I'm working on a vacuum tube AM transmitter as part of my final project for an electrical engineering class. My question is the creator of this circuit talked about putting in a tuned circuit. Unfortunately, the email address that is listed for the designer is no longer valid. My question is: I have a double-gang trimmer that I pulled from an unknown GE model (near as I can place it sometime in the 50s because of the smaller tubes) how do I incorporate it into the design so I can be able to tune my output frequency and keep it as clean as possible. I understand that this a down and dirty circuit with little to no finesse, but for my purposes, it is good.

Here is the link to the design: http://antiqueradio.org/minicaster.htm

Thanks in advance for any help anyone can provide.

:I'm working on a vacuum tube AM transmitter as part of my final project for an electrical engineering class. My question is the creator of this circuit talked about putting in a tuned circuit. Unfortunately, the email address that is listed for the designer is no longer valid. My question is: I have a double-gang trimmer that I pulled from an unknown GE model (near as I can place it sometime in the 50s because of the smaller tubes) how do I incorporate it into the design so I can be able to tune my output frequency and keep it as clean as possible. I understand that this a down and dirty circuit with little to no finesse, but for my purposes, it is good.
:
:Here is the link to the design: http://antiqueradio.org/minicaster.htm
:
:Thanks in advance for any help anyone can provide.
:
>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<
The circuit shown on the referenced webpage has a variable capacitor across the oscillator coil. Use one section of the capacitor you have and do likewise.

Rich

::I'm working on a vacuum tube AM transmitter as part of my final project for an electrical engineering class. My question is the creator of this circuit talked about putting in a tuned circuit. Unfortunately, the email address that is listed for the designer is no longer valid. My question is: I have a double-gang trimmer that I pulled from an unknown GE model (near as I can place it sometime in the 50s because of the smaller tubes) how do I incorporate it into the design so I can be able to tune my output frequency and keep it as clean as possible. I understand that this a down and dirty circuit with little to no finesse, but for my purposes, it is good.
::
::Here is the link to the design: http://antiqueradio.org/minicaster.htm
::
::Thanks in advance for any help anyone can provide.
::
:>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<
:The circuit shown on the referenced webpage has a variable capacitor across the oscillator coil. Use one section of the capacitor you have and do likewise.
:
:Rich
:
Just to make sure I'm understanding you correctly, put the other side of the capacitor across the inductor near the antenna, right?

Ken

:I'm working on a vacuum tube AM transmitter as part of my final project for an electrical engineering class. My question is the creator of this circuit talked about putting in a tuned circuit. Unfortunately, the email address that is listed for the designer is no longer valid. My question is: I have a double-gang trimmer that I pulled from an unknown GE model (near as I can place it sometime in the 50s because of the smaller tubes) how do I incorporate it into the design so I can be able to tune my output frequency and keep it as clean as possible. I understand that this a down and dirty circuit with little to no finesse, but for my purposes, it is good.
:
:Here is the link to the design: http://antiqueradio.org/minicaster.htm
:
:Thanks in advance for any help anyone can provide.
:
= = = = = =

It appears to me that the author was referring to the tube's plate RF choke as a candidate for "improvement" with a tuned circuit.

"...RF choke >1mH (will be replacing with tuned circuit for better performance and lower
spurious output) to B+..."

A parallel LC circuit in place of the choke coil would have maximum impedance when tuned to resonance, so it would tend to ignore the selected frequency but somewhat attenuate "off frequency" components (by passing them to the B+ bus), while still passing the DC needed to bias the tube.

Resetting the oscillator's frequency (via the variable cap shown on top of the cake pan chassis) would also require retuning the plate LC in order to maintain maximum output power/off-frequency component rejection. That seems like a "feature downside" to me. The low-pass fixed RF choke used in the circuit seems like a practical compromise.

It would require a spectrum analyzer to accurately (and quickly) assess the utility of this feature.