Hi Jim,
The fan noise is why I traded my Centaur in on a Centurion amp. The
Centaur does an excellent job, otherwise. (and the Centurion looks so
pretty next to the VI+!)
I did not perform the surgery on mine, but I can tell what my
"alternate" plan was. You will find if you remove the case that the fan
makes very little noise. But hold anything in front of the fan input
(use a Mouser backscratcher !) and you will hear the beginnings of the
noise. According to an acoustic/thermal engineer at my place of
employment who looked at it, TT simply mounted the fan too close to an
obstruction (cabinet side) such that there is turbulence generated at the
leading edge of the fan blades, and that is where the noise is generated.
This engineer recommended starting with punching round holes in the side
of the case in the fan intake area. If that didn't provide enough noise
abatement, he recommended removing all the case material at the fan
intake (and I would add, cover it with one of the kits available in
Newark to filter the air and keep fingers and other large objects from
finding their way into the fan or the case.) This was not a tested fix,
but this guy has a lot of experience on cooling fan noise problems, and,
as I mentioned, removing the case will almost totally eliminate the
noise.
I think there were two reasons they used the 100 CFM fan - they had to
adequately cool the third 811A in the lineup, and it provided them some
"oneupsmanship" over the competitors' amps, some of which are a bit
undercooled. And, you're right, the switches could be a little
gutsier...
73, Duane AC5AA
On Sat, 09 Sep 2000 13:09:47 -0500 James Parsons <k5rov@wcc.net> writes:
>
> Hi, Gang...
>
> I have a Centaur amplifier that I bought new from TT some years ago.
> It
> has been a faithful performer (except for those cheap switches), but
> it
> sure does suffer from high fan noise. It seems that 100 CFM is a lot
> of
> air to move across those tubes. I built a lot of amplifiers during
> my 58
> years of hamming, and a number of them were 811 type, but I never
> blew
> that much air across them.
>
> I wonder if anyone has replaced the fan with a slower one, or maybe
> put
> a series resistor in the line with the existing fan? I need to do
> something because the constant blower noise over a period of
> operating
> hours is sure tiring. It seems my options are:
>
> 1. Replace the fan with a slower one (will the tubes get too warm?)
> 2. Slow the fan down.(how many CFM?)
> 3. Disconnect the fan and use some muffin fans on the top of the
> cabinet, blowing towards the tubes.
> 4. Replace the 811 tubes with 572B tubes and much less cooling.
>
> I have found that changing the mounting of the fan, as some have
> suggested, has not worked.
>
> Has anybody done anything about this? I have never figured out why
> TT
> found a need for 100 CFM for 811 tubes unless it is the way the fan
> had
> to be mounted and the fact that the tubes are in a line of three in
> a
> horizontal plane with the fan.
>
> I would like to hear from anyone who has ACTUALLY made a
> modification to
> this amplifier for this purpose.
>
> Thanks and 73 de Jim, K5ROV
> --
> James (Jim) Parsons, K5ROV USAF, Ret. Ham for 58 yrs.
> k5rov@wcc.net QCWA, ARCI, Fists, ARRL, ARMS
> EX: W1RLA, K5FBB, K4FEO, SV0WN (CRETE), SV0WN (RHODES),
> DL4NC, DL4JP, KA2FC (JAPAN), KA2JP (JAPAN).
> JOHN 3:16
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/tentec
> Submissions: tentec@contesting.com
> Administrative requests: tentec-REQUEST@contesting.com
> Problems: owner-tentec@contesting.com
>
Duane A. Calvin, AC5AA
Austin, Texas
ac5aa@juno.com -or- ac5aa@earthlink.net
Day: dacalvin@us.ibm.com
--
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