[Collins] KWS-1 Precautionary Safety Measure

[Roger Shultz]

Whenever the front panel is dropped or the side panels on the KWS-1, this 
may affect the alignment of the Mode Switch (S101)and its rear most 
terminals in proximity to the inner sub-panel.

On this switch is the -150 volt (usually around -75 volts) bias supply. The 
contact can, as it did in my case, barely contact the rear sub-panel leaving 
the cabinet hot. When this occurs, the cabinet remains hot even after the 
power supply is turned off and unplugged from the wall! This is because 
there is no bleeder on the bias supply.

So, whenever the panel is dropped, take the time to bend the S101 rear 
contacts forward as much as possible and insulate the rear sub-panel with a 
layer of black electrical tape immediately behind the switch.

I had been working on this KWS-1 and had removed the panels including having 
dropped the front panel. Everything was working fine until I reassembled the
cabinetry. When I turned it back on I had wavering grid current even in 
Standby mode and not keyed. I determined something had to be allowing the 
250 KHz to be fed through and it seemed like it was being keyed and coming 
through the keying network.

I loosened the front panel only about 1 turn on each screw and the problem 
cleared. With a flashlight I could then see the contact from S101 to the 
panel.

I was lucky and even -75 volts gets one's attention. These things can kill, 
so be careful!

73, Roger, NJ2R