[AMPS] Bulletproof

[Bill Turner]

On Wed, 10 Sep 1997 19:06:30 -0500, w5ec@digitalexp.com (Hawkins,
Bill) wrote:

>Hi all
>Some time ago somebody wrote about an amp, I believe it was  the Ameritron
>AL-1200, and described it as "Bulletproof".
>Does that mean that even I can operate it and it will survive?
>Thanks
>Bill W5EC
_______________________________________________________________
Sorry Bill, I have proven twice that an AL-1200 is not bulletproof, at
least for full-power RTTY operation.  Here's what happened to mine.

On 160 meters, the plastic support rods for the tank coil melted at
the last few turns closest to the cabinet.  On 80 meters, the whole
tank coil went through a meltdown, and just for good measure, the
soldered tap for 80 got so hot the solder melted and the tap flew off
while transmitting.  You can imagine the arc that made.  $26 for a
replacement coil, but luckily no other damage.

True, this was on RTTY and it was during a contest (no mercy), so for
CW and SSB I'd expect there to be no problem.  For RTTY if you back
off the power to 1000 watts or so, it should be ok on the low bands.
On 40 meters and up, I ran full power with no problems.

Unrelated to the above, the tube blew when the amp was about 9 months
old and Eimac replaced it under warranty.  The replacement tube ran
for another year ok and then I sold the amp, still working fine.

Ameritron advertises the AL-1200 as a 1500 watt output amp, with no
qualifications.  This to me is misrepresentation, period.  If there is
a duty cycle limit it should be stated openly and honestly.  Nowhere
in their advertising or in the manual is a limit mentioned.  After
going through all this, I had a conversation with a gentleman at the
factory and I asked the question about brick-on-the-key operation.  He
hemmed and hawed a bit and then said he wouldn't run it more than
about 15 minutes at full power.  This is good advice of course, only
too late.  

In all fairness to Ameritron, in spite of these arcs and loud bangs,
there was no damage to the power supply or any other parts of the amp
other than fuses, naturally.  The rest of the amp is pretty tough, but
the tank circuit needs more cooling.  Had I kept it, I would have cut
a hole in the side of the cabinet and mounted a fan just for the tank
coils.

I now have a homebrew 8877 and an Alpha 91B with the optional fan,
either of which will run brick-on-the-key at 1500 watts out,
guaranteed.

Hope this helps, Bill.  Good luck.

73, Bill W7TI


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