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[Electronic M]

Originally Posted by timmy

So with doorknob capacitors, how can you tell if they are going bad , like symptoms, since you really can't tell by just checking them without hv running threw them. Do they become intermittently problematic ?

I've seen doorknobs dead short on a dime and I've seen them go flakey where the HV will fluctuate between almost normal and dead (horizontal will act flakey due to the extreme load fluctuations)....

If there is dag on your glass CRT and it is grounded then you can remove the doorknob and power the TV to test it (the doorknob is likely redundant). If the set opperation improves substantially the doorknob was bad.
If you disconnect it put a glass or ceramic ( a jar or coffee mug often works) insulator in place to prevent the disconnected end from arcing.

In the early 50s many sets that didn't need a doorknob would have one.... many TV makers would have one chassis drive a wide variety of CRT sizes and if one of those CRTs was metal then every chassis made would have a doorknob.

[timmy]

So more then likely this set may be able to function without the doorknob ? The crt does have factory dag and has a ground tab and the crt is aluminized with the ion trap really bright. Well I changed the Micas which were way off in value and the horiz is cured but had a line in the middle top to bottom which was with the new Micas it changed the horiz frequency and the hv was to high, adjusted , done. Then again the doorknob would have to be there because I think it provides focus voltage.

[timmy]

Ok now more trouble I have 4 mica caps 3 are rated 2500 volts and one rated 1500 volts, where the hell am I going to find those caps. I think the only ones made are 300 and 500 volts.

[Yamamaya42]

Originally Posted by timmy

Ok now more trouble I have 4 mica caps 3 are rated 2500 volts and one rated 1500 volts, where the hell am I going to find those caps. I think the only ones made are 300 and 500 volts.

what uf value?

[Yamamaya42]

598-CDV30FK302J03 $20 each?

[timmy]

2 - 10 pf and 1- 22pf and 1-5 pf the 22pf is 1500 volts the others are 2500 volts.

[Yamamaya42]

that's really high , you may have to go film, for lack of being able to find anything else :/

[Electronic M]

Originally Posted by Yamamaya42

that's really high , you may have to go film, for lack of being able to find anything else :/

Those cap values are pF so really low...

If micas are not available C0G ceramic caps would be a viable alternative.

[timmy]

Originally Posted by Electronic M

Those cap values are pF so really low...

If micas are not available C0G ceramic caps would be a viable alternative .

cog ?

[Electronic M]

C zero G it is a temperature coeficent rating for ceramic caps...that specific rating means they don't drift with temperature changes....old ceramics were hard to make temperature stable so micas were used instead.

[Yamamaya42]

Originally Posted by timmy

cog ?

https://www.allaboutcircuits.com/tec...pacitor-types/

[timmy]

Oh ok I should have know, npo marked on some ceramics the temperature stability. Ok I just have to find them now. I can get my hands on 12pf to take the place of the 10pf caps would this make much difference ?

[old_tv_nut]

Originally Posted by timmy

Oh ok I should have know, npo marked on some ceramics the temperature stability. Ok I just have to find them now. I can get my hands on 12pf to take the place of the 10pf caps would this make much difference ?

Where in the circuit is the 10pF cap? This will determine if the value is critical.

[timmy]

It's in the horizontal but I don't think it's in the oscillator since I just changed 3 Micas in the horiz multi. The 2 10pf caps one comes off the horiz drive adjustment to the flyback along with a 5pf in series and the other 10 is across 2 680k resistors to one side of the vert output transformer. And ties to one part of the yoke.

[old_tv_nut]

Well, the schematic image that was posted is almost too fuzzy to read, but if I am reading it right, the 10 pf is the one on the right and the 5 pf is in series to the left and then goes to the horiz drive adjustment variable cap. I can't make out the range of the variable cap, but I suspect it's great enough to handle a change from 3.33 pf to 3.53 pf, which is the series combo of 12 and 5 pf vs. 10 and 5 pf.

The 10 pf across two 680k resistors goes to a connection that goes off the page to the right, so not sure what it is doing or how critical. I guess you could try 12 pf, or you could put a 56 pf (or 68 pf) in series with 12 pf to bring the total closer to 10.