[1000mp] Very Hot Final Heatsinks

[Rick Moskovits]

Hans, can the mkv field be operated in class A safley?- I have not done this
and now i am quite concerned- any help with your experience on this would be
most appreciated!
vy 73, Rick-VE1RNM

Hans Remeeus wrote:

> Class-A uses a constant current. This constant current is important for
> a lower TX distortion. When you decrease the power output from 75 to
> e.g. 25 Watts this has to be absorbed by the heat sink. So the heatsink
> has two jobs: handle the constant (HIGH) current and handle the
> absorbtions of the 50 Watts in less power output. This is too much for
> the finals. When an amplifier is operated in Class A, it will be hottest
> at zero output power, because all of the DC power input will be
> converted to heat.
>
> This is the main reason why I sold my Mark-V 200 and bought the Mark-V
> Field with 25 Watts Class-A, which is a very good power input for my
> linear amplifier Acom 2000A. It then gives 800 Watt power output, which
> in most situations is more than enough.
>
> To be honest; who ever will notice that you are transmitting in Class-A
> instead of Class-AB...? IMHO Class-A is nice to have, but not need to have.
>
> 73,
> Hans Remeeus (PA1HR)
> http://www.remeeus.nl
> Communication is about people, the rest is technology.
>
> William Shadid schreef:
> > Norm,
> >
> > Hans is correct. I long ago learned this with my Mark V -- leave the
> > power
> > level at maximum on Class A. I note a higher temperature level in Class A
> > but nothing like what I hear about on the reflectors. Up to now I had
> > thought this to be a problem with selected radios -- but Hans' note
> > gets me
> > to thinking that it is really a lack of understanding with the radio.
> > Yaesu
> > should be more clear about this -- but they certainly do not have an
> > edge on
> > things omitted from the manual!!
> >
> > I drive an older Drake L-7 with my Mark V and use the Class A selection
> > simply to keep my drive power low. I do not use Class A when I run PSK.
> > While I don't often run the amplifier, I can say that I note only
> > somewhat
> > higher heat sink temperatures. The fins are far cooler than running older
> > domestic, solid state radios such as an old Cubic Astro 103 with its
> > large
> > rear heat sink. They are also much cooler than the single heat sink on my
> > Ten-Tec Omni VI+ after a long operating session. If you are experiencing
> > "scalding" temperatures at 75 watts output, Class A, I would say that
> > a call
> > to Yaesu is in order.
> >
> > 73,
> >
> > -Bill, WA9MXQ
> >
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