[Amps] QRO Heat management

[Rob Atkinson]

Heat can be an issue with some ham amps built over the past 30 or 40
years (can't say that about all of them since I have not owned all of
them).  There are several reasons for this.   When SSB became the
popular voice mode, designers realized they could come up with amps
that would work okay for most users operating ssb and cw (duty cycles
of no more than 50%) because most transmissions were no longer than a
few minutes.   They could build amps with lighter power supplies, make
them compact and relatively light weight to sit on a table top, and
pass the lower costs on to the customers.

These amps were cooled adequately, but some hams complained about
noisy fans.   Now we have some ham amps with whisper quiet fans to
make these users happy.  I've seen amps advertised and reviewed
positively for being quiet.   They work okay for the above described
operation such as a typical ssb ragchew where no transmission is
longer than 5 minutes but if you run RTTY or heaven forbid AM, with
one it will darn near melt down pretty quickly.   Another practice
that I think Dentron among others got into, was to try to cram as much
as possible into the smallest cabinet possible, which never made sense
to me, but maybe some users thought a compact amp was a good thing.

So anyway, there's nothing wrong with augmenting the cooling and in
fact you may have to if you have one of these desktop "quiet" amps and
you want to run slow scan or make long transmissions on cw.  In my
opinion the trick is to not have the added fans somehow obstruct
airflow rather than increase it.  The goal should always be moving air
in and out of the cabinet.   If the chamber to be cooled is sealed,
you have to be sure the amount of air at any instant being pushed in,
is the same amount as that being sucked out, otherwise a fan is going
to be worked against or pushed.    This is usually an easy problem to
fix by adding some vent holes, or having all fans blowing in or
drawing out.  The best amps have big cabinets with lots of space
around all the components.   I think these days, if you want an amp
like that you have to build it yourself.

73

rob / k5uj