[AMPS] Amps in Sept QST

w8jitom@postoffice.worldnet.att.net w8jitom@postoffice.worldnet.att.net
Tue, 26 Aug 1997 21:38:37 +0000

> 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 

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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