[Amps] SB-220 saga continues

[Roger (K8RI)]

Alfred Frugoli wrote:
> 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.
>   
I'm not familiar with the 220 keying, but assume it's a relay that 
relies on an external contact to provide contact closure for a supply in 
the amp.
Many moons ago, I hooked my 756 Pro to my Henry 2K4.  Worked like a 
champ.  Then I picked up an Alpha 76A, it not only didn't work right, it 
had these same symptoms. Only I had to take the cabinet off the 756Pro 
and beat on the relay until the contacts opened. (well it wasn't quite 
that crude, but twas a similar operation).  I put a solid state relay 
interface between them and never had a bit of trouble since.

Oft times even when the tranceiver keying is within the ratings of the 
amp relay the voltage spike from the coil will fuse the relay contacts.  
They use some mighty tiny relays in some of these newer rigs. I assume 
some actually use a transistor for the keying.

Roger (K8RI)
> 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
>
> -----
> Visit my amateur radio contesting blog at ke1fo.wordpress.com.
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>