[Amps] Vacuum Relay Issues

[Vic K2VCO]

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