To: <amps@contesting.com>
> Date: Tue, 19 May 1998 19:32:14 -0400
> From: "David A. Pruett" <k8cc@ix.netcom.com>
Hi Dave,
> I bought a MLA-2500 last winter just for contest expeditions. Fortunately
> it has two apparently strong 8875s in it. If they ever blow, my amp will
> be a candidate for conversion to a pair of 3CX800s.
Another thing to consider is two tubes require less airflow than a
single tube, for a given output power in a given circuit.
I doubt people are going to have enough static pressure to cool a
single tube at a full 800 watts dissipation, so the second tube
would add headroom with a given backpressure limit.
One thing to watch in these tetrode mods is regulation of the screen
and overtaxing transformer windings. One mod had very poor screen
regulation and severely overtaxed the 120 volt transformer winding.
If you think tubes are hard to find, wait til you look for a
transformer!
By the way, a two tone test with a few hundred Hz or more
tone spacing indicates nothing about intermodulation distortion
caused by poor screen or anode dynamic regulation.
73, Tom W8JI
w8ji.tom@MCIONE.com
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