Charles, you can also accomplish this by using three toggle switches. The
first one turns on the air supply, and supplies power to the second switch.
The second switch supplies power to the filament and to the third switch.
The third switch supplies power to activate the high voltage.
Can't activate hv unless filament and air are on; can't activate filament
unless air is on. At turn off, you can leave the air on for while longer if
you wish. A refinement is using double pole switches and wiring the ptt
circuit in series with all three switches to prevent keying the amplifier
before everything is turned on.
The hv on switch serves double duty as a standby switch in this case.
73,
Gerald K5GW
In a message dated 4/25/2013 11:50:40 A.M. Pacific Daylight Time,
zedkay@telepak.net writes:
Way back in my foggy memory somewhere, I remember using and amplifier
made by B & W. I think it was a "Model 1500", but I'm not sure. It
used a pair of 813's.
What I remember as unique about this amp was its "ON" or "POWER"
switch. It used a rotary switch to turn on the various functions one at a
time.
In other words: Position 1 turned on the fan only. Position 2 kept
the fan on, and lit the filaments. Position 3 kept the previous two
functions on, and turned on the HV supply.
My question is, then: What is this kind of switch called? I used
one of these switches (salvaged from an old tube tester) in my very
first amplifier, and I'd like to use one again, but for the life of
me I can't find one from my usual parts sources because I don't know
what it's properly called.
It isn't "make before break" because it never breaks the previous
positions. I thought it would just be a "shorting type", but this is
not the way any of the "shorting type" switches offered for sale operate.
I'm stumped! Any help would be appreciated.
73,
Charles - K5ZK
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