Re: [Amps] Cooling requirements GS35B

[R.Measures <r@somis.org>]

On Feb 10, 2005, at 5:15 AM, Tony King - W4ZT wrote:

> Hi Robert,
>
> The air flow of 90 cfm is published but I haven't seen any reference 
> to back pressure in any documents anywhere. Back pressure depends on 
> the capacity of your blower and if you achieve the 90 cfm, the back 
> pressure shouldn't matter except maybe to your blower.

Back-presure is proportional to cfm.

> More air is better to the point it blows the tube out!  It's been 
> suggested before to use a large plastic garbage bag drawn tightly over 
> the top of the tube to do a rough estimate of the airflow from  your 
> blower through your tube.

Another method is to use an IR thermometer to see if the ceramic-metal 
seals are in danger.  SSB-cooling takes a lot less air than 
RTTY-cooling.

> Roughly estimate the volume of the bag and then measure the time to 
> fill it. If you can measure (roughly) 90 cfm or more through the tube, 
> then you're getting the rated cooling. You can measure back pressure 
> with a plastic tube and a column of water if it is important to you.
>
> I'd like to add that the BOTTOM of the GS-35B including the grid ring 
> will get VERY hot with nothing but filament voltage on the tube so it 
> is very important to keep air flowing even with no anode voltage 
> applied. In fact, it will get too hot to hold in your hand if you 
> don't put significant air around the base. Be sure that your grid ring 
> is firmly clamped to a metal plate (thicker is better) to help 
> dissipate the heat. You've got about 38 watts from the filament plus 
> the grid dissipation to deal with.
>
> I've got a collection of GS-35B info on my web page: 
> <http://amp.w4zt.com>
>
> 73, Tony W4ZT
>
> Robert Thain wrote:
> > Hi I'm looking for the cooling requirements for a GS35B.
> > I understand that flow rate AND back pressure are
> > important and usually quoted. But I just cant find
> > this info.
> > If I understand correctly:
> > Flow rate equates to the volume of air needed
> > and back pressure equates to the force of the air
> > needed.
> > Thanks
> > Robert
> > G0HGW@yahoo.com
>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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