Has anyone actually traced out the real schematic from an older commander
hf-2500, around s/n 435??? The one in the book is not complete (parts list
missing stuff) nor correct. there appears to be lots of extra stuff on the
control board, probably for stuff not used in this amp like qsk or grid
current protection. I can't find the rx cutoff grid leak resistor nor the tx
bias zener and the relay contacts that should switch switch them don't seem
to be connected. And the connections of the plate current shunt and meter
look backwards.
When the amp died the transformer shorted primary to secondary causing a
quite bright arc through the 1.5a B- fuse. I have had the transformer
rewound but now when I power it up it doesn't make full power and in rx the
idle plate current is about 400ma, so I am assuming the bias to the cathodes
is messed up. So far I have found that a 200ohm 10w resistor that is in
series with a 1n54?? diode on the power supply board going from B- to ground
is open, but the diode seems ok. I am assuming that this is the replacement
for the grid leak that should cut off the tubes in rx. but then there are
some other things on the control board that may also be generating a bias
voltage that I haven't identified yet. Anyone puzzled one of these out???
David Robbins K1TTT
e-mail: <mailto:k1ttt@arrl.net> mailto:k1ttt@arrl.net
web: <http://wiki.k1ttt.net/> http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or <telnet://k1ttt.net/> telnet://k1ttt.net
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