>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?
>
check the breakdown V with a high-pot tester. 1000v is enough for the
Load-C. 3500v is enough for the Tune-C.
>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.
>
Clearly an act of sabotage.
>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.
6A diodes are not needed in a 0.800A ps.
>I suppose
>replacing the Drake "glitch" resistor on the hv line might also be in order.
>
I would use a 10-15-ohm 10w glass coated resistor for glitch duty. Over
3kV, I would use 2 in series.
>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}.
>
Using the old 600piv diodes to protect the new electrolytics might be a
good idea.
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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