Rich said:
"? As I understand it, the larger anode cooler diameter limits it to two
3cx800s. The larger coolers also requires moving the sockets farther
apart. Since the 78 has no tuned input, I would consider using 4cx800s
in AB1. "
The 76 only has 2 tubes and that requires moving one socket. However, the
76PA and 78 uses 3 tubes and requires no socket moving. The middle socket
is plugged and it works fine. Only 2 x 3CX800A7 tubes are necessary. The
power output is limited by the power supply.
Although the 78 has no tuned input, it has a resistive termination that
absorbs about 2 to 3 db of the sxcitation. That, plus the clean imd specs
of the 3CX800A7 tube mean that the amplifer is cleaner than most
transceivers. Distortion does not increase when the amp is used.
Before converting to the 4CX800 tubes, look at all of the safety features
built into the Alpha 99. I assume that they would not put all that
protection in if not necessary - which means that a simple tube swap to the
4CX800 tubes using a grounded cathode design and terminated grid and supply
of regulated screen voltage in the 78 would be an incomplete conversion.
As far as decrease in value, I think that would only be if the conversion
was ugly. Sloppy workmanship devalues anything.
73, Colin K7FM
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