[Amps] MLA2500 issue

[Steve Thompson]

What happens to the HV, grid current and plate current during 
these changes?

Steve

> 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?
>
>
>
> Thanks
>
>
>
> Mike VE9AA
>
>
>
> Mike, Coreen & Corey
>
> Keswick Ridge, NB