[Collins] KWM-2 S-Meter Sensitivity

[Dave Harmon]

Hi Byron...
I would first replace V1, V3 & V7 and see what happens before doing anything
else.
I would install service bulletin 8A, B & C and then do the receiver
sensitivity adjustment from the manual.
There is a 'test select' resistor that can make a small change in the
S-Meter ckt but before changing I would ensure the rest of the rig is good.
If not already replaced....I would replace all electrolytic caps....this has
a major impact.


Dave Harmon
CCA 97-535
K6XYZ[at]sbcglobal[dot]net
Sperry, Ok.


-----Original Message-----
From: collins-bounces at mailman.qth.net
[mailto:collins-bounces at mailman.qth.net] On Behalf Of Byron Tatum
Sent: Saturday, February 11, 2012 10:44 AM
To: Collins at mailman.qth.net
Subject: [Collins] KWM-2 S-Meter Sensitivity

Hello-
    Recently I  took a  516F-2 chassis and built a new power supply using
the Heyboer power transformer and matching 3 chokes. In general I followed
Jim Garland W8ZR's build that is detailed on his website.
    This newly-built 516F-2 lowered my low-B+ coming from 325 VDC (measured
on a standard 516F-2) to 285 VDC. Plus, the filament voltage is a little
closer to spec. I am using the 125 VAC tap on tyhe Heyboer primary as my
line voltage runs between 125 and almost 130 VAC at times.
    I noticed a change in the receiver section operating a this lower
voltage: In oder to get a full scale S-Meter reading with the RF Gain backed
off fully I need to run the "Receiver Gain Adjust" pot wide open now,
whereas previous to lowering the voltage I was running the gain adjust at
about the 70% position. I do not wish to have to keep the gain adjust wide
open as the receiver has more than enough gain at 50% to 75% open on this
adjustment, but as I lower the setting of the gain adjust pot the
S-Meter full scale reading is lowered correspondingly, and quite
considerably. I plan to always operate this
KWM-2 on this newly built power supply so I need to make a permanent change
in the S-Meter circuit.
    Seems like I heard mention of a resistor to adjust the value of that set
the S-Meter full scale range. Thank you for your time,
                                                                           
    
                Byron WA5THJ
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