[Amps] AL 1200

[Paul Christensen]

> I have a  new al 1200 that I will be putting in line Wednesday . Should  I
> run
> the tube in a burn in state before applying any drive power. Thanks  for 
> any
> input  73 ray nr1r

Ray,

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 
quasi-F-voltage adjustment.

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.

Paul, W9AC