Silver mica capacitor replacement - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: August 15, 2021, 12:40:25 am
content: I have a bad 500pf 2kv silver mica Capacitor in a HF amplifier. The capacitor is the 80 meter RF padding capacitor. Now my question is I have 2ea CDV16FF102JO3F Capacitor Mica 1000PF 5% 1000V. I know using in series it will give me the 500pf 2kv I need but is Mica any different than silver mica?Would these be applicable to use?

author: ambrosia heart
author_rank: Regular Contributor
timestamp: August 15, 2021, 01:40:43 am
content: "Capacitor Mica 1000PF 5% 1000V. I know using in series it will give me the 500pf 2kv I need but is Mica any different than silver mica?"For audio you may hear a change of sound.For other parts, no problem due to capacitance andworking voltage OK.

author: bob91343
author_rank: Super Contributor
timestamp: August 15, 2021, 04:36:25 am
content: I am not sure I agree that two 1 kV capacitors in series will withstand 2 kV. Unless you add equalizing resistors.Silver mica is just a contruction method. The capacitors should work, as long as they don't break down. In addition, the RF current specification needs to be respected. This varies widely with different capacitors, so check that first.

author: bd139
author_rank: Super Contributor
timestamp: August 15, 2021, 08:40:08 am
content: The silver micas are pretty difficult to get hold of these days at high voltages. However there are now ceramic MLCCs that are C0G dielectrics that go up to 1000pF and 2000v.They do RF specific ones as well but those are more expensive.https://www.mouser.co.uk/datasheet/2/212/KEM_C1009_C0G_HV_SMD-1102723.pdf

author: Vovk_Z
author_rank: Super Contributor
timestamp: August 15, 2021, 04:17:15 pm
content: Quote from: bob91343 on August 15, 2021, 04:36:25 amWe use equalizing resistors with electrolyte caps, but not with any other type, usually. Because it'll degrade their performance much.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: August 15, 2021, 08:44:45 pm
content: no problem to get hold of Micas, Mouser has all kind of Mica by Cornell Dubilier, no problem thereif it's a matter of power & RF, the other viable choice are ATC caps

author: Jwillis
author_rank: Super Contributor
timestamp: August 16, 2021, 02:49:57 am
content: Mica capacitor is just casual reference to Silver Mica capacitor . Old style (pre 1930s) Clamp mica caps are obsolete because of poor stability and tolerance .Silver mica capacitors have a very low tolerance of around ±1% and have low resistive , inductive losses and have high Q-factor because of low thermal losses.So for HF applications they are not really interchangeable with ceramic capacitors .

author: rsjsouza
author_rank: Super Contributor
timestamp: August 16, 2021, 01:55:26 pm
content: If in the US, there are several surplus stores that sell Mica capacitors at a reduced price when compared to brand new ones. One of my current favourites isElectronic Surplus

author: MarkL
author_rank: Unknown
timestamp: August 16, 2021, 08:18:05 pm
content: Another source of mica capacitors (and a lot of other older electronic parts) is Surplus Sales of Nebraska:https://www.surplussales.com/They have a large selection and the site is well organized, but they tend to be more pricey.

author: radiolistener
author_rank: Super Contributor
timestamp: August 17, 2021, 09:43:56 am
content: Quote from: ambrosia heart on August 15, 2021, 01:40:43 amNo. For audio applications it doesn't matter if you replace silver mica with some ceramic capacitor. You cannot notice significant change. But for HF it is very important, because HF applications usually needs very high Q of the capacitor, otherwise they will have high losses and it will lead to heating and as result change capacitance (due to temperature coefficient) and you will need to tune your circuit. Due to the power loss, such replacement will reduce sensitivity or reduce power output of your circuit. For HF amplifier, replacing silver mica with some worse Q capacitor leads to overheating and even damage.Quote from: Crambone on August 15, 2021, 12:40:25 amif you're looking for silver mica replacement for HF applications, you can use porcelain multilayer high Q capacitors:https://eu.mouser.com/datasheet/2/40/100b-1920467.pdfhttps://datasheets.avx.com/100B.pdf