[Amps] Tube Cooling..

[Jim Thomson]

Date: Wed, 24 Nov 2010 21:52:30 -0800
From: "Bill, W6WRT" <dezrat1242 at yahoo.com>
Subject: Re: [Amps] Tube Cooling..

ORIGINAL MESSAGE:

On Tue, 23 Nov 2010 20:28:52 +0000 (GMT), DAVE WHITE
<mausoptik at btinternet.com> wrote:

> Whilst it may seem counter-intuitive to blow cooling air DOWNwards I've seen tome successful Eastern European designs whereby large fans blow air directly downward onto the top of the tubes so that the air runs by the fins.

REPLY:

The trouble with that approach is you have hot air blowing down over the
tube seals and socket. Not good. Anodes by themselves are relatively
unaffected to heat compared to the seals and socket. 

Better to have the cool incoming air flow over the socket and seals
first and then go to the anode. 

73, Bill W6WRT

##  partially agreed.   On any Eimac spec sheet, they will  always depict  both top down cooling, and bottom up cooling. 
With top down cooling, way more CFM is required.  Also, a separate air hose must be used to cool the coaxial fil stem
on some tubes like 3x3 and 3x6, etc.   It's those fil seals  that will get you every time with top down cooling.  The normal
deal with the 3x3 and 3x6, when using top down cooling is.... 5-10 cfm  must be directed at the coaxial fil.   Top down
cooling will  work, but wouldn't be my 1st choice.   

##  You also have to be careful when using muffin  fans,  and using em to suck hot air out !   Papst  used to make
many of their 3/4/6"  diam fans in two versions,  sleeve bearings and  ball bearings. [ they all appear to be ball bearing
only these days].    The ball bearing versions  would handle a lot more heat than the sleeve bearing version.
85 deg C  VS  55 deg C.     55 deg C is not that much .......=  131 deg F.    [85 deg C =  185 deg F] 

## depending on how hot the exhaust  air gets,  you could shorten the life of a sleeve bearing fan  very quickly. 

later... Jim   VE7RF