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Re: [Amps] MLA2500 issue

Subject: Re: [Amps] MLA2500 issue
From: Steve Thompson <>
Date: Tue, 15 Nov 2016 07:51:02 +0000
List-post: <">>
What happens to the HV, grid current and plate current during these changes?


Hi All,

I'm no amp expert, but have owned an MLA2500 for close to 3 decades.  I've
repaired it a few times (all new caps, timer tube replaced, PS board
replaced one time). Might have put in a new tube once.

I use it for contesting. I've used it on DXpeditions back in the day, so
it's sees LOTS of use.

When I am on CW, I always operate it in the lower plate voltage mode.

Recently in a contest I started experiencing sudden/rapid power output loss,
from its usual 750w CW to perhaps 300w for some minutes, then briefly 100w,
then within several minutes, no output at all. If I shut it off and restart
it 20-30 minutes later from cold(warm?) I usually sees perhaps 300-400w out
for a couple minutes, dropping to 100w within a minute,then 0 (or
essentially 0) watts out.

It's just getting worse.

When I took the cover off, it appears one of the 8874's is much darker than
the other. This might be nothing, as I have had various 8874's from
different sources over the years, but thought I'd mention it in case it
means something


Looked around and measured continuity with the ohmmeter here and there. Not
seeing anything obvious.

Is it a bad tube?

Where would I start troubleshooting?


Mike VE9AA

Mike, Coreen & Corey

Keswick Ridge, NB

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