I would like to connect my Radio Shack mini amplifier to my 1920s one tube radio in place of the headphones. Would I connect the amplifier to the plate through a capacitor, and place a resistor from plate to B+ and negative lead of amplifier?

Hi Brian

That's the best way. Resistor between plate & B+ gives the output tube voltage. Capacitor between plate and amplifier input isolates DC from your amplifier.

Not knowing the exact circuit try 4.7K @ 2 watts for the resistor and .1 mf for a coupling cap.

Norm

:I would like to connect my Radio Shack mini amplifier to my 1920s one tube radio in place of the headphones. Would I connect the amplifier to the plate through a capacitor, and place a resistor from plate to B+ and negative lead of amplifier?
:

:I would like to connect my Radio Shack mini amplifier to my 1920s one tube radio in place of the headphones. Would I connect the amplifier to the plate through a capacitor, and place a resistor from plate to B+ and negative lead of amplifier?
:
Lewis

Lewis - would that be a more modern speaker to connect as an external output?

::I would like to connect my Radio Shack mini amplifier to my 1920s one tube radio in place of the headphones. Would I connect the amplifier to the plate through a capacitor, and place a resistor from plate to B+ and negative lead of amplifier?
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:I would need a schematic of the one-tube radio to be sure, but I think you're on the right track if the B+ for the tube plate goes through the headphones. Just measure the DC resistance of the phones for the resistor value, and use a, oh, say 200 Volt cap for the coupling. Get a decent speaker. If your amplifier is like mine, it will sound pretty good if you use a decent speaker.
:Lewis
:

:Lewis - would that be a more modern speaker to connect as an external output?

Brian:
My Radio Shack amp has an amp out jack, 1/8 inch phone plug. A larger speaker can be plugged into here and the sound is tremendousally
(if that's a word) better. My shop speake is a 6" speaker in a wooden box, with a 1/8 plug on the end of a plain piece of minature zip cord.
Sounds better than the little speaker Radio Shack provides with the amp.
Lewis

:I would like to connect my Radio Shack mini amplifier to my 1920s one tube radio in place of the headphones. Would I connect the amplifier to the plate through a capacitor, and place a resistor from plate to B+ and negative lead of amplifier?
:::
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::
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::I would need a schematic of the one-tube radio to be sure, but I think you're on the right track if the B+ for the tube plate goes through the headphones. Just measure the DC resistance of the phones for the resistor value, and use a, oh, say 200 Volt cap for the coupling. Get a decent speaker. If your amplifier is like mine, it will sound pretty good if you use a decent speaker.
::Lewis
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:

You might consider an RF isolation choke in the plate circuit, before the resistor and audio capacitor. Sometimes not isolating the RF can lead to the amplifier and its lead-in wires causing changes in regeneration, etc.

Another consideration would be an RF bypass capacitor (between .0005 and .001 MFD, approximately) from the plate circuit to B-. If the radio is regenerative, and there is a tickler coil in the plate circuit, the capacitor would be placed on the B+ side of the coil. This is also where the RF choke would be placed.

Try these if you have trouble, or if you just want to experiment. There may or may not be notable improvement in performance.

T.