> I have a new al 1200 that I will be putting in line Wednesday . Should I
> the tube in a burn in state before applying any drive power. Thanks for
> input 73 ray nr1r
As I recall the AL-1200's 3CX1200A7 uses a directly-heated cathode. If so,
you may want to run the filament for 30-minutes without any RF excitation at
the time of first activation. I am not sure to what degree Ameritron tests
and burns-in their amps prior to shipment. The 3CX1200A7 is an "instant-on"
tube so after initial testing, you can apply excitation shortly after
applying AC power.
In broadcast transmitter applications, the typical start-up procedure
consists of applying 100% filament voltage to a directly-heated cathode for
approximately 30 minutes without Ep applied. Then, the transmitter is
adjusted to 100% power while maintaining 100% rated filament V for a period
of about 500 hours. Finally, filament voltage is gradually decreases to the
point where emission just begins to noticeably fall off.
Unfortunately, most commercially-manufactured ham amps do not allow the user
to regulate filament voltage (or heater voltage) to compensate for varying
AC line input conditions. Some amps like the ACOM 2000A allow the user to
step-through an array of input voltages through a combination of power
supply taps, and a software menu adjustment which functions as a
I have long believed that F-voltage should be adjustable by the user -- at
least a user who knows what they're doing. I suppose it's a double-edged
sword for the manufacturer since the end-user could affect F-voltage beyond
the specified range and create havoc within the warranty period.
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