Hi Bryan,
Tnx for your helpful comments. The various data sheets for the GU74B/4CX800A
are not entirely consistent, but the numbers are in the ballpark to those
you mentioned. With a three-tube amplifier at 5000ft (my QTH is actually
7000ft) I think the EBM blower is barely adequate for 1800W dissipation at
25C. At 50C, I would need 65cfm but the blower can only deliver 31cfm at
the required back presure. I could probably get away with it, given the
lower duty cycle of CW and SSB, but I'd rather have a larger safety margin.
Guess I'll have to find another blower. It's a shame, because this one is
the perfect size for me.
nfortunately, I can't use your temp-sensitive lacquer suggestion, because
I'm building the enclosure specifically for the blower I'll use and I don't
have a lot of room. Once the enclosure is completed, I'd have to rebuild the
enclosure to swap in blowers of a different size.
73,
Jim W8ZR
> -----Original Message-----
> From: Bryan Swadener [mailto:bswadener@yahoo.com]
> Sent: Saturday, March 23, 2013 1:36 AM
> To: 4cx250b@miamioh.edu
> Subject: Re: Blower Question
>
> Hi Jim,
>
> According to the GU74b datasheet (http://www.nd2x.net/gu74b.html), it can
dissipate up to
> 600W with a maximum anode temperature of 200°C. The latter number is key.
The
> datasheet graphs show that, at 600W dissipation, it needs 25 to 55 m^3
(cubic meters/hour)
> airflow depending on the air temperature. In "American units", that's
14.7 to 32.4 cfm.
>
> According to the EBM-Papst G2E085 datasheet
> (http://www.ebmpapst.us/allpdfs/G2E085.PDF), there's no blower with the
exact part
> number "G2E085-05-10" (the last two numbers are different). It MAY have
plenty of
> capacity or just barely not enough.
>
> I would then suggest running the blower while monitoring anode
temperature. Use one of
> the temperature indicating labels, crayons, or lacquers from Omega
> (http://www.omega.com/), or an IR temperature "gun". Harbor Freight has
one that's
> inexpensive.
>
> vy 73,
> Bryan WA7PRC
>
> > Date: Thu, 21 Mar 2013 20:23:44 -0600
> > From: "Jim Garland" <4cx250b@miamioh.edu>
> >
> > Hi All,
> >
> > I've been rummaging through my box of fans and blowers,
> > looking for a
> > compact blower to power three GU74-B tetrodes. I've got a
> > cute little EBM
> > blower, marked G2E085-AA05-10, which I believe came from an
> > ETO MRI
> > amplifier, but don't recall what tubes it was used for..I
> > can't find any
> > specs on the blower and wonder if anybody can help me out?
> > It's small,
> > German-made. cast aluminum body, with a pancake-type motor
> > that uses a 4uF
> > start capacitor. It's rated at 115V/60Hz and 28W. I've got a
> > 230V version of
> > the blower as well, but for this application want to use the
> > 115V version.
> > I've got several larger blowers, but I want to make this a
> > relatively
> > compact amplifier.
> >
> > Tnx and 73,
> >
> > Jim W8ZR
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