[AMPS] 3CX3000A7

[k1ta@contesting.com (Bob Marston)]

GSeven wrote:

> I thought it would tune around at least 25pf bit its back all the way out.
> What should I expect to see with say 100 watts provided the tank is right?

Answer  Not much   The 3CX-3000A7 is notorius as being a Pig to drive. The
spec sheet states that 410 watts is required to drive it to 2.0 Amps of
plate current. With 100 watts don't expect much more than 500 mils of plate
current with the tube biased correctly.

As to 10 meters not tuning that is also predictable. The 3000 has an
inordinately high output capacitance. 38pf  Compare this to the 8877 and
4CX-1500A which each have values of 10 pf and its understandable that you
are not able to tune 10 meters.

Finally the plate voltage that you state you are using (6700 volts) is a
full 33% over the manufacturers Maximum recommended Plate Voltage of 5000
Volts. BE CAREFUL !

It appears that Eimac intentionally developed this tune with the objective
of keeping it out of the hands of Hams and CBers. My recomendations, if you
have this Amp running on all bands but 10 declare victory and leave it
alone. Drop the Plate Supply to 5000 volts and limit the service of this
amp to 14 Mhz and below.

73s

Bob K1TA


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