[Amps] Centurion cooling improvement ideas for AM service

[R.Measures]

-  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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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org