SB-200 and no grid current

[Needham R Williamson Jr]

Jan,

I presume you have a schematic ---  the rest may sound obvious but here
goes any way.

First - if you did not build it yourself, always try to verify the unit
against the schematic.  Unplug, discharge the HV supply and get your ohm
meter out.  Make a photocopy of the schematic and get a highlighter.  The
SB-200 is pretty straight forward and is easy to trace.  Trace out the
entire schematic!  You'd be surprised at the number of mods/errors that are
found this way - now you know for sure.

Second --Or maybe this is first! Look for the obvious, burnt components,
poor solder connections and shorts.  Pay attention to the switch waffers
and input filter sections.

Third - You have already tried the tubes so that probably is not it.  Are
the power supply voltages all there and correct.  Careful - High Voltage
present! Also polarity!

Fourth - Think about the problem in it's basic form.  No grid current?  Is
the driving signal getting to the tubes? You have already traced the ckt -
now what components pass an AC/rf signal that might be open. Yup - coupling
caps. How about bad relay contacts? Did the T/R relay in the SB-200 pick
when you key'd up your FT1000.  Is the plate bias current there on key up
in SSB mode with no modulation?  You get the idea.  Systematic not just
shotgun. Plus you'll have a better understanding of the unit in the long run.

Good Luck
Rodger
N4NRW

I'll look over my SB-200 Schematic in a few days and see if I can point out
some specifics areas to look.

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