Richard said:
"* No tuned input with g-g is not hardly engineering practice".
Well, perhaps. Let me throw some round numbers out - just for discussion.
I do not claim they are researched numbers, nor that the conclusions based
upon these numbers are correct. But, I do hope to raise some questions at
generalities spread. I recall the third order distortion level of the
4CX250 tube is about -24 db. That is not adequate. However, driving the
cathode has inherent degeneration and may improve the third order
distortion level by perhaps as much as -6 db. That would equal -30 db.
And, while I try to build amplifiers cleaner than that, that is still
acceptable and cleaner than most transceivers. There is no question that
tuned circuits in the cathode will improve the third order distortion
products by acting as a flywheel. Maybe there is a 3 db improvement or
maybe a 5 db improvement. Without the tuned cathode, the load on the
transceiver will vary substantially. But, still, the output signal may be
acceptable. I do not know for sure and have not tried it with all
transceivers. But, I am not prepared to say that it necessarily will sound
rotten.
My Alpha 76PA uses cathode drive with no tuned input. It is not a poorly
designed amplifier and continues to run fine after a quarter century. The
distortion products are acceptable and I have never had a complaint of
splatter and it looks clean on my Tektronix spectrum analyzer. It does
have some resistive loading which no doubt does help a bit.
I did not look at the circuitry - just the mechanical assembly.
I did build an amplifier once with cathode drive, no tuned input, and no
grid meter. It ran 4 x 6AG7 tubes at a couple of hundred watts input. The
problem, however, was that the 6AG7 was black and I could not see the
plates. They lasted for over a year, when the amplifier was finally
retired. The CTI amplifier looks much better than my 4 x 6AG7 amp.
At least you guys are reading these posts.
73, Colin K7FM
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