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Re: [Amps] mounting (UHF) RF powermodules

To: "Steve Thompson" <>, <>
Subject: Re: [Amps] mounting (UHF) RF powermodules
From: "jeremy-ca" <>
Date: Tue, 25 Mar 2008 08:41:49 -0400
List-post: <">>
Several years ago one of the commercial customers on my tower was having 
steady failures with a new UHF amp. After the 3rd set of finals he asked me 
if I had any ideas.

The heatsink was about 17" x 12" and you see where this is leading. He 
removed it and I could see even by eye that it wasnt straight.

Down it went to my local machine shop who was doing the work on my race 
motors for over 20 years and up onto the head milling machine. I wanted an 
almost mirror finish so he made 4 passes. If I remember he took off almost 

Put the amp back in service ands its been steady ever since.


----- Original Message ----- 
From: "Steve Thompson" <>
To: <>
Sent: Tuesday, March 25, 2008 4:08 AM
Subject: Re: [Amps] mounting (UHF) RF powermodules

>>>Expanding on those, any heatsink you buy will not
>>> be flat enough without machining, ideally with a large diameter
>>> 'fly' cutter. You are also looking for a good surface finish with
>>> machining ridges barely detectable with a fingernail. As well as
>>> flat (50um or .001" over the module area) clean is important.<
>> Not sure that I would agree about a fly cutter. Better than nothing, but 
>> I
>> would prefer
>> a horizontal milling cutter. Alternatively, a face-and-end milling 
>> cutter.
>> A large slot drill
>> might give a good enough finish.
>> Another good way would be to use a shaping machine.
> The choice probably varies with the machinery available. Up to 6"
> wide I get things skimmed on a single pass and they give me a low
> roughness finish. With end cutters or slot drills the finish is
> usually excellent but there can be a tendency for tiny
> steps/ridges between passes - I've learnt to specify that any
> mounting area must be cut in a single pass.
> Steve
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