> After removing all of the tubes, meter readings are OK.
> Putting one (I
> assume good) tube back in the amp causes the strangeness
> to begin again.
> Any ideas?
When the amp has a typical grid and plate current metering
system in the B- return lead:
1.) Any short from the filament or cathode to ground causes
the grid meter to read backwards. Always backwards. This
includes a shorted tube or anything in the cathode lead
including the bias system.
2.) Any short from the B- lead to ground causes the grid
meter to read in parallel with the plate meter. The grid
meter moves forward.
This means you could have messed something up when
installing the new bias components, it could be a tube (but
it would not be all the tubes), it could be any short from
filament leads to chassis or from the transformer CT to
chassis. The best way to find it is to look carefully, and
if that doesn't work apply a current limited positive
voltage (100mA max) from the tube filament to the negative
rail at the electrolytics **with the amplifier OFF** and
unplugged and poke around.
73 Tom
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