Just received a "new" L-7, which seems to have the following issue(s).
1. The load capacitor initially made a scraping noise, and was clearly
misaligned physically as it would only mesh i one direction of rotation. It
had some small arc marks. I spent some time working with the offending
capacitor rotor plate to bend it back into better alignment. It is now not
scraping, but truthfully all of the plates in the load cap appear to be
exceedingly close together. Is this an issue for this amp?? Is there a clever
way to test whether I have the physical problem solved before I do what I did
next?
2. On powering it up (on 220volts) I observed about 1000 volts on the
plates, with about 1100 or so in SSB position. After powering down to confirm
my line voltage was actually 220, I powered up again and created a power
supply buzz/arc, complete with light smoke, which tripped the PS circuit
breaker. Upon opening the PS to inspect, I couldn't identify the smoker
component, but noticed that one of the caps on one side of the voltage double
circuit had been clipped free--apparnetly at some time in the past.
3. Having looked at the caps, I've decided to order new ones rated at 105
degrees and simply rebuild the voltage doubler boards and also replace all
the diodes with higher rated ones. I'll raise the equalizing resistor ratings
for the caps, and intend to eliminate the equalizer resistors in the diode
strings and simply use 6amp 800 piv parts (instead of the 3 amp 600 piv),
which I assume should fit physically where the old ones do. I suppose
replacing the Drake "glitch" resistor on the hv line might also be in order.
So it will cost me about $90 in components to rebuild the supply. Anyone
have any good suggestions on how to keep from destroying components after I
finish this work {other than simply not pluggin it in}.
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