>SB-200, Harbach power supply board, Harbach soft start module, new Cetron
>572b tubes initially burned in for 24 hours with high voltage and cut-off
>bias and with about 10 hours of use on them.
>Turned on amp and big bang sounding like rifle shot. No smoke, no smell.
// sounds familiar.
>Turned off immediately and checked all values and voltages. All OK. No
>visual sign of arcing or burning.
>Turned on again and been working fine all week.
// If the cause had been a (disappearing) "barnacle" or (vanishing) gas,
the sound would have been barely audible, like the 'tink' in a
vacuum-capacitor when it arcs at its breakdown potential.
>Anything I should worry about? Anything I should fix?
// I would take the precaution of measuring the resistances of the
suppressor resistors and the resistances of the grid resistors. A
resistance indication of more than plus 25% suggests that there could
have been an intermittent oscillation. [note: measuring the resistance
of a suppressor resistor requires that one end be unsoldered.] If you
find signs of arcing on the 80m Tune-C padder's (100pF) switch contacts,
a parasitic oscillation is more likely -- provided that you weren't
rapidly switching the bandswitch while transmitting at full-throttle.
- If you want to try decreasing the parallel-equivalent resistance of
the suppressors, we can send you a parasitic suppressor retrofit kit to
try. Also included is glitch protection for the meters, HV-PS and the
grids. If you think its bogus, you don't owe us. Otherwise, it's $12.50
+$1 for postage.
- R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.
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