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.
Alpha's protection circuitry is impressive and so is the 4yr warranty. It
also is full QSK. Component size is evident in the photograph along with
the dual section Tune cap which allows smooth tuning on 10-15M.
The QRO is a horse at 90 lbs. It has a large RadioSwitch bandswitch, a
Pi-L, good fault protection and full QSK. It carries a 2yr warranty.
Also reviewed is the Ameritron AL-800H which uses two 3CX800A7's. By
comparison to the other two amps it is much smaller, lighter and less
robust components. It is only 2 lbs heavier than the SB-220; 7 lbs
lighter than the Amp Supply LK-500ZC and a whole 25 lbs lighter than the
AL-82. Not the heft I would have expected in an amp in the 2200-2500W
range. I would be a bit concerned about long term reliability in a
contest environment as compared to the AL-1200/1500. The warranty is only
1yr. Only time will tell.
Of particular interest is that all 3 amps experienced failures during
testing which IMO is a bit bizarre.
Anyway, it appears that those Russian tetrodes can stay up with the best
Eimac has to offer in GG triodes.
73....Carl KM1H
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