[Amps] Quad Tube 4cx800 hf amp

[R L Measures]

On May 26, 2006, at 7:50 AM, Gary Schafer wrote:

>
> Here is something that is sometimes forgotten when in the quest for  
> an amp
> with "lots of head room".
> If the amp is to be tuned and operated at its full power capability
> everything works fine.
>
> If you tune it up at its maximum capability but actually run it at  
> a lower
> level, your efficiency will be much lower.
>
> Example: you tune the amp up for 4000 watts out but only operate it  
> at the
> 1000 watt output level. If the amp has 60% efficiency at 4000 watts  
> it will
> only be operating at 30% efficiency at 1000 watts. Lots of wasted  
> power in
> plate dissipation.

Use VOX and when one stops talking, anode dissipation drops to zero  
in under a second.
>
> Also intermod products do not greatly improve by operating at lower  
> levels
> either. They are pretty much fixed in a class B or AB amplifier.  
> Actually
> they may be a little worse at lower power levels than at higher power
> levels.

Turn down the mic. gain to reduce P and, when the anode-I meter no  
longer wiggles, the amplifier is in Class A, and that's as clean as  
it gets.  If more P is needed, simply turn up the mic. gain.
>
> Moral of the story: Build the amp for the capability you are going  
> to use it
> at. Not for what it could be operated at.

Amen, Gary.
>
> 73
> Gary  K4FMX
>
>
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R L MEASURES, AG6K. 805-386-3734
r at somis.org