Have you run the amp into a 50-ohm dummy load? It really doesn't make sense
to me that the load cap would be near minimum (or maximum) capacitance into
a 50-ohm load on all bands.
As for gold sputtering, let's not go there - that's one guy's crusade,
which has long since gone beyond engineering into personalities and
historic grievances.
73, Pete N4ZR
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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