- In the 21st century, the best way to determine if seal cooling is
adequate is with an IR digital thermometer. If I spring for one, it
will be a Fluke. With a name like that, it has to be pretty well
engineered.
On Aug 25, 2004, at 4:51 AM, Ed Briggs wrote:
I contacted the manufacturer on a related topic some time back. Their
official response (contained in the manual) is for keydown operation,
650W
max, 50% duty cycle, 10 minutes max transmission time (as you know
from the
manual)
I inquired how to derate this for a longer transmission time (say 30
minutes). I speculated that since when operating bias is applied (no
rf
drive) the amp idles at appx 160 ma yielding a dissipation of 450w,
representing just under 50% of the combined dissipation of the two
tubes,
and I asked, is it 'safe' to let the two tubes run with at this level
of
dissipation for 30 minutes (the key is up after all).
They responded " In theory 450 watts should be safe for key down
operation
but we could not guarantee the tubes would survive this operation."
How does this apply to your AM question. The manufacturer seems to
have
some reservations about cooling at 450w steady state so, although I'm
not
sure whether they mean 450 w output or 450 w dissipation (possibly the
same).
Others on this reflector may be able to use this data point from the
manufacturer to predict.
Ed
----- Original Message -----
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
To: <amps@contesting.com>
Sent: Tuesday, August 24, 2004 10:13 AM
Subject: [Amps] Centurion cooling improvement ideas for AM service
Hi folks,
I am the owner of a 3 year old Ten Tec Centurion amp. This unit
employs
two
3-500ZGs on an elevated socket platform in the rear right side of the
cabinet (when facing the front panel). On the rear left side is the
h.v.
power supply with a Dahl model 422 transformer which delivers 3.2 kv
(around
2.9 under load) to the plates. Between the p.s. and rf deck is a rf
shield
running down the middle of the chassis. A square hole is cut in this
between the tubes and p.s. and over that is mounted a Bi-Sonic tube
axial
muffin fan, model 4E-115-S21, sleeve bearing, 115 v. 220 ma 20 w.
2200 RPM
moving 82 CFM. The fan is on the tube side of the shield, and draws
air
in
through the left side of the cabinet, over the p.s. and exhausts it
horizontally over the h.v. plate choke and tubes, including the pins
and
anode heat sinks, which are the flat type extending out horizontally.
As
most of you know, this has become the standard cooling method for
these
tubes in amateur amps since Heathkit began using it for the SB220.
This cooling is adequate for low duty cycle modes for which the
Centurion
was designed, but I would like to use mine for brief transmissions (5
to
10
minutes or less) of dsb carrier AM running a carrier of 200 to 250
watts.
I
have done this for a couple of minutes and the amp gets pretty darn
hot.
I
would therefore like to boost cooling so as to avoid seal failure.
Increased noise is not a problem for me.
Bi-Sonic manufactures a fan that is identical to the stock fan but at
higher
rpm, and 20 more ma, 22 w. and 105 CFM, around a 25% improvement over
stock.
Is this an increase worth pursuing? Another possibility would be
to add
a
fan to the external surface of the cabinet over the grill on the right
side
of the rf deck to speed up the draw of air to the right, out of the
cabinet.
Again, is this an improvement, and would it be worth pursuing?
Overall, :
A. Are these mods necessary
B. Are there any comments on these methods
C. Perhaps most important, is operating this amp on AM beyond its
efficiency
and heat dissipation design capability and should I keep it for SSB
and
CW,
and look for something with higher plate voltage and/or tubes with
higher
plate dissipation / more cooling?
Tnx,
Rob Atkinson
K5UJ
p.s. to save you time and trouble, please no comments to run a plate
modulated boat anchor.
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