[1000mp] Very Hot Final Heatsinks

[Hans Remeeus]

The Class-A is a very nice marketing instrument to up-value the Mark-V. 
I don't think this was necessary, as the price/quality-relation of the 
Mark-V is one of the highest on the market.

If Class-A really should be a 'need-to-have' feature, then other brands 
would have implemented this in their rigs as well. They did'nt...

Reducing the power will not cause any problem while running Class-AB on 
the Mark-V .

When driving Class-A; always do this at the highest power output! Never 
reduce power. Yaesu should have writting this as warning in the 
operating manuals of the Mark-V series.

73,
Hans Remeeus (PA1HR)
http://www.remeeus.nl
Communication is about people, the rest is technology.




Rob Atkinson schreef:
> i stay out of class A entirely.   i heard a new PA costs $700 in the 
> u.s.  for the 200 w. version.   i almost fried mine anyway one time 
> when i put the cover back on and the speaker leads obstructed the fan 
> and kept it from turning.   just by luck i touched the heat sink after 
> about 15 or 20 minutes and was it ever hot!   pulled the cover off and 
> saw the speaker wires down in the fan.   after that close call, plus 
> hearing over the past year or so, all the stories about class A doing 
> in the PA, I stay on AB.   If in AB ur heat sink still gets too hot, 
> I'd just aim a second (external) fan down on it.
>
> with the increased popularity of high duty cycle modes, plus a renewed 
> interest in AM, the finals on rigs are getting a workout they did not 
> receive back in the days when a transceiver was made to do ssb and 
> cw.    i wish manufacturers could make the new rigs more like ccs 
> transmitters, but i guess the cost would by sky high.
>
> rob / k5uj
>
>
>
> On Monday, November 28, 2005, at 03:16 PM, 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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