Howard number 3: 

Yes the AL-811H does have a tuned input and it sounds like all of this is starting to add up. 
Your right, when I tried my own tuner a couple of weeks ago, after being told that there shouldn't be a problem, the amp hissed when I keyed up on 75M after my antenna was successfully tuned. 
I did not key for very long but apparently a short keying and hissing may have been too much. 
However, when I put my friends tuner back in line and tuned up on that same band, there was nothing from the amp, transceiver or tuner. 
The SWR was 1.0/1 and my output was 600W CW. The reflected power was under 1watt. So if I'd really damaged or blown anything with my tuner, I shouldn't have been able to get full power using the 2ND tuner. 
The amp should not have come up to 740W with 75 of drive and then allow me to run my 45/50 in and 600W out. 
Like wise the other day. I tried 20M, couldn't get a high output from the amp. 
I stopped for 10 minutes or so to let things cool down and switched to 40M to try and the amp behaved as usual. The thing is if I had something done wrong, that amp would not have allowed me any output on any band. 

73: 
Mike VO1AX