What kind of capacitors are these? - Page 1
Forum section: electronics / beginners

author: oPossum
author_rank: Super Contributor
timestamp: July 19, 2018, 04:13:40 am
content: These are in a Heathkit IN-27 decade capacitance box. They have a waxy feel. Looks like a single layer dielectric - not wound. SRC may be the manufacturer - Societe de Composants Record.What is the likely dielectric and plate material?

author: RJFreeman
author_rank: Regular Contributor
timestamp: July 19, 2018, 04:31:24 am
content: My guess would be Silver Mica Capacitors

author: +Mikie
author_rank: Contributor
timestamp: July 19, 2018, 11:20:51 am
content: My guess would be paper capacitors. If you're interested in replacing them use either ceramic, MKT or MKP.

author: Unknown
author_rank: Unknown
timestamp: July 19, 2018, 11:50:44 am
content: I'd say they were mica caps, they look like old micas. Being used in a substitution box they need to be accurate and stable. I seem to remember most of the paper caps were cylindrical and as reliable as a 2 week weather forcast.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 19, 2018, 01:46:29 pm
content: Quote from: RJFreeman on July 19, 2018, 04:31:24 amMine, too!Australian mica caps usually were coated with hard Bakelite, but those from the USA & UK often had that waxy encapsulation.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 19, 2018, 02:03:10 pm
content: silver mica!

author: David Hess
author_rank: Super Contributor
timestamp: July 19, 2018, 06:14:30 pm
content: The 1% tolerance, size, and form factor are enough to know that those are silver mica capacitors however in case there is any doubt, they were made by SRC (Stability Radio Components).

author: oPossum
author_rank: Super Contributor
timestamp: July 19, 2018, 08:25:20 pm
content: Wow. No doubt that is what they are. I have never seen this style of old cap before, and all the silver mica caps I have seen are the modern epoxy encapsulated style. Thanks to all who responded.Testing with a DE-5000 suggest they are still within spec.Code:103.7 +3.70%203.0 +1.50%302.9 +0.96%403.0 +0.75%503.7 +0.74%604.3 +0.72%703.4 +0.49%804.1 +0.51%904.7 +0.52%1004.7 +0.47%1.003 +0.30%2.009 +0.45%3.017 +0.57%4.006 +0.15%5.007 +0.14%6.015 +0.25%7.020 +0.29%8.021 +0.26%9.028 +0.31%10.026 +0.20%10.07 +0.70%20.12 +0.60%29.85 -0.50%39.75 -0.63%49.83 -0.34%59.87 -0.22%69.57 -0.61%79.69 -0.39%89.73 -0.30%99.79 -0.21%

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2018, 08:46:49 pm
content: QuoteDon't damage that soft wax coating (yes, it is wax) that keeps the moisture out and they should stay that way for alongtime. Stability is Silver Mica's forte.

author: +Mikie
author_rank: Contributor
timestamp: July 20, 2018, 12:34:38 am
content: Quote from: Z80 on July 19, 2018, 11:50:44 amYeah, my bad. Paper ones were always cilindrical, you could see the layers from the sides. It was fun unrolling them, that's about all they were good for

author: David Hess
author_rank: Super Contributor
timestamp: July 20, 2018, 01:47:03 am
content: Quote from: +Mikie on July 20, 2018, 12:34:38 amThey did make rectangular paper capacitors as shown at the first post here for M1 and M2:https://www.radiomuseum.org/forum/replacing_old_capacitors.htmlMy ESI impedance bridge uses mica capacitors are shown for M4 at the above link with the colored dots for the oscillator and filter.