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[Amps] Alpha 76 input circuit ?

Subject: [Amps] Alpha 76 input circuit ?
From: Steve London <>
Date: Mon, 06 Apr 2015 08:43:36 -0600
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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.

Steve, N2IC
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