junk micas

[radio nut]

Originally Posted by Einar72

Don't spend yourself in a hole with all these caps - capacitor mfg. techniques today produce a product far more stable and long-lived than the old wax-dipped or molded-case paper caps. These modern caps are often far better than what was available (or used) in the 30's or 40's. If you can find micas in the reddish dip at tube voltages, go for it. But you are repairing old radios, not missile-guidance or heart-pacemaker devices. Just buy (as I stated previously) temp-stable ceramics for RF circuits if you can't find the value you need in mica. Unless you listen to single-sideband hams on the 20-meter band, you won't be bothered with drift issues.

I guess I am alittle confused here. Fair radio has new manufacter ceramics but how do I know that they are temp-stable? I am putting more effort into this set because it is my first FM set and its a capehart and high fidelity."Maybe" I am sweating the small stuff too much but in my area higher end sets just don't come up for sale often. I am just trying to "get it right" I have been working on radios for over a decade but this is the best radio ( and the most complex) I have come across.

[jaymanaa]

I guess I'm not done with my Zenith after all.

[Chad Hauris]

I have used ceramic on IF capacitor replacement in the past but now that I have been able to find new mica caps I use them. I have never had any trouble with ceramic though. 22 pf for FM circuits and 100 pf for AM circuits has always worked for me. I am seeing a lot more bad mica caps in IF's, probably 75% of the 50's-60's tube radios have these bad caps. The radio might start to work good when all other caps have been replaced but after a short while of playing bad mica caps began to show up, or too often you replace all other caps and there is no sound and it is bad caps in the IF cans. Hammarlund HQ-180 has been the most difficult to repair radio with the bad mica caps as there are so many IF stages.

[Einar72]

Easy rule for Ceramics: For RF work, ask for temperature coefficient NPO when buying older parts on eBay or C0G when buying new on Digi-Key, Mouser, Allied, et cetera... Yes, that's a zero between the C and G.