[Amps] SB220

[Paul Christensen, Esq.]

>****  The SB-220 has a current-limiting type filament transformer which
>limits inrush-I to 60% of what Eimac allows.  However, a stepstart is
>still needed because the inrush-I to the HV-transformer will eventually
>ruin the SB-220's ON/OFF rocker switch.

I ran into the same issue many years ago when I owned a SB-230 conduction
cooled amplifier during my high-school days.  The in-rush was so strong that
the ON/OFF rocker switch (with internal circuit breaker), would trip several
times until enough energy was stored into the electrolytic caps.

It was an interesting game of chance:  If you happened to turn the amp on at
or near the AC mains zero-voltage crossing, the breaker would not trip.
So...something like one in several tries would not trip the breaker.  Either
a solid-state (zero-crossing) switch or a resistive step-start with "K"
logic would have eliminated the problem in this case.  The zero-crossing
switches may work fine in some instances, but I believe the best solution
(and most reliable) is a simple step-start system.

-Paul, W9AC