[1000mp] Mark V Class A operation

[Al Toothaker]

>From The prior post, not mine!
Al
N6TA

...When an amplifier is operated  CLASS "A", it will be HOTTEST at ZERO
output power,
because ALL of the D.C,  power input will be converted to HEAT. (unlike a
class AB,
or class B, or C amp,  the current, or D.C. input power, to a class A stage,
does NOT increase/decrease  with R.F. power demands, but REMAINS CONSTANT,
regardless of output, so  operation is MOST EFFICIENT (Cooler) at MAXIMUM
designed output power. If you  desire to operate a LINEAR AMP, the YAESU
QUADRA has
an INPUT R.F. power  attenuator, so the exciter may be operated EFFICENTLY,
otherwise, if  significantly lower output is desired, the class A D.C. bias
point
should be  reduced for the lower level, however operation at NORMAL output
in
class A would  NOT be possible unless full bias were restored....
-KC3VO, Bob Curry, Adelphi,  MD-U.S.A.


-----Original Message-----
From: 1000mp-bounces at mailman.qth.net
[mailto:1000mp-bounces at mailman.qth.net]On Behalf Of Rob Atkinson, K5UJ
Sent: Sunday, August 29, 2004 19:27
To: All about Yaesu 1000mp
Subject: Re: [1000mp] Mark V Class A operation

I looked through the ft1000 yahoo group for the
post about class a operation and could not find it.
maybe someone else can explain
why when in class a, the pa runs cooler with more power
rather than less.  I just remember this engineer saying that
but i could not begin to repeat why.  anyway, i think if
that is true, there are class a failures because hams don't
understand or realize that, and when it gets hot they crank
down to power thinking it will run cooler and make things worse
instead.

73,
rob/k5uj



----- Original Message -----
From: "Rob Atkinson, K5UJ" <k5uj at mc.net>
To: "All about Yaesu 1000mp" <1000mp at mailman.qth.net>
Sent: Sunday, August 29, 2004 8:41 PM
Subject: Re: [1000mp] Mark V Class A operation


> I am not an expert.  I have heard of people frying the pa in class a
> operation.
> A friend of mine and I tried class a and the heat sink got hotter than we
> felt
> comfortable with so we abandoned it.  I have heard of people blowing the
pa
> when cranking the collector current pot (power pot on the front panel) all
> the way
> clockwise and yacking away in class ab.  I have always run mine a little
> below that.
>
> Now you know where I was a few weeks ago.  I (or maybe it was someone
else)
> asked
> something related to this on the yahoo group for yaesu and a guy who
seemed
> to be
> very knowledgable about RF design said that in class A, you actually do
more
> damage
> running at low power, and you stand a bigger chance of frying
> the pa if you dial back the watts in class A, which was what we had done,
> thinking less
> watts, less heat.  We noticed that running the rig in class A at 30 watts
or
> so didn't make a
> difference; it still got real hot.  Besides, for me, that would not help
> because my amp needs
> at least 75 w. to be driven as it is not one of these ceramic tube screen
> driven amps.
>
> he seemed to think it should be run at 75 watts.  i did not understand
> it and it is a paradox of class A I guess, and decided to stay with AB to
be
> safe.
> if I can find his explanation I will try to send it.
>
> rob/k5uj
>
>
>
>
> ----- Original Message -----
> From: "Jim" <pywacker at fuse.net>
> To: <1000mp at mailman.qth.net>
> Sent: Saturday, August 28, 2004 12:28 PM
> Subject: [1000mp] Mark V Class A operation
>
>
> > I have heard some hams on the air (just a few) along with some limited
> > posting on some boards about the use of the class A feature of the Mark
V
> > contributing to the loss of finals in these rigs. Any real truth to this
> > statement?
> >
> >
> >
> > Thanks, Jim
> >
> >
> >
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> >
> >
>
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