[TenTec] Station power supply??

[Jim Brown]

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