So..
Here is where I am with the DX-100. I have been operating it with a pair
of 2E26s where the 6146s live and feeding those from the low voltage
supply. When I completed the recapping of the high voltage power supply
the finals immediately started giving me trouble. So I disabled the high
voltage and installed the changes to run lower power (much lower power)
from the 2E26s while I sort out the trouble.
When I turned on the high voltage I got a nice upscale reading on the
plate voltage meter (front panel of DX-100). No smoke. No sizzle. "Is
that meter right - over 900 volts"? The metering resistors getting old.
I let it run for a while when I was nearby and nothing bad happened.
Then I installed the 6146s and it was downhill from there. Finally I
took some voltage reading and the plate voltage is over 975 volts! That
exceeds the rating of the caps and the rating of the 6146s. I did not
solid state the plate supply rectifiers (nor any of them).
I had used four caps rated at 450 volts/100 uF. They were in two pairs
series parallel for 100 uF/900 volts. Some hams cautioned me against
using so much capacitance. So I removed one pair of the caps and ended
with 50 uF at 900 volts. The plate supply remained over 950 Volts until
I keyed the transmitter when it dropped below 900 volts as might be
expected.
6146s might tolerate higher voltages and the caps might too, at least
for a while. Maybe some other parts in the circuit won't. I *AM* having
erratic behavior from the finals (6146) that I did NOT have before. I
measured my line voltage at 129 volts. For my next trick I am going to
start applying bucking transformers. I've noticed my Kenwood T-599 has
been making some subdued power supply noises and have thought to recap
it as well. Where that plate supply used to read 825 volts it is now is
making 900 volts. Yes..bucking transformers all around. I have used that
approach before to reduce the voltage when a transformer I had on hand
came out a little to hot for the intended application. Now I'll use it
to tame the wild utilities in my ham shack but with bigger transformers.
I should get a discount from the electric utility for having to do their
work for them.
73,
Bill KU8H
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|