[Amps] SB-220 metering

[Pete Smith]

My old faithful SB-220 has been (and continues to be ) running just 
fine.  Today, however, I noticed that the plate meter was sitting about 40 
ma above the 0 line.  It seems to be a mechanical change, because it sits 
there with the amplifier completely off.  But here's the rub -- the resting 
current, which had read 120-130 ma, is now (with the meter readjusted to 
put the needle back on zero) only reading about 70 ma.  At 110 watts from 
the exciter, grid current is ~135 ma and plate current 750 ma, showing 
about 1250 watts out in SSB position -- in other words, apparently healthy.

It seems unlikely that the diode string (I have the Harbach metering board 
which replaces the bias zener with a string of diodes) is having problems, 
so is it more likely that the metering has changed?  Is there any 
connection with the change in the mechanical zeroing of the plate meter?

It occurs to me that a couple of years ago the multimeter stopped working 
in the relative power and HV positions -- it still works for grid 
current.  Could the switch be progressively failing, since that's about the 
only component in common between the two metering functions, it 
appears?  If so, does anyone know of a replacement switch with the proper 
indexing to match the panel?

73, Pete N4ZR
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