This evening I wound a 'final' coil which consists of 21 turns for the loading coil and approx 9 turns for the link coil. I noticed that the link coil turns were not that sensitive to the performance of the Tx.
Measurements as follows:
Power output into my attic antenna = 4.2 watts
Cathode current keydown = 30mA
Cathode current keydown with crystal removed (ie not oscillating) = 36mA
Plate voltage key up = 339 volts
Plate voltage key down = 326 volts
Screen voltage key up = 163 volts
Screen voltage key down = 148 volts
Frequency of operation = 7041.98 Khz
Cathode voltage key up with crystal removed (ie not oscillating) = 34volts
Cathode voltage key down with crystal removed = 8 volts
Cathode voltage key up with crystal operating ( ie oscillating) = 34volts
Cathode voltage key down with crystal operating (ie oscillating) = 8 volts (frequency changed when probe placed (indicating impedance loading)
Control grid voltage key up = 0 volts
Control grid voltage key down = - 18.8 volts (I assume this is an inaccurate RMS value?)
NOTE: Most interesting was that the frequency of operation was shifted to what appears to be the natural operating frequency of the crystal. ie 7040Khz when I connect the voltmeter across the control gris. Could it be that the additional load impedance of the meter was driving the control grid properly negative biased. In other words perhaps the negative bias of the control gris is not sufficient.
Next try adjusting the negative bias. I tried a number of combinations but in the end I was not able to really improve the performance.
I completed the coil construction and reassembled the Tx back to its original form. Now working very nicely at the above parameters. Next I will take some pics of my current vintage station including my HQ180 Hammarlund RX.
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