I have recently converted an Alpha 76 to a pair of RFConcepts (Alpha)
3CX800A7LG's . It is a little difficult to drive, taking every bit of
100 watts input for 1500 watts output on the high bands. I am wondering
if I could do better with a change to the input circuit.
The Alpha 76 input circuit was changed to the low-drive mod many years
ago. The resistor pad measures about 95 ohms, so the resistors haven't
drifted much. What about the toroidal transformer that Alpha used ?
Without having to disassemble and reverse engineer it, can anyone tell
me more about that transformer ? It seems that for a pair of 3CX800's we
need to match the 50 ohm input from the driver to the ~28 ohm input of
the pair of tubes. Yes, I know tuned input would be better, but that
isn't going to happen.
BTW, other than the drive issue, I am very pleased with the RFConcepts
3CX800A7LG's. When I did the conversion, I also added the K6XX grid
current protection circuit.
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