Hi .... and Happy Holidays to all!! Working alot with these amps over the
past few years I came across a wiring error in the earlier models of these
amps.
The error has been corrected in newer models, but I do not know when the
correction took place. Surely if you have a early model that has a light blue
(grey looking) front panel, this error is present. Some early black front
models may also. Newer ones within the last 8 years I believe have he
correction.
What is the error? This is it....The filament transformer which also
supplies 12v for relays etc. has one of its 220v primary leads fused with a
small
fuse, the feed from the 220v line is derived BEFORE the main fuse or as soon as
it comes in from the wall plug. This can be a MAJOR problem!! Reason....You
could be transmitting and suddenly blow a main fuse, as a result, you may not
be aware of this because the lights will still be on and the antenna relay will
still operate, HOWEVER...you will be driving the tube(s) with no HV on them,
in the case of the AL-1500 this could destroy the tube. The fix is very
simple...Follow the wire that feeds the small fuse and move it from the line
side
of the fuse to the load side of the fuse, this way if the main fuse goes, the
whole amp shuts down, and you can not drive the tube with no plate voltage on
it.
ALSO......On some newer AL-1500's there are 2 grid resitors on the meter
board instead of just one. If your AL-1500 has 2 1.5ohm grid resistors on the
meter board, then your meter is reading 1/2 the grid current that is being
drawn
by the tube. The schematic shows 2 reistors, but there should only be one.
The schematic is wrong. I brought this to Ameritrons attention several years
ago, but I have not seen a change in the schematic as of yet. Perhaps lately
they have, but I havent seen it. Check your AL-1500 to see it you have 2 grid
resistors instead of one. The reason for the problem is that the meter board
for all the amps are the same except that the
AL-1500 should only have one resistor instead of 2. Unfortunetly, my
AL-1500 had 2 resistors.
Thanks for reading...........73 Louie
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