I picked up a Dentron MLA-2500 a couple of months ago and have been going
thru it. The PS filter caps were a mix of Spragues and CDEs. I pulled the
old caps and ordered 8 Panasonic 220 MF 450 volt electrolytics. I got
creative with my art work and ecthed a board for the Caps and equalizing
resistors (100K 3 watt MOF). The caps were much smaller physically then the
originals. The board was mounted on .5 inch insulated stand offs. I also
replaced the rectifier diodes with 1N5408s.
I put a new power cord on the amplifier. The old one looked fine on the
outside, but when I went to change the plug for switching from 110 to 220
volt, I found that the black rubber insulation on one of the conductors was
brittle and cracked clear through the cord. When I pulled out the cord, I
found a big burn mark on the terminal strip where the cord enters the
chassis. The black conductor had shorted to the mounting screw.
I fired up the amp to give it the smoke test. No leaks so far. The meter
is showing about 2350 volts on the B+ with no load, and about 2250 volts
under load. I hooked the amp up to my FPM-300 transciever and am seeing
about 1000 watts out on 50 watts drive. I was glad to see that the 8875s
are still working. The plate current was about 650 ma.
Someone on the list had mentioned changing out the grid current multiplier
to get some more swing on the meter, so I changed out the grid current
multiplier to a 5 K resistor (the original is a 510 ohm job). I did not see
much movement on the meter when it was switched to grid current position. I
will need to check out the circuit a little closer to see what is going on.
Still need to speed the fan up abit.
A question for the group. Any special percautions on using exciters that do
not have an ALC output (other than keeping the drive down to a clean level)?
TNX ES 73
Jim Zellmer, KA0VSL
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