Sunday, January 17, 2016

Servicing a B&W Protax #376 Antenna Switch

I have a B&W Protax Series rotary coaxial antenna switch, model #376. It's been in use many, many years, and has been great. I've constantly abused it by switching it while under power, working into high mismatches, etc. I really like these switches, as they ground the unused antennas that are not in use.

Recently, I fired the amp up on 40m CW, not knowing that one side of the 40m dipole had fallen and was entangled in the tower. I loaded up on the dummy load, flipped the primary dummy load switch to "Antenna", and let'r rip. With my headphones on, I didn't hear the switch box arcing. I noticed my reflected power meter go crazy, pulled the cans off my ears, tapped the key, and heard that dreaded hollow sounding arc...

Since then, I noticed I had to wiggle the knob on the B&W to restore receive on the 40m antenna. I knew I had damaged the switch, and began to search a little for info about servicing the unit. Everything I found contained comments that it was in a sealed housing and could not be opened. Oh well...

I decided to tackle the project, anyway. I discovered the rear of the housing had a lip that looked something like that of a soup can. I removed the knob, center switch shaft lock nut and star washer from below the knob, the 3 screws that secured the face plate to the enclosure, and the mounting bracket.

Using a simple top cutting can opener from the kitchen, I removed the "lid" from the rear of the housing. It was one of those that removes the lid from a soup can in a way that it can be replaced and leaves no sharp edges. I was in!! I cleaned the switch with a brass brush, & sprayed it with a good dose of contact cleaner & lubricant. I wiped up the excess, blew the housing out with compressed air, and wiped it down with a rag.

I cleaned around the edge of the "lid" I removed and the edge of the switch box housing. The lid reinstalled easily, and was held in place with a small C-clamp. I used conventional rosin-core electronics solder, and re-attached the lid at several points around it's perimeter.

I reinstalled the switch into my system under my operating position, and all is like new again. I have a number of switches attached to the underside of my operating position. I have become familiar with their location, and it makes it easy for me to select from many of the antennas at my QTH. They're in easy reach, and don't clutter the topside of my operating position. This repair was an easy task, and it saved my old friend from the scrap box!