[Amps] Centurion cooling improvement ideas for AM service

[Rob Atkinson, K5UJ]

I did not even know about these.  How much are they?  If they are
designed to connect by wire to a sensor that can be placed in the
rf deck area it might be worth it to have one dedicated to monitoring
the temp.

Rob/K5UJ


From: R. Measures <r at somis.org>
To: Ed Briggs <edbriggs at optonline.net>
CC: "Rob Atkinson, K5UJ" <k5uj at hotmail.com>, amps at contesting.com
Subject: Re: [Amps] Centurion cooling improvement ideas for AM service
Date: Wed, 25 Aug 2004 07:01:07 -0700

-  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 at hotmail.com>
>To: <amps at 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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>
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>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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