On Sat, 20 Mar 1999 12:41:01 +1300 Martin Ellis <jmellis@ihug.co.nz>
writes:
>
>Vic, K2VCO wrote:
>>> One more question: may I get your opinions on cooling
>>> 3-500Z's? Is it better to use chimneys and a pressurized
>>> chassis, or the 'sb-220 method' with a muffin fan blowing
>>> across the tubes?
>
> Carl KM1H replied:
>> The 220 method works well as long as you direct some air
>> at the socket pins. The Harbach fan makes this an
>> attractive ( cheap) option to chimneys. You could also use a
>> muffin fan if you are careful in the selection and positioning.
>
>The amplifier that seems to run cool and quiet is the KW TL922.
>This uses a fan on the rear of the cabinet. It does not blow air
>across the tubes. The fan is mounted directly behind the
>2x 3-500z tubes, and extracts air from the cabinet. The cabinet
>needs to be several inches from a wall to allow the heated air to
>disperse.
>After 2 days contesting on SSB, the top on the TL922
>cabinet is still at room temperature.
>In comparison,
>the top cover of a 2KD-5 was hot enough to fry eggs.
>
>Martin ZL1ANJ
Good point Martin. The TL-922 runs cool but at the expense of a rather
elaborate and complicated series of panels and baffles.
Of course with Rich's relay mod plus replacing L-2 with a glitch resistor
and adjusting the filament voltage, there should be very long intervals
between removing a zillion screws to service.
My LK-500 uses a fan and after 13 years I have not had any cooling
problems even during 2500 QSO contest weekends.
73 Carl KM1H
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