Capacitor substitute - Printable Version

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+--- Thread: Capacitor substitute (/showthread.php?tid=22234)

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Capacitor substitute - bgorman - 02-28-2021

Hey all
I'm working on a Philco model 201X. It has a Bakelite condenser #97 (one of many) on the schematic (attached). It houses 2  .0001 caps. When I compiled a list to order, I wrote this one down wrong and now don't have the right value in a film cap. I do have one in a Silver Mica, though. Was wondering if I could use the micas in this part of the circuit?
Bob

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RE: Capacitor substitute - radiodale - 02-28-2021

Silver mica is fine.

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RE: Capacitor substitute - Arran - 03-01-2021

You probably don't need to use silver mica, very likely a ceramic or film cap would be fine, but use what you have. I don't think that the caps they used in Bakelite blocks were that critical.
Regards
Arran

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RE: Capacitor substitute - mikethedruid - 03-01-2021

Be careful of the VOLTAGE you use in the blocks. For the caps in the AC input block use safety caps, X1 Y2, or Y2 250 Volt. If they ever fail they are designed to fail OPEN and not short, keeping the line voltage off the chassis. As for the other caps in the bakelite blocks I suggest you order the yellow 630 volt axial poly caps. They fit well, and are high enough voltage for all of these blocks. I use the yellow poly caps when replacing any of the old paper condensers also. I just order at least 10 of each commonly used value, and keep them on hand. I know I will use them eventually. If you don't plan to restore more than this one radio, just order for it. Look for all the paper caps in the set, both discrete and in the blocks, and order them all at once.

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RE: Capacitor substitute - bgorman - 03-02-2021

Thank you Dale, Arran & Mike
The only reason I'm not ordering the poly films is that I just placed 2 orders for this radio and the next one from Dave at Just Radios, but of course he has a min order (understandable) and I just don't need anything else to justify another order at the moment. So was hoping what I had would work. 

Arran, I would use a ceramic but don't have one. the only ones I have in 100pf are Micas. While I have a basic knowledge of tube circuitry, I'm still learning about which caps work best in the different parts of the circuit. I know from other posts, that the stability of the Micas are best in the RF sections, but wasn't sure if they would be a good fit where these are.

Mike, thanks for the reminder about the voltage, that is one thing I pay attention to. The micas I have are rated at 500v. I've been tempted as you say, to just order a variety of caps in bulk to have on hand, but just haven't pulled the trigger on it.  I did just as you suggested, went thru tallied up the caps to be replaced (films, Electrolytics & safetys) and ordered them, but when I was making my list forgot  a 0 for these. Wrote them down as .001 instead of .0001. I did order the line to ground safety caps you mention. I do understand the importance of those as well as adding a fuse on the hot side of the ac in, and using a polarized plug. I like the replica acorn style. 

Not sure if there is another post where the use of the different capacitors is discussed, but there has to be a reason why they went thru the trouble of making a Bakelite container, putting the caps inside, then filling them with a Plastic/Tar substance versus using a wax/paper cap. This radio also uses a rectangular "metal" container underneath, with caps and the Plastic/Tar stuffing as well. Does the Bakelite verses Metal containers serve different purposes, and is the purpose of the filler stuff to keep moisture out ?? 

"I love the smell of solder in the morning" well, actually at night.

Bob

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