At 02:13 AM 12/4/97 EST, KM1H wrote:
>
>On Wed, 03 Dec 1997 20:56:03 -0500 "Joe Subich, W8IK" <w8ik@ibm.net>
>writes:
>>
>>The amplifier requires a non-inductive swamping resistor of
>>aproximately 50 Ohms/25 watts (to suck up about half of the drive
>>from the 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.
>
OOPS! I was actually thinking about the typical 100 W radio when I
wrote that ... BFF syndrome! *I* learned my lesson about using the
FT-1K to drive an MLA-2500 the hard (expensive) wasy ... by cooking
a tube. The problem was most certainly due to overdrive, the "spike"
on initial key-down, and not parasitics.
I still plan to rework my MLA-2500 to better swamp the input, install
a 2.25:1 input un-un, install a HV "glitch" resistor, replace the
carbon comp bleeder string, rework the output network for improved
80/160 meter performance (working backwards from the max/min tune and
load capacitor values, the pi-network seems to be designed for about
1000 watts input on 160, 1200 watts on 80/75, and 1500 watts on
20/15/10), and, if I really get the "bug," see if I can "fix" the
plate choke to allow 17/12 meter operation.
Even then, the MLA will not be driven by the FT-1K ... it will be
a "second station" amp with a 100 watt rig. With the drive from
the FT-1K, I'll look at a 3CX1200 based commercial amplifier (or
build my own using a "tube with handles") once I find a new place
and get back on the air with anything more than an R5!
The MLA-2500 is a solid general purpose amplifier but not in the
"contest" class, particularly due to the high cost of replacement
tubes. Treat it right and keep it to 1100 watts or so of output
and it will be a reliable performer. Unfortunately, I haven't found
a suitable replacement for the 8875.
73,
... Joe Subich, W8IK ex-AD8I
<w8ik@ibm.net>
"Hindsight is an exact science."
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