Hello all,
I acquired an old SB-220 that has not been energized in at least 6 years and
not really used for more than 10. Cosmetically it is almost perfect.
Electrically it is supposed to be perfect, "the last time he used it". My
questions to the group are:
1. What would be the best process to bring this unit back into daily
service? I have a 10Amp 120V variac. The amp is wired to 240V, but has a
120V cordset on it. Should I energize it at 120V with it wired for 240V to
ease it into service?
2. Should I automatically, before energizing it, replace all of the
Electrolytic caps? I would rather not spend the extra money.
3. Should I increase the capacitance values in the filter caps, if
available, and if you guys think the caps need be replaced?
4. The tubes test good, but could they be gassy from sitting all of these
years? I am not very familiar with 3-500Z's, will letting the filaments
heat, and just sit there for a few hours, cooking, de-gas the tubes if they
are gassy?
5. Any other suggestions would be greatly appreciated on or off the list!
>From my reading of the archives of this list I surmise the following :
The step start circuit for the filaments is overkill.
The meter circuits should have a few resisters changed instead on Carbon
comp.because of value change over the years.
The bleeder resisters should be changed to 100KOhm 3W Film resisters, to
lower the heat dissipation.
There may be a Parasitic oscillation problem. (although I noticed that the
original builder failed to solder one of the suppressors in, it just has a
mechanical connection!)
If desired a QSK mod is available.
Don't use the ALC circuit.
This is my first venture into this power level (having a Collins 30L-1) so I
want to learn from the experts instead of on my own, the hard way.
Thanks in advance for the advice, it will be used!
73,
Eric
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