Thanks for all the replies.
The amp is definetly keyed whenever it is on. I missed hearing the t/r
relay engage because of the noise of the on/off switch clicking. Whenever
the amp is on there is plate current also - confirming the suspicion. I was
thinking that I would need to recalabrate the amp meter when I had the
amplifier apart again - but obviously it's working just fine, hi hi.
I have an Ameretron buffer between the amp and the ts-940 that drives it.
When i disconnect the relay cable between the buffer and the amp it unkeys,
so my project this afternoon is to take a look at the arb-704 and see what's
going on there. The xmit light goes on/off appropriately when the rig is
keyed, but obviously it's always keyeing the amp. As soon as the center of
the rca connector on the relay cable touches the contact, the relay closes,
so somehow I've got a path to ground all the time in the buffer.
Thanks to all for the trouble shooting assistance.
73 de Al, KE1FO
-----
Visit my amateur radio contesting blog at ke1fo.wordpress.com.
On Sat, Nov 8, 2008 at 11:23 PM, Alfred Frugoli <ke1fo@arrl.net> 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.
>
> 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.
>
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