The way I grounded the negative lead was to remove the insulators from the
contact bolt and clean the paint from around the hole INSIDE the chassis,
then added a star lockwasher inside the chassis and threw the insulators
away. I never experienced any more trouble.
73, Mike N4NT
----- Original Message -----
From: "Jim Brown" <k9yc@audiosystemsgroup.com>
To: <tentec@contesting.com>
Sent: Tuesday, September 04, 2012 11:36
Subject: Re: [TenTec] Station power supply??
On 9/3/2012 8:25 PM, Mike Hyder -N4NT- wrote:
1ST CHECK YOUR AC OUTLET GROUND IT MUST HAVE GOOD CONNECTION
2ND. MEASURE FROM THE -13.8V TERMINAL TO CHASSIS, IF NO DIRECT
CONNECTION,
RUN A PIECE OF WIRE FROM -13.8V TERMINAL TO CHASSIS.
Damn! This advice is fixing a manufacturing problem that I found in all
three of the Astrons I own -- the green wire in the power cord that IS
REQUIRED BY LAW TO GO TO THE CHASSIS for safety, does NOT make that vital
connection. The reason is simple, and a common manufacturing defect -- the
green wire is soldered to the chassis lug of a terminal strip that is
INSULATED from the chassis by PAINT! In one of the three units I own,
the two pieces of the chassis were also insulated from each other by
paint.
Bonding -12VDC to the chassis causes a problem when powering a SSB rig
that SOUNDS like RFI, but is NOT RFI. W8JI pointed out this problem to me
several years ago. Ohm's Law causes IR drop in both V+ and V- conductors
that varies with SSB modulation. Nothing new. But when V- is bonded to
the chassis, and when audio accessories are running from that same supply,
the modulation of V- is added to the audio. That modulation SOUNDS like
SSB in an AM detector -- it SOUNDS like RFI. But it's not. You can hear
this modulation if you connect headphones between one end and the other of
the V- conductor of your power supply wiring.
I have long advocated bonding chassis to chassis for all equipment in our
ham shacks to minimize problems with hum, buzz, and RFI. This practice
also reduces the above problem to the point where it is not audible. .
73, Jim K9YC
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