[Amps] issue with AL-1200 output

[Steve Bookout]

Hello all,

Need some input from the brain trust.

I recently acquired an AL-1200 amp from a non-ham third party, that got 
it from the estate of silent key.  I think he was a relative, or at 
least a family friend.

Because this amp was new to me, I was taking it slow.  All is fine and 
working as it should be up to about 300-400 watts.

At that point, the output suddenly and immediately dropped to about 12 
watts, just like flipping a switch.  The 'power output' function of the 
amp's meter confirms what my outboard meter showed.

Plate current remains unchanged at about 250 ma.  Input from the K3 
remains unchanged in power level and standing wave.

I can repeat it, over and over, with both CW and SSB bias.  It takes a 
few seconds for this to happen, anywhere from 5 to 8 seconds, or so.

No vacuum relay in the output.  No noises heard; no clicks, no snaps, no 
'nothing'.

I recently had another amp given to me that had similar symptoms.  
Turned out, in that case, that the vacuum output relay was stuck in the 
N/C position and would not switch.  Relay coil was fine and pulled 
current trying to switch the contacts.

Anyone with experiences similar to this.

73 de Steve, NR4M