MAJOR T/R KRAPOUT

[flintstone mop]

Hello Friends
I had a major burnout of a T/R relay whilst experimenting tuning the linear into a 3.5:1 load on 160M. I made sure I was at legal limit at 1880, where the antenna is 1.5:1 and then moved up to 1900. The amplifier didn't seem to like the change either, and when I tried tuning there was a nasty fizzing sound from somewhere. A half hour later I discovered the what fizzed and it was a T/R relay that I use to give me a second feed to another receiver. It was a relay we would use in Motorola 300 watt FM base stations. We always had trouble with these, but they were mechanical. After hundreds of keyups every day, the stuff wears out. Not burned up contacts that I see here. I have a replacement T/R that is from another Motorola product of the 50's. It's a huge relay with huge contacts that are tied together and a 24 volt coil.
I don't know if I want to experiment with loading into a mismatch greater than 2.5:1. It may have been a voltage point for 160M. Dunno and don't want to fry things now during radio season.

fred 

[N3DRB The Derb]

I wanna get some corona dope for the t/r switch so this wont happen to me. the contacts are clean now as is the substrate of the board they are on, but some extra protection would not hurt.

[flintstone mop]

Maybe another precaution here............If you want to experiment tuning into a non resonant antenna that may show a 3:1 or 4:1 SWR, you might want to do it at a lower power, like 100 watts. 300 watts can be nasty. OR use the old standby MFJ259 and see what parameter has really changed. Extremely high Z or high reactance of some sort??? Some antenna gurus might comment here and give a little speculation what happened at MOP radio.

Fred