photos above the picture improved.

[robert1]

Originally Posted by bandersen

You can download a copy of the Sams here: http://www.earlytelevision.org/pdf/C...Sams_160-2.pdf

Thanks!, Bob

Originally Posted by bandersen

The drive control is a pot. I'll try replacing the cap and measure all the voltages and waveforms in the horizontal circuits..

Acording to the diagram, that .25 amp fuse protects the screen grid on the 6BG6. it also supplies voltage to the horizontal drive control as well as the damper circuit. the first thing i would do is place a milliameter between the cathode of the 6BG6 & the -100 volt source that is currently connected to the cathode of the H.O.tube. power the set up & monitor the meter reading. if it is rising & starting to go over 250Ma, it is possible that the 6BG6, itself, has developed grid leakage that does not appear when it is cold. you can also sub another 6BG6 to see if it does the same thing.

about anything could be causing the fuse to blow, however the most obvious things would be the H.O.tube, the horizontal drive pot that has "whiskers" in it, the Screen resistor (r88 22k) that has lowererd it's resistance.
i would check these things first.