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Mica question - Printable Version

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Mica question - MissouriLarry - 02-23-2026

I have only been tinkering around with learning tube radios for a year now.  I do have my first radio up and running but now I am working on another one.  I found what I believe is a bad mica capacitor. I am not a book smart kind of person, I learn by doing. The schematics are still very difficult for me to follow so I am having trouble figuring out what are the values.  On a webpage I found where one can enter the colors and it will tell you what the value is.  Mine has 4 dots that I can see but the only selections was 3, 4 or 6 dots.  I entered the 3 that are in a row and it came back as 50,000pF.  Can someone help me and maybe explain how to id this?  I have been purchasing my parts from Tony's but where can I get these and what do I need?

RE: Mica question - radiorich - 02-23-2026

Hello Larry,
Well it's hard to see in that photo but if that part Says micamold on it that is not mica cap but a paper cap in bakelite type material !
Sincerely Richard

RE: Mica question - MissouriLarry - 02-23-2026

RadioRich,
That is exactly what it says. I need to find a suitable replacement, the back if it is all burnt out.

RE: Mica question - MrFixr55 - 02-23-2026

Hi Larry,

Where is the capacitor on the schematic? Or what pins on what tubes does it connect to? What make, mode of radio? You state that the back is burned. Has the cap split open? Is this cap across the power line? More photos may help. Move the cap around if possible so as to get a good view as to what it connects to.

Congrats on completing your first radio and starting another, and welcome to the gang!!

RE: Mica question - morzh - 02-23-2026

Just to confuse you more: BTW Micamold that looks like this could also be a resistor.

RE: Mica question - radiorich - 02-24-2026

Hello mike,
Yes, I forgot about that so a schematic would be the best to locate the part .
Sincerely Richard

RE: Mica question - Arran - 02-24-2026

If you have an Ohmmeter try measuring across the ends, if it reads something close to 50,000 Ohms then it's more then likely a wire wound resistor inside, 50,000 MMF or PF is very unlikely for a mica cap, and Micamold paper caps are usually thicker then that.
Regards
Arran

RE: Mica question - RodB - 02-24-2026

Hi Larry, we're lucky MicaMold didn't make transistors. Can you picture one of these with 3 wires?
So, the color codes are confusing because at one time there were no standards for these because only a few manufacturers, or maybe one, made them. They just used what they wanted and some were intuitive. To be really sure you're seeing a cap or resistor it should be identified using the schematic. In the chassis, try to identify the parts or tube terminal the part in question is connected to. Maybe it's close to a tube socket to get you in the vicinity. It helps to write a pictorial diagram of the connections on paper then compare the diagram to the schematic. If the schematic has a parts list, often it will give you a description like "wirewound" or "mica". I'm thinking that this is a resistor because you said it is burnt.

RE: Mica question - MissouriLarry - 02-24-2026

RboB,
I appreciate your reply!  Once I get home tonight I am planning on doing some more investigating.  I do have the schematic but as I said in my first post, I am still learning how to read them.  That kind of information does not sink in quickly.  What ever it is, it is defiantly bad.  The back is all burnt out and there was black on the chassis.  I will get better photos.  I can't say if it is a resistor or a capacitor, I was leaning towards a paper cap.  I don't know.  If a cap the color code, from what I can find makes it a .05uf @ 400v.  Once I get some good photos of it installed I think I will remove it so I can get a good look and photo of it.

RE: Mica question - RodB - 02-24-2026

Well, it could be a power line filter cap. We don't see them used this way very often. MicaMold made paper caps like this, so maybe that is one of them. If so, replace it with a safety cap.