----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@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@yahoo.com>
> Subject: Re: [Amps] Tube Cooling..
>
> ORIGINAL MESSAGE:
>
> On Tue, 23 Nov 2010 20:28:52 +0000 (GMT), DAVE WHITE
> <mausoptik@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
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