CTC 5 Low high voltage
 

aaa?

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.

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).

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.

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.

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.

aaa

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do you think the yoke could have anything to do with it?:scratch2:
OR a break in the board, cracked solder etc.?

aaa

if it is its proboby right under the hv cage i would look at all the retrace lines around there then try that:smoke:

best way to trouble shoot HV would be to start with voltage readings on the horz out tube. the 5 has a 82 ohm resistor in the cathode circuit, and pulls cathode current thru the static converge pots. Get a resistance reading on the cathode pin of the tube socket and I will compare one of mine (or if you have a SAMs see if there is a resistance chart you can check). besides drive issues (which I doubt you have if the fly is not getting hot) You should check the screen voltage and with the plate lead disconnected and the tube pulled, check the Hor out plate cap lead and see if you have full B+ there. You did say you subbed known good tubes for horz out/damper/shunt/focus?

aaa

I would think you can do it all as long as you hook up a yoke and convergence coils

Correct

are you SURE you didnt put a cap in backwards?

aaa

resistance reading
 

aaa

By "plate cap", DaveWM didn't mean "plate capacitor", but the physical connection "cap" on the top of the 6CB5 horizontal output tube.

Pull the 6CB5 out of the set, and measure the DC voltage on the wire that was connected to the top of it. Should be +375V or so. DO NOT try to measure this with the tube installed, as the high voltage pulses normally present will fry your meter!

Put the tube back into the socket, reconnect the plate lead, and measure the voltage on the screen grid (Pins 1 and 8). Should be about +175V.

Check the voltage on the cathode (Pins 3 and 6). Should be about +7.5V.

CTC 5 Low high voltage Update:
 

aaa

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.

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.

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.

The high cathode current and low grid voltage sure sound like low drive.

You really want a scope at this point. An external drive source like a 1077B or VA48/62 would be a great help, as well.

Start checking resistors and caps in the horiz osc. circuitry.

good point about using an BK analyst, those are great for these kinds of problems. You can quickly clear the fly with the plate drive and then move on to the grid drive to check the horz output tube. I picked mine up for 9$ IIRC, fun to have and you can make neat shadow puppets with it too :D

aaa

It is just that if the horizontal drive is low, then the resultant bias will also be low. That is because the bias is derived from the drive amplitude: eg a proper level drive will give higher bias. And the low drive would reduce the high voltage substantially.

what is pin 6 of the 6CG7 (horz osc tube), should be 235vdc, there is a voltage divider network made up of a 39k and a 82k on the horz board, I would check there if the voltage is not right.

aaa

Check R606 (68K) and C606 (330 pF) on the horizontal PCB, as well.

The voltage divider resistors are R603 and R604.

aaa

those pn's are from the RCA service manual, its online a pdf. Sams will be different. Whats nice about the service manual is the show the schematic on the PC boards so you know where the parts are located.

was discussing this with another member, a freq counter would help since you don not have a scope, just in case you are way off freq. After checking the horz freq parts already mentioned, see if your meter lets you do a freq check.