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.

 

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.

 

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.

 

What is the last tube? And its screen grid is at a very low voltage. Is there any anode current?

 

The 530pF value of Cx (audio input) is so small that it attenuates all audio frequencies below 6kHz.

 

Where did you get this circuit diagram from? Is it a test to see who can spot the most problems?

 

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?

Andrew

 

I thought AM usually involved a power amplifier modulating the class-C output stage through an isolating transformer.

 

I hope you have the appropriate license to use a transmitter!

 

I hope you have the appropriate license to use a transmitter!

He will not need one for a long time if he really has built that circuit.

 

I thought AM usually involved a power amplifier modulating the class-C output stage through an isolating transformer.

That is called Plate Modulation. Basically, like this.
http://www.vias.org/basicradio/basic_radio_17_04.html

 

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.