> Rich Said
>
> "Which contact burned? Were you present when the contact burned? ///
> The above story seems unlikely because tank potential is maximal only
> when the tank is nearly resonant. As soon as the band switch is in the
> wrong position, the tank is grossly out of resonance. Furthermore, the
> drive delivered to the tube plummets. When I turn the bandswitch in my
> 220, virtually nothing happens. The output drops. Additionally, the
> bandswitch in a 220 is continuously shorting, so how could arcing take
> place during switching?"
My guess is that the switch contact burned/arced before it ever LEFT the
position it was in. One usually does not jerk a tune C around, so the hand
movement was probably slower and less forceful than that used to move
a band switch. The current-carrying capacity of a switch contact is based
on the centering of the wiper on the stationary contact and the spring tension
applied by the wiper. As the wiper is moved off center, the tension begins
to release due to its convex shape. At some point, there will be zero tension
just before the wiper completely clears the stationary contact. If this causes
a slight resistance, fireworks are possible. Carbon build-up, corrosion, and
dirt exacerbate the problem. Sort of like Russian roulette....doesn't happen
every time. Radio Switch Corp. will not warranty a switch when it is not used
in a manual application. With the centering detents removed for motor-drive
applications, all bets are off.
Just another guess to ponder.......
(((73)))
Phil, K5PC
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|