Please verify AM tube radio transmitter!

Thread Starter


Joined May 19, 2022
I've built an AM tube transmitter. I don't have much experience in electronics. Can you please verify this circuit and tell me if it would work or how can I improve its performance? It uses an Armstrong oscillator to make the carrier frequency.

r/AskElectronics - Please Verify AM tube Transmitter


Joined Jul 10, 2017
Why is the cathode of the triode connected to the +60VDC supply? The grid will be so negative with respect to the cathode that there will never be any anode current flowing.


Joined Jun 4, 2014
I thik it would be better to move the 60uF oscillator anode decoupling capacitor to the coil side of the 2k resistor.
The screen grid voltage of the output pentode will be very low, less than 6V due to the 10k/1k potential divider.


Joined Aug 2, 2013
George, you say you've built an AM tube transmitter, and then ask us to verify the circuit shown and ask how to improve it.

Have you really built this circuit above? How did you build it - breadboard, metal chassis ? Which tubes did you use? What frequency is it designed for - can you provide the coil and tuning capacitor data?



Joined Aug 21, 2008
The last tube type transmitter I made was modulated by audio voltage applied to G2 if the final stage. Low power and not so much worry about the linearity of the upstream stages.

Yes, the voltages are apparently all over the place and apparently the result of extra- or mis-connections.