Q90 blown by strong RF input on antenna line

Further to an earlier post about the vulnerability of Q90 in the µBITx, Gary
W6RAG wrote to uBITx.net today noting that the potential danger to Q90 from nearby strong RF signals is well founded.

Recently Gary was attempting an FT8 contact on 80 meters with his son about 400 miles distant.  Being unsuccessful with the µBITx, he turned off the rig and turned on his TS430 and made contact at about 60 watts output power. The ubitx remained connected to an end fed wire about 10 ft from his dipole that was in use with the TS430.

A few minutes later he tried the ubitx again and it had no output. He traced the failure to Q90. The emitter was shorted to the base just as reported by others.
The diodes in the balanced mixer will not save Q90.

Gary recommends that µBITx users disconnect the antenna if they are going to operate other transmitters with nearby antennas.

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