You have done a good job of evaluating the situation, Kevin. I can add a few
comments:
I purchased one of the first AL-1200's in the mid-1990s and used it for RTTY
contesting. I ran it at close to 1500 watts at all times. I could not get quite
1500 out with the TX I had, a TS-850S/AT, but I got about 1400-1450.
After I had it about six moths, I heard a loud pop and the lights went out. Long
story short: The tube had failed. Ameritron replaced it under warranty and the
replacement worked fine the rest of the time I had the amp. On all the amps I
have ever owned (about a dozen) this is the only tube that ever failed.
But here's the Achilles heel of the AL-1200. The low band tank coils used
undersized wire and overheated. One time on 80 meters during a RTTY contest the
solder holding the tap to the main coil melted, causing a nasty arc. I
resoldered it and there was no permanent damage. Think about how hot a coil has
to get to melt solder!
The more serious failure occurred while CQing on 160 meter RTTY, not during a
contest. There is no tap to let go so the whole coil overheated and melted the
polystyrene rods holding the coil together, again with a massive arc and lights
out. When I removed the cover it looked like a bunch of silver spaghetti inside
:-) By then the amp was out of warranty so I had to purchase a new coil from
Ameritron at a cost of about $26.00 as I recall. I replaced the coil and there
was no further damage so the amp was back to normal.
At that time the designer of the AL-1200, W8JI, was a member of this reflector
so I asked him about it. His reply - I'll never forget it - was "Well, who works
160 meter RTTY?". Obviously he was talking to one.
I realized the amp was not going to do what I wanted (RTTY contesting) so I sold
it to a CW/SSB guy and as far as I know he was happy with it.
If you look at QST ads from that period, they do not mention any limitations on
duty cycle for the AL-1200. Now they do. I suspect my experience may have helped
cause that change.
Later on I got to thinking I could have cut a hole in the side and mounted a fan
to blow directly on the tank coils. Maybe I should have.
After selling the AL-1200 I had a series of commercial amps, an Alpha 91b and
89, and a Command HF-2500. The Alphas both did fine on RTTY contesting, the
HF-2500 fell short a couple of times (smoked toroid). I then got into
homebrewing and after a couple of false starts I now have an 8877 amp with heavy
solid copper coils and an oversized blower and it will run brick-on-the-key all
day, forever.
Finally, I am a happy camper.
So that's my story, hope this helps.
73, Bill W6WRT
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