Date: Sat, 12 Oct 2013 07:04:48 -0400 (EDT)
From: Louis Parascondola <gudguyham@aol.com>
To: amps@contesting.com
Subject: [Amps] Ameritron AL-82/1200/1500 amps mis-wired!
For those of you who might have any of these amps, they are mis wired. Seems
that pretty much all of them going back quite some time. They are not wired
according to the schematic and therefore a possible shock hazard is possible.
One might assume that when interlock switch S5 is open (cover removed) that
there is ZERO high voltage in the amp. But due to the mis wiring there is
about 400vdc which is in the power supply and on the tube anodes. I suggest
you "CAREFULLY" make the test to your amp to see if the problem exists. Simply
remove the cover and turn the amp on and look at the HV meter. If you get any
reading other than zero, your amp is mis-wired and you should consider wiring
it properly. The fix is simple. There is a blue/white wire coming from the
contactor relay going over to the step start relay at junction with R3. There
is a wire on S5 (on left contact as viewed from front). These 2 wires need to
be switched to conform to the schematic. In doing so, th
e 400vdc with S5 open goes away. Although the manual states never to plug the
amp in with the lid off, I know many of us do troubleshooting and we may
wrongly assume that no HV is present when S5 is open. If you are not
qualified to make the repair, ask someone that is to do it for you. I believe
this is a repair that should be made to all these amps that exhibit this
problem. Please be careful in making the test or doing the repair. Lou
## I have NOT looked at the schematic. Does the Interlock short the B+
to the chassis..or does it open off the 240vac to the plate xfmr....or
both....or what ??
Is the problem on older amps... or newer vintage versions?? IE: how
widespread is the issue ? Surprised somebody hasn’t fried themselves already.
Either way, the correct procedure would be.... to also chassis ground the B+
with an alligator clip. Then you know its at zero volts. Clip goes on
1st....and comes off dead last.
Then if something else goes wrong...... you are covered. If you want to be
super safe, use 2-3 clips..and grnd the B+ in two different places...like the
anodes, and the B+ end of the
string of HV filter caps. Another good place is directly between the B+ and
B- of the string of filter caps.
## Ameritron of course, should be notified. Its not a design issue, its an
assembly issue. IF you have the SNs, they may be able to track it down to a
specific employee or
group of employees. If they cant, they truly are idiots.
## So much for any kind of testing of the finished product. IE: step 1,
check interlock, does Vdc and or ACv drop to zero ? If not, check wiring
XXX.
Damned good thing they are not building medical or military or aircraft
equipment.
Jim VE7RF
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