[Arran]

I did not think that noting an "outside foil" would make any difference, mainly because poly-film caps don't really have a foil, it's a metallic deposit on two sides of a strip of plastic film. Even on the old style paper caps the manufacturers themselves didn't pay any attention to it, and those actually do have two strips of foil in them. I believe the section of the radio where this may have made a difference was in the audio section, but there they are basically passing AC, and blocking DC, but that would show up as a hum in the audio. The test I have seen in some videos was to connect a cap to a scope probe whilst holding onto the body of the cap, the trouble with this is that your body is acting as a wide band antenna, and your fingers are coupling directly to the outside of the cap, this is like grabbing the loop antenna of your radio with your fingers, the stations often get louder, if the caps are routed properly then they shouldn't have anything coupling to them other then what they are connected to.
The problem with the CL 90 is that it is too large, the 90 stands for 90 volts, so there is a 90 volt drop when they are cold, giving the tubes a chance to heat up. I've normally heard of people using these in series string TV's with a tube chassis, but those often have multiple strings of tubes in series, and they can be 300-400 ma in each string, and apparently they were not intended to work with loads under 500 ma. The string of your Stromberg is 150 ma, plus whatever the B+ is, so maybe 250 ma max. I do not think this has anything to do with the squeal, or lack of gain, I would suspect an open or drifted silver mica cap in one or more of the IF cans, this is a more common problem then the SMD/silver migration one.
Regards
Arran
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