> To: amps@contesting.com
To: <amps@contesting.com>
> Date: Tue, 26 Aug 97 19:28:51 +0000
> The Product Reviews of the Alpha 91b and the QRO 2500DX merit reading
> since these are the first with the Svetlana 4CX800/GU-74B tetrodes.
> To be honest, I am amazed at the IMD performance of both amps; the Alpha
> is 45/49 dB and the QRO is 43/40 db for 3rd/5th orders. This sure beats
> the old 25/28 dB typical of 4CX250's.
Not by as much as you think.
All Eimac and commercial specs use dB below ONE TONE while the
ARRL uses dB below PEP.
So the numbers are really:
AL800H -43 dB third order, -49 dB fifth, -53 seventh
Alpha 91 -39 dB third order, -43 dB fifth, -49 seventh
QRO -37 dB third order, -34 dB fifth, -54 seventh
4CX250's -25 dB third order, -28 dB fifth (if your numbers are
right)
The old 4CX250 is really only seven dB worse than the QRO, but 18 dB
or more worse than an AB2 triode!
I don't have my copy of QST. What was the failure of all three amps?
Does anyone know? So far as I heard, the AL-800 never failed but did
lose some IMD performance from an earlier test when it was new, but
not enough to get unacceptable.
Did they say what the failures were for all three amps?
73, Tom W8JI
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