I am starting to recap a Hallicrafters 5R34A AM/ Shortwave radio from the early 1950's. One of the paper capacitors (0.05 MFD, 600 Volt) has a coil of wire wrapped around it. There are about 20 turns of wire, looks like 24 gauge or so, tightly wound. The capacitor appears to be an original one from the radio manufacturer and the coil seems to have been installed at the factory (wax covers both the capacitor and the coil).

What is this coil for, and do I need to replace the coil if a replacement capacitor is installed?

Thanks for your comments.

Hi Robert

The coil around a cap makes a tuned circuit. It was supposed to prevent a type of interference from stations below the broadcast band. Signals are no longer there.

You can replace the cap with a .047 mf and leave off the coil.

Norm

:I am starting to recap a Hallicrafters 5R34A AM/ Shortwave radio from the early 1950's. One of the paper capacitors (0.05 MFD, 600 Volt) has a coil of wire wrapped around it. There are about 20 turns of wire, looks like 24 gauge or so, tightly wound. The capacitor appears to be an original one from the radio manufacturer and the coil seems to have been installed at the factory (wax covers both the capacitor and the coil).
:
:What is this coil for, and do I need to replace the coil if a replacement capacitor is installed?
:
:Thanks for your comments.

:Hi Robert
:
: The coil around a cap makes a tuned circuit. It was supposed to prevent a type of interference from stations below the broadcast band. Signals are no longer there.
:
: You can replace the cap with a .047 mf and leave off the coil.

Norm, you are right and wrong, too. The stations are still below the broadcast band, but they are very low power now. My airplane had an ADF (automatic direction finder) but it is more interesting to listen to a radio station in the broadcast band that has news and music, rather than Morse code indentifier beeping three letters every five seconds. We have a 50kW station here in Atlanta, WSB, I have followed that all the way from Jacksonville. Just keep the needle pointing straight up, and land when you cross I-20
Lewis

I recently recapped a Philco 40-120 and cap/choke '8' had a few turns of solid wire on it. Put a few turns on the replacement cap as well and am curious if this is present for the same reason of filtering. Looks like it is in the RF section too.

http://www.nostalgiaair.org/PagesByModel/321/M0013321.pdf

:Hi Robert
:
: The coil around a cap makes a tuned circuit. It was supposed to prevent a type of interference from stations below the broadcast band. Signals are no longer there.
:
: You can replace the cap with a .047 mf and leave off the coil.
:
:Norm
:
::I am starting to recap a Hallicrafters 5R34A AM/ Shortwave radio from the early 1950's. One of the paper capacitors (0.05 MFD, 600 Volt) has a coil of wire wrapped around it. There are about 20 turns of wire, looks like 24 gauge or so, tightly wound. The capacitor appears to be an original one from the radio manufacturer and the coil seems to have been installed at the factory (wax covers both the capacitor and the coil).
::
::What is this coil for, and do I need to replace the coil if a replacement capacitor is installed?
::
::Thanks for your comments.

Tony - yes, that #8 thingamabob is there to shunt coastal maritime stations below the BC band. I think some Zeniths had a trimmer to fine-tune the filter.
Doug

:I recently recapped a Philco 40-120 and cap/choke '8' had a few turns of solid wire on it. Put a few turns on the replacement cap as well and am curious if this is present for the same reason of filtering. Looks like it is in the RF section too.
:
:http://www.nostalgiaair.org/PagesByModel/321/M0013321.pdf
:
::Hi Robert
::
:: The coil around a cap makes a tuned circuit. It was supposed to prevent a type of interference from stations below the broadcast band. Signals are no longer there.
::
:: You can replace the cap with a .047 mf and leave off the coil.
::
::Norm
::
:::I am starting to recap a Hallicrafters 5R34A AM/ Shortwave radio from the early 1950's. One of the paper capacitors (0.05 MFD, 600 Volt) has a coil of wire wrapped around it. There are about 20 turns of wire, looks like 24 gauge or so, tightly wound. The capacitor appears to be an original one from the radio manufacturer and the coil seems to have been installed at the factory (wax covers both the capacitor and the coil).
:::
:::What is this coil for, and do I need to replace the coil if a replacement capacitor is installed?
:::
:::Thanks for your comments.

I'm not positive, but it seems like those strong maritime stations, or a harmonic thereof, could jump into a receiver's IF section. Or maybe it was an image issue?
Doug

:Tony - yes, that #8 thingamabob is there to shunt coastal maritime stations below the BC band. I think some Zeniths had a trimmer to fine-tune the filter.
:Doug
:

Thanks, Norm, and everyone. I was not looking forward to trying to wrap wire around a tiny modern capacitor.

Robert

:Hi Robert
:
: The coil around a cap makes a tuned circuit. It was supposed to prevent a type of interference from stations below the broadcast band. Signals are no longer there.
:
: You can replace the cap with a .047 mf and leave off the coil.
:
:Norm