Ian et al.
I'm running a single GI7bt (the ruggedized version) on 144MHz with 400W+ out
on SSB and running extensively WSJT (30s on 30s off 100% output) with 300W
out, using only an 18W muffin for cooling!
No change to the anode cooler, and using the "flowerpot" trick for
concentrating the airflow.
See my homepage for details....
Vy 73 de OZ1PIF, Peter
********** OZ1PIF **************
email: oz1pif(no-spam-filler)@get2net.dk
http://hjem.get2net.dk/oz1pif
Ph. +45 4619 3219
Snailmail:
Peter Frenning
Ternevej 23
DK-4130 Viby Sj.
Denmark
***********************************
----- Original Message -----
From: "Ian White, G3SEK" <G3SEK@ifwtech.com>
To: <amps@contesting.com>
Sent: Thursday, November 15, 2001 11:26 PM
Subject: Re: [AMPS] Gi7B Tube Amps
>
> Douglas R Snowden wrote:
> >
> >Tore Sandström wrote:
> >
> >> Ask W4EMF (w4emf@bellsouth.net)! He is installing 3 x GI7b in a Drake
L4B amp. Hes friend, KV4H Danny, is converting a MLA-2500 to 2 x GI7b. He
> >>has already coverted the MLA1200 to one GI7b. Danny has removed the
original heatsink and installed fins so he can use a muffin fan from a PC.
>
> >How does the original heatsink come off? Glue? Screws?
> >
> One big slotted nut, leaving a round flat surface and a threaded post.
> The original anode cooler is sand-cast, with a relatively small number
> of fins, so it really isn't very effective and transferring the heat out
> to the air-stream.
>
> Once upon I time, I thought of replacing it with a much more efficient
> anode cooler from a dead Eimac tube (4CX250 or larger) and making an
> adaptor piece from solid copper... but I never got around to it.
>
> However, I doubt that a muffin fan would be suitable for cooling any
> "external anode" tube unless you use *really* big fins with a minimal
> pressure drop. Muffin fans are very good for moving large volumes of air
> where there is no flow restriction, but they are not good at forcing air
> through the small gaps in a typical finned anode cooler. For that you
> need a centrifugal (squirrel-cage) blower.
>
> People who use the GI-7b for 1296MHz generally change to water-cooling,
> using a water jacket that slips over the threaded post and makes good
> contact with the flat surface.
>
> --
> 73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.com/g3sek
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/amps
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> Problems: owner-amps@contesting.com
>
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