The TS-430S sometimes suffered from intermittent receive conditions, due to
the failure of the contacts in the receive bandpass filter. The recommended
cure was to run a small amount of dc through the relay contacts. This same
solution can be easily adapted to the relays used in amplifiers.
Since the rf can be ac coupled through capacitors, the dc can be run through
the contacts at the same time the rf is being switched. Large open relays
are used in amplifiers because they are relatively cheap, generally trouble
free and easy to clean the contacts. Most of the time, the relays work
fine. They just need to last as long as the operator. If they continue to
work, leave them alone. If the receive contacts generate a high resistance,
and if you do not want to open everything up and clean them, you can prevent
further problems by switching a dc voltage through a resistance and/or rf
choke, and use a capacitor to couple the rf. The choke and resistor
combination must have enough total impedance to decouple the 50 ohm rf.
If the high resistance relay contact does not occur very often, it is not
too bad to open the amp up, clean the relay contacts, oil the fan motor,
clean off the dust, look to see if the hole in the tube plate is growing,
praise the suppressor and generally see if the high voltage bleeders are
still functional.
Colin K7FM
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|