I am trying to convert a 2000D Henry RF generator built for 27.1 MHz to run on
the 15 meters band. Initially, leaving the 3CX3000A7 tube in it, I have started by
seeing what range the standard tank circuit and input circuit has. The tank coil
is tuned by a brass slug entering into it on a threaded rod. The cap is a "flapper" cap,
two sheets of brass separated by a Teflon sheet. The moving sheet is curved and
as it presses against the Teflon separator, under the influence of another threaded
rod, it flattens, and the capacitance rises.
I did a custom cal to a 5 foot length of RG-58 BNC terminated coax on
my on my AIM4170C analyser and squirted a frequency range from
20 to 30 MHZ into the RF output socket of the deck, with tank coil and flapper
cap at maximum, and then again with them at minimum. I then put the signal into into the
exciter (input) socket. The tube was still in the deck. I have put the results at:http://www.gatesgarth.com/henry/scans.zip
I can't understand why a generator set to run at a fixed 27.1 MHZ gives the
input scan that I have produced with a resonant frequency of 25.065
MHz? The input coil has a ferrite trimmer, but is untouched from when
the generator came out of working service. Should it not be at very
near 27.1 MHZ? Is my test procedure flawed?
The range of the tank circuit seems sensible.