[Amps] info on al-1200 amp

[Vic Rosenthal]

ken cubilo wrote:

> I just put a ameritron al-1200 on line a couple of days ago. I am
> noticing that the suggested load capacitor settings are all much
> lower than the manual suggested settings, for max power output. I am
> driving the amp with about 80 watts max so I suspect this has
> something to do with it. anybody else using one of these amps notice
> the same thing?

I presume that you are testing into a 50-ohm load, right?  Notice also 
that you should always adjust the load control for a slightly heavier 
load (less capacitance) than that which produces maximum output, for 
best linearity.

If you are running the amp at less than rated input, then the impedance 
presented by the tubes will be higher (same Ep, less Ip), and you would 
expect proper matching to occur with less plate-C.  Maintaining overall 
resonance (since the plate L is fixed) would require slightly more 
load-C (this statement is going to provoke an argument, but I stand by it).

Of course, you said 'a lot lower', so knowing Ameritron/MFJ I would 
check the positioning of the knob on the capacitor shaft just to be sure.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco