[Collins] Exploding 6146 in KWM-2

[Dr. Gerald N. Johnson]

On Fri, 2006-09-15 at 23:43 -0500, Dave, K2DP wrote:
> Food for thought, anyone have some ideas on why a 6146 would literally explode in my KWM-2 while the rig sits in the receive mode ? That is, other than the fact than the tube date code is "63-30" meaning that it is 43 years old !!!!!! Frankly, at that age, I'm not sure what any tube will do, but I am curious to know if others have experienced a similar type failure. Visual examination of the PA circuit in the KWM-2 and the 516F-2 do not show any visible HV capacitor or high wattage resistor failures. 
> 
> 73 and keep'em glowing !
> Dave, K2DP,. St. Louis

There shouldn't be anything IN a tube to cause it to explode. Its a
vacuum tube. My guess is that the tube envelope was cracked or a seal
leaked and it got gassy and since it sits with about 900 volts DC on the
plate with the cathode grounded, when it got gassy enough it drew enough
current to heat the gas which then expanded and made the appearance of
an explosion. Did you happen to notice that the getter deposit (that
silvery spot on the inside of the glass) wasn't so silvery but had some
white portions before it blew up? A definite sign of gas. Also the plate
current at idle was probably rising. What's the history of this tube?


-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer