4CX250B run quite well at 1500V anode voltage in the Racal TA1800 to drive
the 4CX10000D.
One 4CX350A works as a wide band pre driver, two in parallel are the tuned
driver tubes.
The amp is run with a rf feedback loop from the 4CX10K to the driver.
When once the original 4CX350A tubes of the driver were replaced on a
commercial site by the 4CX250B and the bias circuit readjusted, as the
original tubes were out of stock (only one left), overall IMD dropped from
-37 to -31db.
73
Peter
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of jeremy-ca
When run at only 1500V the IMD is acceptable. Im again making the assumption
that the screen is VR tube regulated in Eimacs1961 test.
OTOH, I know of no commercial ham amp that runs any 4CX250 at 1500V and many
hams push them above 2KV which just makes matters worse.
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