Hello Tom:
I would agree with Vic that hot switching is a potential cause for contact
failure in relays. It is possible that the Emtron circuit is not properly
designed, and this is a root cause of the problem.
Of course, this is also a potential cause of failure of your tetrodes. Have
you determined whether the input or the output relay is failing, or both.
If it is hot switching, I would think the output relay would be the first to
go, and the amp is not being by-passed properly for receive.
Your transceiver may have the ability to delay the output of rf until after
the amplifier has been switched to transmit. The delay is adjustible on
many models.
Take a look at the switching scheme for the amp, and see what kind of
sequencing scheme they are using, if any. If you already have their latest
circuitry, you will either have to redesign the sequencing, or add some
delay into your rf output timing in your transceiver to prevent recurrance.
I would doubt that running full power will add anything to the life of the
relays.
73,
Mike
W2AJI
----- Original Message -----
From: "Vic K2VCO" <vic@rakefet.com>
To: "K5RC" <tom@k5rc.cc>
Cc: <amps@contesting.com>
Sent: Monday, December 01, 2008 12:48 PM
Subject: Re: [Amps] Vacuum Relay Issues
> K5RC wrote:
> > I use Emtron DX-4 amps in my contest station. I chose them to ensure my
> > guest ops do not blow them up. They have excellent fail-safe protection.
> >
> > One by one, however, I am having problems with the vacuum relays. They
are
> > developing intermittent contact on receive. Banging on the front panel
is a
> > temporary cure.
> >
> > Emtron's remedy is that I need to run the amps at full output to have
them
> > operate effectively and reliably. I choose to run them at the legal
limit.
> >
> > That notwithstanding, I understand that there are vacuum relays that are
> > designed for low-current applications. Also, Emtron mounts the relays
> > vertically instead of horizontally (as Alpha used to do). What is the
> > experience of the group on the physics of vacuum relays?
>
> Hi Tom,
>
> They always seem to fail this way.
>
> You should (probably already have?) checked for hot-switching. Make sure
the time between
> the amp-out signal from the exciters and the onset of RF is long enough. I
don't know what
> kind of vacuum relays they are using, but the Jennings RJ-1 / Kilovac HC-1
type require
> about 8 ms minimum if you don't use some kind of speed-up circuit.
>
> I don't see how running more transmit power would affect the receive side.
>
> Some people have suggested that reversing the coil leads can give them a
new lease on
> life. If the problem is caused by something getting magnetized this might
help.
> --
> 73,
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco
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