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[Amps] AL-80B transformer tap

Subject: [Amps] AL-80B transformer tap
From: "James M. Daly" <>
Date: Sun, 22 Jul 2007 23:40:50 -0700 (PDT)
List-post: <>
Hey guys, I was pointed here by someone on the
TowerTalk list, so if you are seeing this question for
a second time please excuse me.

Saturday night I install a new line voltage circuit in
the radio room for use with my new Ameritron AL-80B

At that time I checked the new circuit with my DMM an
"Ideal TestPro 361" (True RMS reading). At the
receptacle on the wall the reading was 248VAC across
the two hot legs, it was 1AM Sunday so there was no
big demand on the neighborhood grid (rural, limited
houses and few with air-conditioning, no businesses,
and one HV line on a dead end street).

Yesterday a little after noon on a Sunday I was
reading 244VAC at the receptacle, obviously
neighborhood demand was up compared to my early AM

Now this morning, 2am Monday I am again reading

The AL-80B amplifier has taps for 240, 245, and
250VAC. So the question is which one to select?
Keeping in mind the local grid demands determining how
much voltage potential will be presented to me, during
the varied hours of my operation.

1.) The 240VAC tap seems out because either way you
will be hitting the amp with a 1.64% to 3.23% over
2.) I am thinking that the 245VAC tap would be the
choice to make; the line voltage might be a bit soft
at times of high grid demand (0.4% under-voltage) but
that is awful close, 1.20% over-voltage of the 248VAC
potential during those late light hours on the low
bands shouldn't hit the amplifier to hard.
3.) The 250VAC tap also seems like a poor choice as
either way the amp with a 2.46% to 0.80%

So what do you guys think, is the 245VAC tap the way
to go? Also keep in mind that I have only done three
readings, the line voltage could drop closer to 240
under further grid demand. It was suggested to me by
KM1H to watch the effects on the tube filament
voltage, but I do need a starting point, and I am
quiet willing to admitt that I lack experience. 
James - AD1L

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