[1000mp] System gain in the 1000MP station

[Tom Rauch]

>         We're talking about system gain in an FT-1000MP station. The
> question has arisen as to whether one might use a different tap on the
> transformer in an AL-1200, and whether the use of a higher plate
> voltage endangers capacitors or other components in the AL-1200.
> 
>         Unlike the Mark V (higher output), the plain MP and AL-1200
>         here
> don't seem to get much over 1100 watts out on 10 meters (the meter
> says 3550 volts on the plate). 

Early AL-1200's benefit by using lower impedance cable between 
the tuned input and the tube. Ameritron now uses two 50 ohm 
cables in parallel in that area. This mod mainly improves efficiency 
on ten meters by reducing the RF impedance the tube filament 
looks back into.

While I have operated my personal AL-1200 on the 220 v HV 
transformer tap for many years (since 1985), the policy is to not 
recommend it. The AL1200 will take a lot of abuse, as long as it is 
loaded heavily enough.

If you seriously underload the amp, you run the risk of damaging 
the band switch or tuning capacitor from excessive voltage. When 
"underloaded" the tank circuit builds up too much stored energy, 
and something can eventually arc.

The best way to load the amp is to make sure loading is set far 
enough clockwise so full available drive (even 200 watts drive will 
actually not hurt it) will not exceed 250-300mA of grid current.

The single most destructive thing for all amplifiers is to couple them 
too lightly into the load, or have the load fail even for a fraction of a 
second during operation.
73, Tom W8JI
W8JI@contesting.com