What many also forget or are too young to realize is that many of the
older amps were built when the power was FCC regulated as 1000W CW and
2000W PEP SSB INPUT. Those full legal power amps had a CW/SSB switch for
that reason and I guess a few hams actually used them (;
When run at full bore of 1200-1800W OUTPUT on CW the duty cycle warms
things up a bit more than at the old limit which is roughly 600-700W
output.
Wassamatter with AM? Properly adjusted 1500W output linears work fine at
375W carrier which is 1500W PEP. Thats easier on them than RTTY and if
using controlled carrier AM its even lighter duty. A DX-60 with some
audio mods sounds great with a SB-220.
Carl
KM1H
----- Original Message -----
From: "Rob Atkinson" <ranchorobbo@gmail.com>
To: <amps@contesting.com>
Sent: Monday, November 10, 2008 12:36 PM
Subject: [Amps] QRO Heat management
> 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
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