73 de Al, KE1FO
-----
Visit my amateur radio contesting blog at ke1fo.wordpress.com.
---------- Forwarded message ----------
From: Alfred Frugoli <alfred.frugoli@gmail.com>
Date: Sun, Nov 9, 2008 at 9:00 PM
Subject: Re: SB-220 saga continues - ARB-704 experts?
To: amps@contesting.com
Hello everyone,
Here's a little more of what I'm seeing after some measurements tonight.
Let me give some background on the setup for this rig.
At some point (I don't know if it was me or a previous owner) the amp relay
in the ts-940 was killed. Therefore I'm keying the SB-220 (through the
ARB-704) and TS-940 with a WriteLog MultiKeyer (the rig and arb-704 are
connected in parallel to the multikeyer ptt port). When this box exerts
PTT, it drops the voltage from 15VDC to under 1VDC (measured voltages, adn
these are within spec for the multikeyer). This keys the ts-940 as well as
the ARB-704 and SB-220.
I have a similar setup on a 2nd rig with an TS-940 (without a dead amp
relay) keying an AL-80A through an ARB704.
On the known good ARB-704 I get a lot of resistance between the amp output
and ground (250Kohm) when not keyed, and about 30ohm when not keyed.
On the known problem ARB-704 I get about 15ohms resistance weather keyed or
not.
The relay output on the SB-220 shows about 120-125v dc to ground - within
spec.
I'm happy just to replace the ARB-704 that seems to be non functioning, but
is there something in my setup that's just going to kill another one?
Thanks.
73 de Al, KE1FO
-----
Visit my amateur radio contesting blog at ke1fo.wordpress.com.
On Sun, Nov 9, 2008 at 12:16 PM, Alfred Frugoli <alfred.frugoli@gmail.com>wrote:
> 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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