> manufacture of these amps. They are very well built and should last a
> long time. It is easy to criticize the design and used of these
> tubes, but they are the same tubes used by the KWS-1 - and that brings
> tears to the eyes of Collins lovers. I wish my home built amps looked
> as good. One advantage of these amps over a wonderful new Alpha is
> that a ham with minimum test equipment could service them himself
> using inexpensive components.
I'm not so sure you looked all that carefully.
Would you say it is "well built" without a control grid current meter
to monitor the grid current? What about cathode matching? The 4CX250
is not that clean a tube anyway, used at Eimac's specs in a circuit
where the user knows what is going on. I wonder how it is when you
limit the power by pulling the grid out of regulation, so you "don't
need ALC" as the designer advises.
I'd look twice at performance certified by anyone who thinks current
limiting on the screen or bias moving around takes care of excessive
drive, and does not cause excessive IM products. Wouldn't you?
> Would the amplifier have brought the same questions and challenges if
> it had a Collins label on it?
It would from me, if Collins drove a cathode directly without
swamping or tuned input. Especially is the Collins manual told me to
drive it as hard as I wanted, and let the screen limiting adjust to
compensate. Or if they gave me some silly nonsense about a "better
sound coming from gas regulators".
> The 4CX250 tube is not known for great imd performance. The Collins
> rig used feedback to improve the bottom line. The CTI picks up some
> performance using cathode drive, since that will add degeneration.
> And, even though it does not use a tuned input, I believe the 3rd
> order distortion level would be close to or below -30db. Maybe that
> is good enough.
I believe I will win the Lotto tonight.
My guess is it is somewhat better than 2-sweep tubes driving four
sweep tubes or a Texas Star solid state amp, and a conventional GG
power grid triode like the 3CX800A7.73, Tom W8JI
W8JI@contesting.com
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