Recently put one of the W7RY QSK boards in a TL922A and used RJ1 relays for
both input and output switching in the amplifier. I think I bought the
relays at different times. Once I replaced a bad (Chinese) transistor off
of ebay that was used in the board, it worked like a champ.
For the past couple of weeks, I have found that over a period of maybe 5
minutes or so, the SWR from the input side of the amp to the transceiver
would creep up, and then finally be really high.The xcvr shut down and no
RF out from the amplifier. After a few minutes of rest, it would work
again. Occasionally after this event I would notice the 3-500's glowing
cherry red. I would have to shut the ampl down to stop what appeared to be
runaway oscillation. I think I have the output relay identified as the
culprit. Must not be making contact. What I am having a problem
understanding is why it takes a few minutes of transmitting for this to
happen. RF causing heating on the contacts on the relay ? I have the
amp upside down on the bench with the bottom removed, otherwise i would
never have noticed the tubes glowing red. I have used freeze mist and
spraying the relay will allow a short fix. So far the tubes seem to have
not been damaged.
Could someone try and explain why heat (RF) would cause this? Once again,
if I fire the amp up right now, it will put out full power for a while.
73 Doug N4IJ
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|