[Collins] KWM-2

[Dr. Gerald N. Johnson, electrical engineer]

4.7 K to ground from the ALC line is the same as a short circuit in a
half megohm circuit.

Not being able to zero ALC and S-meter indicates positive bias to the
ALC and AGC lines. Most likely from controlled tubes with grid emission
but can be a hint of low bias voltage from the power supply. Can be an
indication of leaky paper capacitors. If you haven't replaced ALL the
black beauties with orange drops, you have so may faults you can't
troubleshoot them. That would include SSB distortion. The accompanying
tone probably is carrier from a screwdriver having misadjusted the
carrier null.

Check the power supply FIRST. The bias voltage section is prone to
failure from old age. The original supply uses a selenium rectifier (in
a molded plastic block with terminals and a mounting stud) that reduces
the bias voltage as the selenium rectifier ages. Failure of bias makes
the KWM-2 operate weirdly. Low voltage from the 275 volt supply causes
low gain through the radio, transmit and receive and upsets meter
zeroing. Bad filter capacitors for low voltage and bias supplies change
the power supply outputs. Generally to be lower than needed for proper
operation.

Judging from the schematic, S-meter zero interacts with RCVR GAIN
ADJUST.

Then a bent relay contact can upset everything. The original open short
form telephone relay is overly sensitive to contact adjustment and can
be wrecked by moving the wires connected to its terminals or by running
into the relay contact stack with a cleaning wand. I was told by my boss
at Collins that they had a major problem with those relays when the
central warehouse decided the boxes that the relays came in took up too
much space and so unboxed the relays and removed the protective tissue
paper wrapping. When they dumped the relays into a bin, most of the
relays that come out of that bin came out not working. Its not the relay
I would have used.

You can check relay operating with a good voltmeter and the data from
the schematic. No schematic and no voltmeter, you will only make the
radio worse.

73, Jerry, K0CQ, Technical Advisor to the CRA 
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.