Topband: Grounds and Vactrol

[Fred Cresce]

Hello,
My question before the group is about the variable termination of a K9AY loop. I am using the accepted device, the VTL5LC2. The way described from different sources is to use a 10 turn pot (about 2K ohm) for a precise adjustment of the voltage to the LED in the Vactrol.
I have been having a failure of the 10 turn pot when the voltage approaches 2.0 volts. Apparently it can't handle the current and the control zorches out and then my supply volts of 13vdc appear at the LED and it's destroyed. Is there a better way to control the voltage to the Vactrol without the damage to the 10 turn pot?
The grounding question is about the methods used to connect to the ground rod/copper tubing used in a ground radial system: I have no problem with silver soldering ground radials to the copper pipe formed into a circle at the base of an "L" or Vert. It's connecting several ground rods together and "attaching" to the rods is the question. Is the mechanical way acceptable, using the good copper clamps available in the home center? I realize that now it's a maintenance thing to be performed every couple of years to re-apply the anti-oxidant and retighten. I know that there is an Exothermic process out there that's a lot better. The "bond" is permanent ! Is it expensive? Is it difficult to use or dangerous?
Thanks for any advice.   Stay warm
Fred KC4MOP