In the S-40 which has a similar audio output but a permanentf6
magnet speaker, the field coil is replaced with a 1500 ohm resistor.
There is no spec given for the S-20 transformer in the handbook I have
but its probably the same as used in the S-20R and S-40 series for the
6F6 tube. Check the tube data sheet but its likely about 4500 ohms
primary impedance to speaker voice coil. Not very critical. Same
transformer can be used for 6V6 and some other tubes. Mounted on the
speaker frame. If you replace the speaker with a PM one replace the
field coil with a 1500 ohm about 5 Watt resistor and if the transformer
seems to be OK try to remount it on the new speaker frame or on the
chassis someplace.
I should ask first what is wrong with the audio? Is the speaker
damaged?
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On 8/29/2024 3:20 AM, Lynton wrote:
Hello everyone. I have two Hallicrafters S20¡¯s. One has had the audio
modified with a large choke (value??) and an output transformer. It
produces audio but not very well!
The second has the original field coil speaker (see photo), but no
audio. My question is are the resistance values of the field coil
speaker correct? The radio is in good original unmolested condition.
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
