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Polyester film capacitors

I found 4 of those grey scavenged caps, 1uF only, and they all checked good and close tolerance (lowest 0.997 and highest 1.037 uF)

Also checked as a coupling cap between sig gen output and measering input of my hp8903b using several frequencies to see if there was distortion. I see a small difference between a cap and a short but this is the very same testing other caps.
 
As for film caps as a whole, other than certain ones used a long time ago in tube gear, the only ones that tested out of spec for me were one of those gray caps, and some black polypropylene caps with red ends used in some speaker crossovers.
The only reason I even tested the gray ones to begin with was because of a few posts I read about some being found to have drifted. Film caps usually last a very long time, butt there are known bad brands. Including mine and the OP's findings along with a few others, I was inclined to just replace them when found.
 
gslikker said:
Btw I think the "crystal radio" , when making one now, would receive LED power supply and other RF rubbish mostly.
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gslikker said:
Dunno, I tried making one but I had the luxury of having a germanium diode, so having this esoteric piece it does not count.
It is how most extremists started and if it ends up tinkering audio stuff it is pretty harmless.:rflmao:
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Agreed. Kinda takes the crystal out of crystal radio. Being able to see and touch the actual crystal and catwisker was part of the DIY experience. My mother recalled how "Pop had to adjust the catwisker" to get best reception, about a hundred years ago.
 
gslikker said:
Btw I think the "crystal radio" , when making one now, would receive LED power supply and other RF rubbish mostly.
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Yeah. Now it's rechargeable in a 2x2mm IC with built-in 10W nanospeaker and bluetooth of course, range 100Khz to 10Ghz--from China. Doesn't even come with headphones.
 
gadget73 said:
not sure the foil thickness would really affect it so much, but the thickness and quality of the wax paper would. If you wanted to go nuts you could experiment with different types of paper, plain, waxed, oil dipped, etc to tune the sound of your AM detector.

if you really want to go "foxhole" style, a rusty razor blade also works as a detector
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  • Like Thomas Edison experiments with filament materials, huh, to invent a practical electric lightbulb--over 6,000 different types tested.
  • At the scientist level, it's interesting how an RF signal flows from "aerial" (horizonal antenna) through the circuit to produce audio in headphones.
  • Very interesting about the razor blade; I believe that would be a "detector" then, though not a crystal type, acting as a rectifier of the received AC radio signal.
  • Urban legend reports that when dentistry filled cavities with metallic filling (I guess like amalgum) there were rare cases of a person picking up radio transmissions (like AM stations) that they could actually hear. Trace that RF signal!
 
Lavane said:
Those flat gray caps are known to be bad caps. I've run into the same thing with a couple model 140 power amps. Even if they are still within spec, they effect the sound, and not in a good way. Just replace them with a polypropylene film cap. In one of the 140's I replaced them with poly caps since one was out of spec. They were still within spec in the other 140. After restoring both with the same components, I did an A/B test between them. The amp with the polyester caps sounded kind of sterile compared to the other. I just replace those flat grays now when I run across them.
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  • Good to learn more about capacitors, appreciate the shared knowledge.
  • I got a little transient here I know, with the crystal radio stuff, sorry if it strayed from capacitor subjectmatter. I don't want to act in that capacity.:D
 
I will add one other thing, the gray cap I found that was off, came out of a like new 140 power amp that had been returned to the dealer. Apparently it never got sent back for repair. The store's stamp and address were on the outer shipping box, the sales box was inside. The amp came to me in the factory packaging and all literature. It was pristine. What I found was the meter lights didn't work. So I'm guess that's why it was returned originally. I found the wiring for the meter bulbs had never been soldered in. So this was pretty much a brand new amp with a bad film cap.
I still have the amplifier.
 
Lol, down Mexico way the "just over the border" stations broadcasting AM at 100k watts and up (no FCC regs over there, eh?) could make the fences play. Literally.

A point contact between two fillings would indeed work just fine as an AM radio.....
 
HPMguy said:
Lol, down Mexico way the "just over the border" stations broadcasting AM at 100k watts and up (no FCC regs over there, eh?) could make the fences play. Literally.

A point contact between two fillings would indeed work just fine as an AM radio.....
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  • Essentially a detector-in-a-tooth somehow, I'm told. I think Maxwell Smart had a more sophisticated one, a transceiver; probably "bluetoothed" to shoe phone.
  • Too lazy to look it up right now but yes, one of those mex stations in particular is legendary (broadcasting early country music all over), across from Del Rio I believe. It's a fact that the antenna and nearby fencing were so energized they emitted a blue corona. Never heard about the fences themselves actually producing audio :dunno: but anything's possible. Gets down to rf electomagnetic power density and its effects, like EMP bomb/nuc or lightning. For example, during an impending severe thunderstorm--air was kinda yellow-ish outside--my mother's set of keys lying on the kitchen table "sparked", no big lightning strike/thunder or anything just then, either. Induction, or psychic phenonoma?:eek: Anyway, all fascinating cool stuff!
 
A tight fence would actually work like a speaker down in Texas, it's an old country music joke. Pretty annoying if you don't like what they are playing.
 
My fathers HAM radio would come through a portable cassette tape machine's speaker that belonged to a kid next door. It scared the kid every time until one day the kid was telling me about his haunted cassette player, and I explained it was probably my father's transmitter.
 
There was an excellent Gilligans Isle where I believe they reverse engineered Gilligan’s mouth (fillings) to act as a transmitter so they could get rescued. Thankfully it didn’t work. Now what’s this about film caps?
 
knifeswitch said:
There was an excellent Gilligans Isle where I believe they reverse engineered Gilligan’s mouth (fillings) to act as a transmitter so they could get rescued. Thankfully it didn’t work. Now what’s this about film caps?
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  • Yeah, the Professor was quite the techno-weenie genius; also amazing how he could focus on fantastic inventions what with Ginger and MaryAnn around...they were quite a pair.
  • I must've missed the Gilligan's fillings episode but wasn't there another one where he made a parabolic dish antenna from a coconut shell and blue-thoothed it? Pair that.:naughty:
 
drjim said:
It's called the "Rusty Bolt Effect"...
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Thanks for another solid reference, right down to the complex mathematics.
  • I understand that here we're talking about RF phenomena but it also reminded me of galvanic fretting corrosion such as with rivets in a bridge: sometimes little differences between the steel alloy in a beam and the rivet produce an electrolysis effect between dissimilar metals which can eventually eat away enough metal to cause structural failure. Fretting corrosion on electrical contacts caused six+ F-16 crashes before discovered. It's always somethin', and Mr. Murphy is always waiting.
  • Awhile back a Collins engineer designing the advanced avionics for a next-gen airliner told me they figure there's usually about a million discreet rf signals in the air, from all kinds of sources. (In the specs for a good radio receiver you see "sensitivity" and "selectivity", two things that affect its ability to "pull in" the one signal you want out of all the noise--but I digress.) I guess the more we discover about the universe it seems everything is interrelated one way or another.
 
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