'MicaMold' capacitors - UK Vintage Radio Repair and Restoration Discussion Forum

Skywave · 25th Oct 2019, 10:58 pm

'MicaMould' capacitors: I'm sure many of us have seen them. They're usually in big metal cases, chassis mount, non-polarised, often with screw connections. Capacitances are typically 1 to 20 uF; working voltages can typically range from 300 to 1500 v.d.c.; similar for a.c. voltage ratings.

So question: is there any demand for these capacitors these days? I have a large quantity (various C and V) that I doubt I'll ever use.

Al.

Argus25 · 25th Oct 2019, 11:15 pm

I think there could still be some demand for them. I have found that these physically larger high voltage types are much more reliable than their smaller molded counterparts, less often short out. Mostly these types of caps were deployed as RF bypasses or antenna coupling capacitors etc. They could still be of use to those interested in making high voltage power supplies, like the Tesla coil enthusiasts.

Silicon · 26th Oct 2019, 12:43 pm

The Micamold capacitors that I have encountered are the paper insulated ones encased in a molded bakelite case.

They are leaky and best replaced if you want a working radio. Fine for a museum.

Maarten · 26th Oct 2019, 1:16 pm

Micamold up to a few nF are really mica, larger ones are all paper as far as I know. I've never heard of ones in metal cans. Those might be slightly more reliable, though you might not want to depend on them where failure can cause damage.

GMB · 26th Oct 2019, 2:16 pm

My understanding is that this type of capacitor were meant to be substitutes for mica capacitors. Their origin is the USA during WW2 when there was a shortage of mica.

I do not know what they are made of but they behave like paper because they are invariably leaky. So maybe they are (usually) low value paper capacitors where the paper stood in for mica.

AC/HL · 26th Oct 2019, 3:32 pm

According to a post here: https://www.antiqueradios.com/forums...ic.php?t=34265
the smaller ones may be mica, but the larger ones are paper, and therefore suspect.
It's a brand rather than a technology.

GMB · 26th Oct 2019, 3:59 pm

My information is based on their actual advert of the period (but I can't remember where I saw it). They explained how they were saving precious US mica resources by making these substitute capacitors. I think the brand was created for this purpose - but may have lived on after the war.

25th Oct 2019, 10:58 pm	#1
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	'MicaMold' capacitors 'MicaMould' capacitors: I'm sure many of us have seen them. They're usually in big metal cases, chassis mount, non-polarised, often with screw connections. Capacitances are typically 1 to 20 uF; working voltages can typically range from 300 to 1500 v.d.c.; similar for a.c. voltage ratings. So question: is there any demand for these capacitors these days? I have a large quantity (various C and V) that I doubt I'll ever use. Al.

25th Oct 2019, 11:15 pm	#2
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: 'MicaMould' capacitors I think there could still be some demand for them. I have found that these physically larger high voltage types are much more reliable than their smaller molded counterparts, less often short out. Mostly these types of caps were deployed as RF bypasses or antenna coupling capacitors etc. They could still be of use to those interested in making high voltage power supplies, like the Tesla coil enthusiasts.

26th Oct 2019, 12:43 pm	#3
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	Re: 'MicaMould' capacitors The Micamold capacitors that I have encountered are the paper insulated ones encased in a molded bakelite case. They are leaky and best replaced if you want a working radio. Fine for a museum.

26th Oct 2019, 1:16 pm	#4
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,199	Re: 'MicaMould' capacitors Micamold up to a few nF are really mica, larger ones are all paper as far as I know. I've never heard of ones in metal cans. Those might be slightly more reliable, though you might not want to depend on them where failure can cause damage.

26th Oct 2019, 2:16 pm	#5
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,095	Re: 'MicaMould' capacitors My understanding is that this type of capacitor were meant to be substitutes for mica capacitors. Their origin is the USA during WW2 when there was a shortage of mica. I do not know what they are made of but they behave like paper because they are invariably leaky. So maybe they are (usually) low value paper capacitors where the paper stood in for mica.

26th Oct 2019, 3:32 pm	#6
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: 'MicaMold' capacitors According to a post here: https://www.antiqueradios.com/forums...ic.php?t=34265 the smaller ones may be mica, but the larger ones are paper, and therefore suspect. It's a brand rather than a technology.

26th Oct 2019, 3:59 pm	#7
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,095	Re: 'MicaMold' capacitors My information is based on their actual advert of the period (but I can't remember where I saw it). They explained how they were saving precious US mica resources by making these substitute capacitors. I think the brand was created for this purpose - but may have lived on after the war.