On Wed, 03 Dec 1997 20:56:03 -0500 "Joe Subich, W8IK" <w8ik@ibm.net>
writes:
>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.
>
AMEN Joe. Too many hams think and use the 8875 as if it was the 8874.
Heath SB-230 owners (8873) are even worse!
>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.
Shoot Mon...I thought all riceboxes had built in ATU's
Seriously...I remember somewhere that Denny Had or one of his Injuneers
came up with a simple toroid to ground to cancel out all that nasty C.
Maybe someone here remembers the reference.
>
>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 100W and the resistor is pushing it...cut the 1000D WAY back to
70-80W.
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>
That was part of the excitement with Dentron products...it actually
required a few brains to get them 100% . Not Plug n Play !!
73 Carl KM1H
>
>"Hindsight is an exact science."
>
>
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>
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