Well Ken............I don't think anyone will argue other than Alpha are a
specialist amplifier company. This is what they have to say in the 87A
Operating Manual:
"ALC is a system used in transmitters which is similar in operation to AGC
in receivers. When the signal at some reference point in an amplifier chain
exceeds a preset level, a bias voltage is generated and used to reduce the
gain of a preceding, low level driver stage. The effect is to more or less
limit drive and output to the preset level.
ETO does not generally recommend the use of ALC from amplifier to tranceiver
because smooth, distortion free operation requires that the characteristics
of the ALC bias source be matched to those of the controlled stage. But
tranceiver ALC control characteristics are not standardized; each model has
its own unique gain and dynamic characteristics. (Internal ALC in
tranceivers works well because the ALC source and controlled stages are
designed together as a system.)
ALC feedback from Alpha 87A to tranceiver normally isn't necessary because
the power output of most modern tranceivers can be quite accurately
controlled ....and because the Alpha 87A's grid current limiting system
easily absorbs occasional drive peaks. Extensive tests with TS-859, TS-940,
TS-950, IC-761, IC-781, FT-1000 and TR-7 tranceivers have revealed no need
for Alpha 87A to tranceiver ALC feedback to achieve excellent results.
However, the 87A does incorporate an excellent and versatile ALC generator
so that the rare cases where tranceiver output cannot be controlled
adequately usually can be handled by using the ALC feedback if the
tranceiver has an input for negative-going-from-zero ALC. (This type of ALC
is standard with most modern tranceivers)
In this case connect the tranceiver ALC input to the Alpha 87A's phono-type
ALC jack with a shielded cable and turn the ALC adjust pot fully clockwise
to start (except set to mid rotation when using Icom tranceivers).
The adjustment goal is to use the smallest amount of ALC feedback (the least
clockwise rotation of the ALC pot) that will eliminate overdrive faults and
distortion. No hard and fast universal procedure exists but the
following.................."
I have had my 87A for 10 years, I have used it with a very wide range of
tranceivers and have never found it necessary to utilise the 87A ALC output.
FWIW
Bob, 5B4AGN
----- Original Message -----
From: "Ken Brown" <ken.d.brown@verizon.net>
To: <tentec@contesting.com>
Sent: Thursday, August 19, 2004 11:38 PM
Subject: Re: [TenTec] re Ten Tec amps and ALC
> BTW, the amps made by specialty companies (Command for example) include
> ALC circuits, no doubt so they may be operated with the widest variety
> of rigs possible.
>
> Can anyone quote a manual from an amplifier that states what the ALC
> voltage and polarity is? How many volts and what sign are supposed to
> reduce the exciter gain by how many dB? Or some other specification to
> explain whether the amplifier's ALC output will work with a given
> exciter's ALC input. Do any of the amplifiers have selectable jumpers or
> DIP switches, or potentiometer adjustments to set them up to work with
> various exciters. Do they have a chart where we can look up our exciter
> and set the ALC up to work with it? Or is there a standard that is never
> stated, so that we can just assume that it will work right?
>
> DE N6KB
>
>
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> TenTec@contesting.com
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>
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