When is it a bad idea to use ceramic capacitors?

[benman94]

Hey Guys,

Just wondering, when is it a bad idea to use a ceramic capacitor in a set. I'm nearing the end of my first TV recapping and have only a 1000 volt tubular paper vertical discharge capacitor left to replace. Would it be ok to use a ceramic disc capacitor here? I have one on hand...

Thanks!

[Eric H]

Vertical is probably the worst place to use Ceramics, you will probably have linearity problems if you use it there.

[Phil Nelson]

I avoid using ceramics in vertical and horizontal sweep circuits in general, as Eric noted.

If you don't have the needed value in 1000-volt caps, you can combine two 630-volt caps in series to make one cap with half the capacitance and twice the voltage rating.

For instance, say that you need a .1mfd/1000v cap. Wiring two .22mfd/630v caps in series gives you a .11mfd/1260v cap. That should work for the time being and allow you to progress in your restoration, while you order the 1000v cap you need.

Phil Nelson

[benman94]

Glad I've been using polyester caps then. So would it be wise to just avoid ceramics all together?

[Eric H]

Originally Posted by benman94

Glad I've been using polyester caps then. So would it be wise to just avoid ceramics all together?

Generally speaking, yes.
I have used them in the Horizontal circuit of some 7" Electrostatic sets with no problem but I know they won't function properly in the Vertical circuit of the same sets, something to do with the frequency capabilities or so I was told.

[wa2ise]

Ceramic caps are fine for RF bypass duty, you see them in tuners, IF strips and sound IFs. They rarely go bad, so you shouldn't need to replace those. You usually avoid using ceramic caps in any tuned circuit (though some specially made ceramic caps, made to not drift much over temperature, are found in RF circuits, they are usually 5 to 100pF range). And avoid using ceramic caps in RC oscillators, like vertical osc circuits. Or horizontal oscilators, where the cap is part of the timing circuit.

Audiophiles avoid ceramic caps in audio amplifiers for hifi work, but if the amp in question is the usual 1 watt tube driving a 4 inch speaker in the side of the TV cabinet, ceramics will work well enough

[Einar72]

So what was the characteristic of the capacitor elements used in those ceramic-plate vertical integrators that were once so popular in Zenith TV's?

[DavGoodlin]

Originally Posted by Einar72

So what was the characteristic of the capacitor elements used in those ceramic-plate vertical integrators that were once so popular in Zenith TV's?

Good question. My '62 Motorola BW has one called a "vertical integrator", an integrated RC network intended to reduce assembly costs.

Are these are also called "gimmicks" in the audio stages of many tube radios?

[old_coot88]

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[old_coot88]

Originally Posted by DavGoodlin

Good question. My '62 Motorola BW has one called a "vertical integrator", an integrated RC network intended to reduce assembly costs.

Those were generally called 'couplates'.

Are these are also called "gimmicks" in the audio stages of many tube radios?

Um.. a 'gimmick' usually referred to a very small value capacitor (2 - 3 pf or so) consisting of pair of insulated wires twisted together for a few turns. Sometimes used for neutralizing an RF or IF stage prone to oscillation.

[DavGoodlin]

Gimmicks, ah yes.
I saw those in Zeniths IIRC, except they were just 1/2" long parallel pieces of enameled copper wire, not twisted.

[Einar72]

I once saw the term "bulplate" to describe them. Everything from my AA6 Silvertone clock-radio to my Philco-built '67 Cougar radio used 'em.

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