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Technical Tips from Mark W. Persons
AM and FM Transmitter Pushbutton Switches

Most older Collins/Continental AM and FM transmitters use pushbutton switches for filament on/off and plate on/off.  According to Continental, those switches are no longer available.  What do you do when a switch or switches need to be replaced?    
A bank of two smaller switches, mounted on sheet aluminum, is my solution to the problem.    
Here are photos of the two sheets of aluminum required to get the job done.  The top sheet has holes larger than the bottom.  That top piece goes on the back side of the transmitter's control panel.  The larger holes are needed to accommodate the mounting nut for the switches.


A closer look shows the two sheet metal pieces that will clamp into the original 7/8" x 2-5/8" rectangular hole using 4-40 hardware.  

The switches are EAO 31-151-025.  Other brand and type of switches could be used in this application too.  In the case of the filament off or plate off switches, they need to be normally closed while the filament on and plate on switches need to have normally open contacts.  Lamps need to be 24 or 28 volts.

A back view of the switch plates.  You can see the switch mounting nuts just clear the rear plate.     
This is what it looks like when mounted and wired into an FM 25 KW transmitter.


A final photo from the front.

You can build these yourself.  

A version using Licon 05 series pushbuttons.  These have labels too.

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 
Mark W. Persons   ham W0MH      

Questions?  Email Mark Persons:       

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