First I'd like to say I'm sorry about all the non-technical traffic. I'm
fully comfortable with technical disagreements, because everyone learns
more when issues are discussed.
No one learns anything technical from personal comments. If I've done
anything to encourage this I appologize. This has been a nice peaceful
and educational reflector.
Lee Buller wrote:
First on FET's.
Until manufacturers cure some of the overshoot in output power in some
transceivers, you run the risk of gate punch through on FETs.
One fellow ruined a few sets of 3CX800's until he found out his
transceiver was banging out almost 300 watts on leading edges of
waveforms.
Imagine what that would do to FET's.
If the rig has no or little overshoot, FETs are a good thing. But they
are not nearly as clean as most vauum tubes for IMD.
> Hey guys....
>
> What about using a tuner between the rig and the amp for those amps which
do
> not have a tuned input. My cheap little MFJ Versa Tuner will load a
noodle
> it seems.
Again the problem is the location of the network, and the type.
You need to present the catode of the tube (assuming grounded grid) with
a low impedance at the harmonics of the operating frequency, in
particular odd harmonics.
That provides a path that allows the tube to make the transition from
conduction to cut-off quickly. If you slow the response down, by placing
a high impedance in the catode to ground path, or allow that harmonic
energy to get back in the exciter, bad things can happen.
It isn't always a problem, but at times it is. As I (and others) have
said, the result is most often loss of efficiency and increased IMD
levels.
IMD is a complex issue, it is much more than looking at a set of
performance
curves or the result of a simple two-tone test.
73 Tom
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