10KV caps.

[JohnCT]

I'm triaging a 1951 Andrea to see if it's restorable (going to get it running first), and it has a three 10KV caps in it. Two are 470pf (this TV has dual 1B3s) and a 500pf which I assume is the doorknob. I haven't really gotten into it yet, just perusing the schematic.

Digikey has several choices for HV caps, what are some safe ones to use if I need to order some?

John

[Electronic M]

Doorknob caps have been made until recently and some are still available through mouser and digikey. I typically buy those and machine pegs to adapt their threading to the mounting style of the original doorknobs. They are expensive, but original and on the early color sets that comprise my main use case it is worth the investment.

If the CRT has good dag on it and there is a cap in parallel with the cap formed by the CRT dag then you can probably eliminate that cap.

May also be able to get away with leaded ceramic caps to save money, but I haven't tested any in that application yet to give any endorsements.

[Notimetolooz]

On some sets the caps are used to support the HV rectifier, so leaded replacements won't work.

[Electronic M]

Originally Posted by Notimetolooz

On some sets the caps are used to support the HV rectifier, so leaded replacements won't work.

If you replace the cap a with leaded cap and a plastic, ceramic or phenolic stand-off to mechanically support the socket in the same manner as the old door knob it would work. It would not look original, but would work.

Doorknob caps often do work, but a decent percentage of failures have been seen....If they are not known bad you could fix the rest of the set and see if they are ok.

[JohnCT]

The doorknob on this one is mounted on the flyback board and is not used as a standoff - just appears to be wired in electrically.

John

[JohnCT]

I decided to move along a bit on the Andrea, and brought her up on a variac. A can filter refused to reform and decided to puke itself, so I pulled the 40/500 - 40/500 and restuffed it.

I found the B+ normal and nothing running hot. The HV was around 1500v, so I checked the two 1B3 rectifiers, damper, and horiz output tubes. Interesting, this TV uses two HV rectifiers as a doubler - something I'd never seen before. I image the plan is to improve the reliability of the flyback.

The tubes checked good so I pulled the two 470pf 10KV caps I suspected might be an issue at 70 years old:



I found one reading very little capacitance and some leakage at 600V (the most my Z meter will provide) and the second one decided to become a 15 ohm resistor.

Probably explains my low HV...

I'll take the doorknob out next and check that. I'll order some ceramic caps and see if she'll run.

John

[JohnCT]

I've ordered some 470 10KV caps to replace the leaky/shorted ones, but was wondering what a nominal HV reading should be with a 16GP4 tube. Should I expect around 15K give or take?

John

[Tom9589]

Per the GE Tube Manual, typical anode voltage is 12KV. Design max is 14KV.

[JohnCT]

Originally Posted by Tom9589

Per the GE Tube Manual, typical anode voltage is 12KV. Design max is 14KV.

Excellent. Thanks for the info Tom. The Sams makes no mention of nominal anode voltage, and I've never worked on a TV this old.

John

[JohnCT]

Minor update. I ordered some 470pf 10KV ceramics and installed them on the flyback in the voltage doubler circuit (two 1B3s in this TV), and I get 12KV now, which according to Tom, is right in the ballpark.

I have an image of sorts, but it's extremely overdriven. In fact, with the brighness control anywhere except all the way down, it blooms to the point of HV loss. It also has short vertical deflection.

There are some .05s which are clearly leaky in the chassis as they are throwing the DC voltages of is several circuits, but what's odd is the extreme ringing visible:



Hoping the ceramics in place of the 10KV film caps aren't causing issues.


John


EDIT: the raster is actually full horizontally. If I adjust the contrast, the screen will wash out and fill the screen, although it remains darker on the right side. The ion trap affects it but won't change what I see when the brightness and contrast show a clean snow pattern. Also, I don't want to shotgun this particular unit as I am am working through it as if it was a fairly new TV to bone up on my vacuum tube skills. I started in this trade at the end of the tube era but still worked on many through the late seventies.

Surprisingly, the CRT is strong. I found this TV with a brightener hanging off the back of the tube, and coupling with the fact that this metal coned beastie isn't known for a long life anyway, expected to find the tube junk. On my tester, it actually showed decent emission after about 10 minutes. When firing up from a cold start, I get a very bright partial raster in about 30 seconds, so I think I'm good on the tube anyway.


.

[Electronic M]

If there is a B+ boost line that is powered by the flyback I'd make changing any paper cap connected to it my first priority for replacement....It could be causing all problems you're seeing.

[kramden66]

Is that the Andrea model tv16 or something like that ?

[JohnCT]

Originally Posted by kramden66

Is that the Andrea model tv16 or something like that ?

It's a cvl16, or at least the table model version.

John

[JohnCT]

Originally Posted by Electronic M

If there is a B+ boost line that is powered by the flyback I'd make changing any paper cap connected to it my first priority for replacement....It could be causing all problems you're seeing.

I didn't change any papers around the damper yet, but I brought home my backup scope from work, and there's a nasty pulse modulating the video at the horiz rate, so there's an open bypass in there.

I'll get back to it Saturday unless my brake job on my truck runs into Murphy's Law..

John

[Tom9589]

Murphy always comes visiting during brake jobs. It's one of his favorite things to screw up.