[Amps] Centurion cooling improvement ideas for AM service

[Rob Atkinson, K5UJ]

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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