[Hallicrafters] SX-100 ground issue

[Troglodite at aol.com]

In a message dated 4/5/05 7:51:53 AM Central Daylight Time,  
cknight at cfl.rr.com writes:

> I recently purchased a SX-100 and was attaching a ground  connection and 
got "zapped".  I measured the voltage potential between the  chassis and my 
ground lead at 120 VAC; power cord is two prong. Would I help the  floating ground 
situation by re-wiring the power cord to a three prong, or  counld I have 
other issues; leaky cap, etc?  Any suggestions, insight would  be appreciated. <
 
Actually, there are several issues here. Yes, the line bypass capacitor is  
probably leaky, but even if it wasn't, it would under some conditions cause the 
 readings you are getting. In addition, there is often a high value  resistor 
from an external antenna terminal to one side of the line.  This was actually 
a UL requirement at one time for the purpose  of minimizing static buildup on 
the antenna terminal. The final problem is  that modern 120VAC outlets are 
full of spikes and surges that did not exist in  the 40's through early 60's. 
The old style paper/wax capacitors will eventually  fail in these applications.
 
At the very least, you should replace the line bypass or line  to chassis 
capacitors with agency approved types. (You will find them in  the Digi-Key and 
Mouser catalogs.) Your options then are to do a bit of rewiring  and use a 
polarized cord, moving the power switch to the hot lead, (It's usually  in the 
neutral.) or you can install a 3-wire cord. If the latter, you can reduce  the 
value of the line to chassis capacitor since it is only necessary for  HF 
decoupling now. (.0047 is sufficient)
 
Feel free to drop me a line if you have any questions.
 
Regards,
 
Doug Moore KB9TMY