[Amps] Tube Cooling..

[Carl]

----- Original Message ----- 
From: "Jim Thomson" <jim.thom at telus.net>
To: <amps at contesting.com>
Sent: Thursday, November 25, 2010 11:47 PM
Subject: [Amps] Tube Cooling..


> 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

Top down cooling is the norm in many coaxial cavities at VHF/UHF. My Collins 
432 MHz military amp with a 2.75KW dissipation tetrode runs that way and it 
was used as an AM linear at 1000W out. A seperate small blower cools the 
input side. Due to the TX/RX relay and the coax going to the hardline and 
antennas I cant run it even close to its capabilities.

I'll also be using that method at 1296 with a pair of  GI-7B's unless I 
decide to go with water cooling.

Carl
KM1H