On 7/27/2012 7:11 AM, Jim Hargrave wrote:
> Duh...
> Why not just use the RF PWR adjustment on the front of the transceiver and
> save all that costs and wasted heat dissipated by the attenuator.
>
> "Discipline" is the keyword. With proper drive power management, most
> linears will operate trouble free for decades.
>
> I have a Clipperton-L (1980) with the original tubes. I also have a
> homebrewed 4-400(2) that I built in 1979. I did not even bother to include
> an ALC circuit. Both have been trouble free.
>
> 73s de Jim
> W5IFP
>
>
Jim,
The issue isn't so much lack of discipline as it is the power overshoot
of the internal ALC circuits found in many modern solid-state
transceivers. Yes, a disciplined operator can dial back the RF drive on
his rig to the proper, but if the ALC loop in that transceiver
overshoots on the leading of the RF envelope, ceramic tubes with
sensitive grid structures or the solid state devices, both of which are
found in many modern amplifiers, can be damaged. That's the one nice
thing about the older glass envelope tubes like the ones in the
amplifiers you describe. They tend to be more forgiving with respect to
short-term over-drive. Still, even if the tubes can take it, this sort
of power overshoot can cause unwanted distortion (key clicks, IMD, etc).
73, Mike W4EF....................
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