Use 400 or 600 volt caps for all regardless of the voltage they have across them in the radio. Use 450 volt electrolytic filter capacitors. Leave the old ones mounted on the chassis, disconnect and add new ones underneath. New capacitors, although higher voltage than the original, will be much smaller.
It is nice to put the new capacitor inside the original container but it probably will not have an effect on the value. Just don't put a new bright orange cap on top the chassis where it can be seen.
Norm
: I have an old RCA model 121 radio that I would like to restore. I have a schematic which lists the values but not the working voltage. The capacitors are the old paper type. they do not have a value or working voltage on them. They only have a 5 digit code on them. Can anyone tell me what the codes stand for? I need to know the working voltages. What should I replace these capacitors with? I would like to keep the chasis as original as I can. I was hoping to hide the replacement capacitors inside the old cardboard tube. What are the guidelines for replacing the capacitors in antique radios? I do not want to decrease the value of the radio with my repairs.
If you want to place the new caps inside the old tube,
all you have to do is heat the old caps until you can
slide the inards out by tugging on the wire lead. My
method is to remove all the caps, marking their original locations as I go, suspend them by their leads over an old baking sheet and pop them in the oven at 350 for about 5 minutes, the tubes will usually slide right off on their own and all you have to do is clean off any excess wax on the outside of the tube.
2 warnings on this method - it smells bad, make sure
you have plenty of ventilation when doing it. I don't
think the fumes are toxic, but they don't smell good.
The other is, your wife probably won't be happy with you, luckily mine is pretty understanding. You could
do this with a hot plate or heat gun too.
Once removed put the new cap in and fill with melted
wax. You'll have to stuff one end of the tube with a
lille partially hardened wax so the molten stuff doesn't just run right through. Try to find wax the same color as the original. Those candle kits in a bag work great, I've found brown ones at places like Wal-Mart that match the original wax exactly.
Although the value of the radio probably isn't much
effected, it is more aestetically pleasing to keep
special radios looking original. You could even
age the new solder joints to look old. I saw some
postings on this on www.antiqueradios.com.
Can caps are more difficult to rebuild. I usually
just wire the new ones underneath. If the can has
a cardboard sleeve over it, you can remove that, cut
the metal portion off just above the base,(a Dremel
is handy for this) remove the wax, tar and foil and then replace the cardboard sleeve with a little hot glue to keep it attached to the base. Make sure you
have your new caps properly grounded.
Good luck with your restoration.