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In Reply to: RE: Metal film resistors in tuners? posted by Thermionic27609 on August 25, 2015 at 20:14:43
I have an article here somewhere which goes into this subject in some detail. It refers to all RF circuits, not just FM tuners. My take-away point from reading it was to replace carbon or carbon film resistors with similar replacements. The circuits were designed to work with those types, and there is a difference in the way resistors perform at radio frequencies.
In the power supply and audio section, metal films are OK, of course.
I'll try and find the article and I'll post it if I can locate it.
"You won't come back from Fletcher-Munson curve"-Jan and Dean
Follow Ups:
Here's the pertinent portion of the article, mainly the second and third paragraphs, which pertain to replacing resistors in radio frequency circuits.
I included the cover and author to show that both the article and magazine were geared toward guys who made a living repairing VCRs, CB radios, etc, not toward magic crystal tweakers.
After reading this article in 1996, I've always substituted like for like in tuners. If it had a carbon, I replace it with a carbon. If it had a carbon film, I replace it with a carbon film. I don't know enough about RF circuits to know when it would be acceptable to deviate from this path.
"You won't come back from Fletcher-Munson curve"-Jan and Dean
Specifically, carbon composition parts are both non-metallic and non-inductive. Carbon film parts are spiral trimmed, which introduces inductance. Small amounts of inductance MATTER at RF.
There is 1st hand experience of metal oxide parts, which can sound like guano, working well at RF. See the AVA article on FM-3 tuner care.
Eli D.
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