> I just got me a good second hand Heathkit SB220, wow.!!!
>and I HATE to turn it on, because it all turns on at once.
The SB-220 was designed to be turned on this way--provided that the HV is
initially set to the low-tap. .
>The Filaments and the HT all together, those poor 3500z dont know whats
>hitting them
>when I throw the on switch.
The measured 3-500Z filament inrush current in a SB-220 is about 60%
higher than the normal filament current. Eimac says that the limit 1s
100%.
>
>Has anyone some info on the hows and why's of this amp please, or should I
>say
>Mod's for it, especially a STAND/BY Switch.
>
A standby switch offers no protection against anything, David.
- An article about the SB-220 appears in the 11/90 and 12/90 issues of
QST magazine. A high speed switching circuit that is suitable for
updating the SB-220 appears in the "The Nearly Perfect Amplifier", in the
1/94 issue of QST.
R. L. Measures, 805-386-3734, AG6K
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