I should have added to my post that, when tuned into a 50 ohm resistive
load, I never saw the kind of behavior reported here with the load
cap. It pretty much tuned by the book. Something isn't right with yours as
this simply isn't normal. And, I'll also add that I never, ever
observed any sign of parasitics of any kind in the amp. I recall that it was
touchy about tuning, and had a narrow output impedance range that it
could accommodate. Overall, a fine amp.
Kim Elmore, N5OP
----- Original Message ----
From: Kimberly Elmore <cw_de_n5op@sbcglobal.net>
To: amps@contesting.com
Sent: Friday, January 25, 2008 11:01:57 AM
Subject: Re: [Amps] MLA-2500
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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