CTC 5 Low high voltage

[oldtvsandtoy]

aaa?

[DaveWM]

a few things, shunt tube connected (not malfuctioning), CRT not drawing excessive beam current (bias correct, no shorts in grids). Horz freq correct? B+ correct at the plate of the HOT, Screen voltage and HOT bias voltages correct, Correct drive form.

I would start by checking the HOT current by checking the V drop at the cathode fuse as specified.

[DaveWM]

oh test the B+ at the plate cap with the plate cap OFF and the tube out of the socket. with no load it should be very high, not a great test if you are getting some HV but a starting point. Really a better test for no HV.

HOT screen voltage will tell you a lot. tube 6CB5 pin 1 or 8 (screen) should be 172vdc, pin 3 or 6 (cathode) should be 7.5v and pin 4 or 5 (control grid) should be -40v

for testing the SHUNT TUBE you can siimply disconnect the 6BK4 plate lead (keep it clear of any ground, this will have FULL HV on it so be careful. disconnecting it will clear the shunt tube as a problem (if the HV comes back that is).

[DaveWM]

also is the flyback transformer getting hot (wait a few min to touch it AFTER power off) Any time you are working on HV I recommend just leaving the HV prob attached so you can always confirm if HV is present even after power off.

[oldtvsandtoy]

aaa

[miniman82]

Run through the horizontal section alignment procedure in Sams, that usually clears up some problems. If frequency is on point, you have good B+ to the plate cap on the horizontal output tube, the HV rectifier is good in another set (don't trust the tube tester on this one) and the fuse isn't blown, you might be looking for a new flyback.

Pull the shunt reg cap off the 6BK4 and disconnect the HV anode wire to the CRT. Still low? The problem is in the chassis. FWIW though, no CTC-5 I've ever seen had good HV. Mine maxes out at 21kv, and I modded the chassis with pots to control shunt tube grid bias and horizontal drive.

[bgadow]

Do you have a scope? I'm no good with one, but used one to tune up the horiz waveforms on my CTC-5 and it helped, though mine still runs low (maybe 19k). I stopped worrying about it because it puts out a nice picture. Be careful tweaking those coils, you can easily crossthread the cores on some of them.

[oldtvsandtoy]

aaa

[oldtvsandtoy]

aaa

[radiotron]

Originally Posted by oldtvsandtoy

ok here is where I stand right now. I pulled the shunt reg cap off the 6BK4 and disconnect the HV anode wire to the CRT Still only 9k. I then put the chassis in my other ctc5 and the same thing. Only see 4 fuses, one being a piece of wire. All good. Flyback is not getting hot. How much can I check with the chassis out of the set?

do you think the yoke could have anything to do with it?
OR a break in the board, cracked solder etc.?

[oldtvsandtoy]

aaa

[oldtvsandtoy]

aaa

[Penthode]

Originally Posted by oldtvsandtoy

Ok I got around to checking the horz output tube. Here is what I found. With top cap off and tube removed, I get 416vdc at the cap.
pins 1 & 8 190vdc
pins 2 & 7 6.3vdc
pins 3 & 6 8.7vdc
Pins 4 & 5 -20.5vdc
Well 4 & 5 dont look right should be -40vdc So what do you think now?

Pins 2 to 7 should be 6.3 vac of course.

Pins 4 and 5 are the control grid. Without a scope it is hard to guess. But the bias is developed by the grid rectification and only -20vdc implies you are not getting sufficient horizontal drive or else the coupling capacitor is leaky.

Then again, you may not be getting sufficient horizontal drive. A scope would sure help the diagnosis process.

[DaveWM]

a few things, did you replace the .01 cap that could be leaky that goes to the grid? did you replace the 2mf electrolytic cap on the video board? Agree with pentode a scope reading of the grid of the horz out would tell a lot. the -20 was with the tube in correct? and what kind of meter were you using to check it? VTVM's are the best, a DMM will prob be ok but a VOM would be too much of a load.

[DaveWM]

oh and you did do a tube swap from a KNOWN working set, all HV tubes (horz out, damper, HV rec, shunt) and the horz osc tube as well.