Late last year I was complaining that the fan in my L-4B was not keeping
the valves within their temperature rating with 50Hz mains, especially
on CW at full power. Jason N1SU suggested that I replace the stock fan
with a Dayton 4C761. I finally got one of these units brought over to
the UK by a work colleague.
I just wanted to report that the fan is pretty much a straight swap. I
had to saw and grind off the exit flange on the blower and extend the
through hole in the chassis to accept the bigger outlet. The intake does
not quite line up with the original hole on the rear panel of the
amplifier because the new blower is slightly bigger. The error is not
large - the escutcheon fits OK without fouling - and anyway it's out of
sight at the rear of the case.
I used 1.5mm felt from a craft store as a sound deadening gasket at all
points where the blower meets the chassis. Even so, the Dayton blower is
noticeably noisy, as Vic K2VCO predicted. I find it acceptable, because
I operate mostly on CW with headphones. On SSB, with the speech
processor turned on and the L-4B 18 inches from me, the fan noise drives
my transceiver to about 10% output. It would be even worse on 60Hz mains
unless steps were taken to slow the fan motor down. Much of the noise is
coming from the impeller and a clip-on external dust filter of the type
sold for muffin fans might be worth investigating.
Has it fixed the overheating problem? Oh yes, definitely. I can feel a
healthy breeze from the top of the cabinet and the case is now only
comfortably warm to the touch at the end of a long transmission.
I have photos I can share with anyone who is contemplating this mod.
Thanks to everyone for their suggestions and encouragement. I'm very
happy with the outcome.
--
Cheers,
Alan G3XAQ
alan@g3xaq.demon.co.uk
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