At 10:54 AM 12/3/97 EST, KM1H wrote:
>
>
>The amp will do 1800W but for tube longevity keep it in the 1200-1300W
>range. Make sure that the grid swamping resistor, R-1, is in the circuit.
>Many MLA owners cut it out to get even more power!
>
Max ratings for the 8875 are 2200 volts at 350 mA or aproximately 1500
watts input. However, the Eimac catalog (4/92) I have lists operation
at 2000 volts and 500 mA peak (per tube) with a resulting 587 watts of
"usable output" per tube. The tube is rated for 300 watts plate
dissipation ... so I wouldn't push them.
R1 was a 100 ohm wirewound resistor ... with it in place, the input
impedence of the MLA-2500 is about 30 Ohms with 40 pF shunt capacitance,
making the amplifier difficult to drive with solid state transmitters.
The amplifier requires a non-inductive swamping resistor of aproximately
50 Ohms/25 watts (to suck up about half of the drive from they typical
200 watt rig) and a 2:1 un-un (to bring the drive impedence back into
the 50 Ohm range). Even then, the shunt capacitance (tune input) can
make the exciter/amplifier system unstable on some bands depending on
coax lengths.
73,
... Joe Subich, W8IK ex-AD8I
<w8ik@ibm.net>
"Hindsight is an exact science."
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