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Re: [Amps] MLA-2500

To: amps@contesting.com
Subject: Re: [Amps] MLA-2500
From: Kimberly Elmore <cw_de_n5op@sbcglobal.net>
Date: Fri, 25 Jan 2008 09:01:57 -0800 (PST)
List-post: <mailto:amps@contesting.com>
My Dad had an MLA-2500. I recall that we had to add some fixed C-load for it to 
load properly on 160 m; even at that, it didn't do well below about 1.85 MHz or 
so. It was also not very efficient on 10 m because the output tank had a loaded 
Q that was too high. Never tried it on 12 or 17 m. But, other than that, it 
seemed to be a fine, very compact amp. Made about 600-700 W output, if I 
recall. His had the original tubes (made, apparently, of unobtainium) in it and 
saw service only on 75 m and (mostly) 40 m SSB.  I don't think the efficiency 
was particularly noteworthy. Prior to my Dad becoming an SK, I replaced the 
filter caps in the HV PS after the originals became leaky. That was a bit of a 
job... Unlike my AL-80A, I also recall that it would only tune properly with 
the covers on and secured. 

73,

Kim Elmore N5OP


At 11:01 AM 1/25/2008, n4zed@comcast.net wrote:
>I suspect something is wrong also but I think it is in the design and
 not 
>in any particular component failure. I've done the usual Google search
 and 
>found the loading problem is common with this amp.  During the search
 I 
>have found no fixes to the problem.
>
>This amp had never been powered up when I got it about 3 months ago..
 The 
>power cable had never been connected to a plug and the tubes were
 still in 
>the original boxes from Eimac. The relay contacts as far as I could
 tell 
>had never been energized and showed no sighs  of any electrical
 contact at 
>the contacts(that sounded weird), none of the connectors on the rear
 had 
>any sigh of a connector being screwed on or pushed on.
>
>There are places on the web that covers a gold sputtering problem with
 the 
>2500 and the 8875 tubes due to VHF parasitics and other high Mu tubes
 for 
>that matter.
>
>There are others that say they have ran their 2500 for 20 years and
 had no 
>problems.
>
>The amp works fine, good output, good reports. So why fix something
 thats 
>not broken right? I just want to keep it that way, the tubes are way
 too 
>expensive to replace.  One good thing about buying something that has
 been 
>out in the field a long time is that you get to see what kinds of
 problems 
>there were with the design and hopefully fix it before it hits you in
 the 
>wallet or something very close to the wallet.
>
>Ken
>
>*************************************************************************
>
>
>
>Somethings definitely wrong then.
>
>Id start by closely inspecting the bandswitch and plate choke.
>
>BTW, the cover has to be in place when tuning, the steel that close to
 the
>coil has a huge effect.
>
>Carl
>KM1H
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