[Amps] 3-500Z amp producing output with no input, why?

[Bill Dzurilla]

Hello,

My homebrew 6 meter 3-500Z amp has made the trip to Europe.  The only visible damage was that one of the lines to the filament pin of the 3-500Z had broken off.  I soldered it back on.

The amp powers up normally but something goes wrong when the PTT is pressed.  Even with the rig set to SSB and the rig's power control fully counter-clockwise, the amp immediately produces hundreds of watts of output, even with no modulation.  In fact, the amp does this even when the RF input line from the rig is disconnected.  And if the RF input line is connected, the rig's internal power meter shows about 4 watts of output (the meter shows zero if the amp is not connected).  Also, the SWR is way off.  Barefoot, I read a 1.2:1 SWR to the antenna.  With the amp on and generating the weird output, the SWR is over 5:1.

Any thoughts on what might be wrong and how to fix?  I tested it and it was working fine just before I packed it up to send to Europe.

73, Bill NZ5N/OM9ACA