More Fan Comments

[Steve Ellington]

I'm hearing a lot about fan noise in the Centaur amp. Probably there is
a general misunderstanding amonst us on proper cooling for large tubes. 
I had a Ameritron AL-80b here for a while. The fan was positioned so as
to blow horizontally across the 3-500z. Although it was very quite as
advertised, I feel it was inadaquate and as a result, short tube life
could be expected.

Fans need to keep air blowing evenly across as much surface area of the
tube as possible. More expensive amps have glass surroundings for the
tube which conduct air like a wind tunnel around it. The fan is mounted
underneath the tunnel. This requires an expensive tube socket, chimney
and plenty of room all of which increase the cost of the amplifier.
Expect to pay over $2k for these amps.

The Collins 30L-1 used four 811 tubes and the fan looks like something
from a record player motor. The cabinet gets hot enough to fry eggs on.
But it was quite! 

The quitest fans are squirrel cage blowers. They can move lots of air
for  their size. The problems with them is usually space. They need to
be mounted externally and ducting is required to direct the air to the
tube's chimney. They aren't cheap either. 

I've seen the Centaur amp but never heard one. I suspect that TenTec
used a fan large enough to keep the bottles cool.....period. This amp is
a low cost job so don't expect too much. It's a trade off. If you want
long tube life and low cost, you get noisey fans. For short tube life,
you get a quite fan. For long tube life, high power, cool cabinet and
quite operation, you must pay $$$$.

I'm certainly not a fan expert but generally, the higher the cfm of a
muffin fan, the louder it is. Those little fans in the import rigs ie.
TS, FT, IC et al. produce very little cfm. In fact, hold your hand over
one and feel the air blowing. They just gently move the air out of the
cabinet. These shouldn't be compared with fans in tube type amplifiers.

Could TenTec have made the Centaur quieter? I don't know but maybe I hit
on some reasons why. I think the main one is cost. 

N4LQ Steve

--
FAQ on WWW:               http://www.contesting.com/TenTecFAQ.html
Submissions:              tentec@contesting.com
Administrative requests:  tentec-REQUEST@contesting.com
Problems:                 w9tw@contesting.com
Sponsored by:             Akorn Access, Inc & N4VJ / K4AAA