[Amps] SB-220 saga continues

[Alfred Frugoli]

Hello everyone,

So it seems I've got a problem with my SB-220.

When the amp is off, but connected in the RF path, everything is fine.

When I switch the amp on I've suddenly got lots of attenuation happening on
the receive path.  Transmit seems fine - amp tunes OK etc.

My first suspicion was that there were dirty relay contacts on the receive
side.  Cleaned the contacts with no success.  Then I realized that the
problem only occurs when the amp is on.  So a trip to the schematic tells me
I don't understand.  In the RX mode the RF path through the amplifier should
be the same as when the power is on.  So I'm not sure where my attenuation
is coming from.

Just testing it a few minutes ago I can make an S5-7 station almost
completely disappear by turning on the amp, so I've got somewhere in the
area of 20db of attenuation happening!

Thoughts?

Thanks.

73 de Al, KE1FO

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