Hi Stephen:
I suspect that the talkback is either the power transformer or the plate
meter. Tighten the bolts on the power transformer and either short the
meter temporarily or bypass it with an electrolytic cap. Another source of
the talkbalk would be the antenna relay. Add some capacitance to the power
source for that relay. The voltage could drop a bit under load which could
cause the relay to chatter. .
The input swr can be adjusted. If the slug makes no difference when
adjusted, then the coil is the wrong value or the slug is the wrong mu. If
both are variable, the swr will come down. The laws of electronics apply
even to SB-200's.
There is something causing the swr shift. Either the coax is not installed
correctly or the coils or capacitors are not correct. One tube could be
really bad - but then you would have other problems.
Good luck, Colin K7FM
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