[Hallicrafters] Tech Tip - SX-117 Chassis Ground

[Roy Morgan]

On Dec 30, 2010, at 9:38 PM, Duane Fischer, W8DBF wrote:
(Quoting an old message from me):
> One guy reports that his highly regarded TMC  GPR-90 suffered
> mightily from oscillations and poor selectivity till he
> soldered all the riveted ground tabs to the chassis.  I have
> not yet done that to mine..
>
> Roy

I later realized a puzzlement in that statement: the GPR-90 chassis is  
aluminum!  or at least is in one example I worked on.  I now have here  
a GPR-92A for alignment. Once it is running well enough, I'll see if  
it has the symptoms mentioned above, or another one:  a very strong  
signal, or the calibrator, will pull the BFO, so there is a kind of  
hole the beat signal falls into around zero beat.  A suspected cause  
for this is IF signal leaking over to the BFO and pulling it into  
synchronization when the frequencies are nearly the same.

I appreciate the tip to monitor the diode load or detector output  
while bridging bypass caps and "shorting" ground lugs to the chassis.   
I'm going to try that one, too.

Roy


Roy Morgan
k1lky at earthlink.net
K1LKY Since 1958 - Keep 'em Glowing!