Philco Model 20 - Printable Version
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RE: Philco Model 20 - Phlogiston - 05-26-2013
Yep, I used NP 630V caps in mine. They cost a lot more than electrolytics, but at 1.5mf, they are still cheap. Big ones over 10mf are $6 or $7 each.
http://philcoradio.com/phorum/showthread.php?tid=6731
RE: Philco Model 20 - pete7189 - 05-26-2013
These sets also use "bakelite block" caps, too.
RE: Philco Model 20 - Phlogiston - 05-26-2013
Yes, and there are 2 other metal cans besides the big one.
RE: Philco Model 20 - morzh - 05-26-2013
Yes, but they are a snap to restuff: they are not potted inside. You open them by straightening the tabs and the cap pulls out readily.
RE: Philco Model 20 - pete7189 - 05-27-2013
The same type of cap can be used in those as well?
RE: Philco Model 20 - Phlogiston - 05-27-2013
Well, yes, 630 Volt non-polarized of the correct value.
Keep in mind that, as I said in the thread above, most of the resistors are going to be bad as well. With the type used in that radio, they don't just drift off, they go open.
RE: Philco Model 20 - morzh - 05-27-2013
Pete
For these purposes any type of cap can be used. At these frequencies the caps behave very close to ideal cap and the currents are small.
Say, in today's digital devices or in a switching power block there's no way you could take an electrolytic cap, solder it to wires 6" long and be siccessful. In the old radios this is OK to do.
So as long as your cap meets the voltage/capacitance requirements it is OK to use.
In case of electrolytics you have to watch your polarity.
One notable exception is RF filter caps; they need to have a very good thermal drift coefficient and need to be soldered using short leads. This is why mica caps were used there; today you can use either those or NPO/C0G dielectric type ceramics.
For all your other major needs (sorry for the pun) except where the electrolhytics use is warranted due to high capacitance (there is no other reason to use them) polyester film caps will do just fine.
RE: Philco Model 20 - GarySP - 05-27-2013
I used polyfilm caps for everything. The bakelite bypass caps aren't very hard to rebuild, just be gentle with them so you don't break them. Lots of info in the website on how to restuff them. One has resistor wire in it as well. I used a 250 ohm half-watt resistor there. Take care. Gary
RE: Philco Model 20 - morzh - 05-27-2013
Rebuilding a backelite takes me some 10-15 minutes, and I am taking my sweet time; rebuillding an electrolytic takes me a minimum of 1hr. You have to desolder it, cut part of it off, gut it, clean it, fit the new caps in, possibly drill some holes, pot it, glue it back together, solder it back.
A backelite - just unscrew it, no desoldering, gently heat it,, push the guts out, put the new cap in, solder it, screw it back. A snap.
RE: Philco Model 20 - pete7189 - 05-28-2013
Will mylar caps work as good as poly film?
RE: Philco Model 20 - Radioroslyn - 05-28-2013
Yup
Terry
RE: Philco Model 20 - klondike98 - 05-28-2013
Morzh, why do you pot the restuffed condenser can? I've cut the can, gutted it, drilled the holes for cap leads and then used a thin strip of electrical tape to hold the two parts of the can together before clamping the can into the mounting bracket. That seems to hold things pretty well, the tape is not visible since its under the clamp and I can easily undo it all if the cap should need replacing or, heaven forbid, I screwed up the restuffing in the first place. what am I missing here? Thanks!
RE: Philco Model 20 - morzh - 05-28-2013
No reason other than it will old a cap on its thin leads from sagging and shorting to something. If the leads are short and stubby and he cap is small ... no real need.
Just something I am mentally comfortable with.
RE: Philco Model 20 - klondike98 - 05-28-2013
Ah..thanks, hadn't thought about sagging although I do insulate the leads.
RE: Philco Model 20 - pete7189 - 06-01-2013
When I had the chassis out of the cabinet today, I noticed some past repairman bridged an electrolytic across one of the ones on that large can. I don't recall seeing that electrolytic on the schematic. Next time I have it out, I'll take a pic and post it on here.