View Full Version : should Ceramic Disc Caps. Be Replaced?


drillher
07-04-2010, 05:44 AM
I know that the old electrolytics and coupling caps should be replaced in a 40 plus yr. old amp.,but am wondering if the few ceramic discs should go also.Thanks,
Dave

battradio
07-04-2010, 06:19 AM
Any ceramic disc in the audio path should be replaced with a poly cap and the ones on the AC line should be replaced with a safety cap .

http://www.justradios.com/safetytips.html

Big Bill
07-04-2010, 07:16 AM
I know that the old electrolytics and coupling caps should be replaced in a 40 plus yr. old amp.,but am wondering if the few ceramic discs should go also.Thanks,
Dave

Thanks for asking the question, as I was wondering the same thing. :yes:

mashaffer
07-04-2010, 08:03 AM
It should be pointed out that replacing the ceramics in the signal path is a matter of sound quality not of reliability or safety. The safety caps are, of course, a matter of safety.

mike

Andyman
07-04-2010, 08:10 AM
What's a safety cap??

sgmlaw
07-04-2010, 08:19 AM
I know that the old electrolytics and coupling caps should be replaced in a 40 plus yr. old amp.,but am wondering if the few ceramic discs should go also.Thanks,
Dave

Possibly. Ceramics are among the most durable of capacitors, and rarely if ever fail. Audio path ones can make some changes, which one may or may not like. Don't expect meaningful changes in ancillary circuits. But never change in an RF circuit unless necessary. And any in a suppressor application should only be replaced with those specially rated for mains service.

battradio
07-04-2010, 08:45 AM
What's a safety cap??

See URL

http://www.justradios.com/safetytips.html

Andyman
07-04-2010, 08:51 AM
Thanks!

drillher
07-04-2010, 09:44 AM
Good link.I have to liik at the schematic and decide if I need to replace any of the discs based on the article.

Fisherdude
07-04-2010, 10:52 AM
It should be pointed out that replacing the ceramics in the signal path is a matter of sound quality not of reliability or safety...

mike

Possibly. Ceramics are among the most durable of capacitors, and rarely if ever fail. Audio path ones can make some changes, which one may or may not like. Don't expect meaningful changes in ancillary circuits. But never change in an RF circuit unless necessary. And any in a suppressor application should only be replaced with those specially rated for mains service.

What they said.:thmbsp:

gearhound
07-04-2010, 11:05 AM
They were used as coupling caps in a lot of older audio tube gear.
As had been said before, they rarely fail.
Some people will NOT change them out, to keep the original sonic signature?
I replaced the ceramic coupling caps in my late 50's Bell2285 int. mono amp, with NOS Sprague 118P waxed paper/polyester capacitors.
To me at least, it was an improvement.

Steve

benb
07-04-2010, 01:21 PM
Cerramic caps are bad for several reasons - they have nonlinear characteristics, thus they add distortion, and they are MICROPHONIC! Depending on where they are in the circuit, you can tap on them with a pencil and hear something come out of the speaker. Some tubes are microphonic, either by a questionable design or a loose part inside.
They were used as coupling caps in a lot of older audio tube gear.
As had been said before, they rarely fail.
Some people will NOT change them out, to keep the original sonic signature?
I'm thinking perhaps to keep it as original as possible as a collector's item.

dshoaf
07-04-2010, 01:36 PM
Ceramic caps can, indeed, go bad. As evidence, I offer the attached service bulletin from McIntosh noting a problem with popping as the selector controls were used. This is dated November of 1965. Thank goodness materials engineering has come a long way since then.

BTW, the symptoms noted by Mac in this bulletin can be applied to many other brands of that era.

Sgmlaw and others are correct, however, that generally ceramic caps don't fail as much or as badly as others. Do heed the admonitions for RF circuits, however, as you can affect operating parameters of the circuits.

I won't go into the discussion about whether sonics are changed. Too many threads on that here already.:no:

If our OP is considering keeping the unit as a collectors item, here's what I recommend:

- Clean it up nicely. It should be pretty much as it came out of the box it was shipped in - the box, owners manual and accessories should be there, too.
- Put it on a closed shelf to minimize any dust collection. This is especially true in higher humidity areas. Dust collects moisture which will cause pitting if left too long. This is very true with chrome plated chassis.
- Wrap the power cord up much like it was shipped if you can.
- Do not power it on.
- Gaze at it lovingly.

Cheers,

David

gadget73
07-04-2010, 11:05 PM
Any time I've replaced ceramics in the audio path, the sound changed. Its all subjective of course, but I have not put any back in. I just feel that ceramics don't sound very good. I never change them in RF circuits though, mostly for the reasons stated but also simply because most of the time, they aren't bad.