The power supply will be fine with any of those measured line voltages with
any xfmr tap. However the real important voltage is the tube filament. It
must be 5.0V True RMS +/- 5% MAXIMUM. Select the tap that gives you the best
tolerance.
Carl
KM1H
----- Original Message -----
From: "James M. Daly" <punk_itup@yahoo.com>
To: <towertalk@contesting.com>
Sent: Sunday, July 22, 2007 1:11 PM
Subject: [TowerTalk] AL-80B amplifier transformer tap
> Hey guys, hope this note finds all of you well, it is
> a lovely day here in MA.
>
> Last night I install a new line voltage circuit in the
> radio room for use with my new Ameritron AL-80B
> amplifier, here are the details...
>
> 1). 2-pole common trip 20A breaker in the service
> panel.
> 2). 12-2 w/Ground NM cable out of the panel, about a
> 15' run.
> 3). 6-20R receptacle in the wall, wired Black hot,
> White hot (coded black), and bare copper equipment
> ground.
> 4). I am going to replace the factory 5-15P plug on
> the amplifier's power cord with a 6-15P for the 240V
> service, the amplifier is rated for max 10A draw at
> 240VAC and will have corresponding 10A line fuses in
> the chassis. So the 5-15P plug is all it needs.
>
> So all that is well and good; now comes my need for
> advice, as I have no experience with HF tube
> amplifiers and tapping the transformers there in.
>
> 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 in the morning so there
> was no big demand on the neighborhood grid (rural,
> limited house and few with air-conditioning, no
> businesses, and one HV line on a dead end street).
>
> Today it is a little after noon on a Sunday and I am
> reading 244VAC at the receptacle, obviously
> neighborhood demand is up compared to my early AM
> check.
>
> 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
> voltage.
> 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%
> under-voltage.
>
> So what do you guys think, is the 245VAC tap the way
> to go? Also keep in mind that I have only done two
> readings, the line voltage could drop closer to 240
> under further grid demand.
>
>
> Peace
> James - AD1L
>
>
>
>
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