Re: [Amps] MLA2500 issue

[Clark Turner <Clark@ClarkTurnerTuning.com>]

Another long shot:  I had a MLA2500 that would also lose power when 
warm. After wasting hours trying to diagnose the amp, I unhooked it and 
realized the problem. The factory antenna output jack was worn out and 
would not make contact to the center pin. For lack of a better term the 
connector was "whored" out. I attempted to bend the fingers back in and 
that immediately snapped one off. I replaced the connector.
C


On 11/15/2016 4:20 PM, Alek Petkovic wrote:
> If there's no smoke, it could be the input capacitor/s to the cathode, 
> going bad as the temperature rises. That happens quite a lot on the 
> older Yaesu amplifiers except they usually fail completely open circuit.
> I notice in the 2500, there are 2 capacitors in parallel. A long shot 
> would be that one of the capacitors goes open and then the other 
> succumbs to the extra strain.
> Just my shot in the dark.
>
> 73 and good luck.
> Alek. VK6APK.
>
> On 15/11/2016 8:34 PM, Jim Thomson wrote:
> > Date: Mon, 14 Nov 2016 17:07:15 -0400
> > From: "Mike Smith VE9AA"<ve9aa@nbnet.nb.ca>
> > To:<amps@contesting.com>
> > Subject: [Amps] MLA2500 issue
> >
> > 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
> >
> > ## Can u run the amp with one tube removed ?   Its probably one or 
> > both tubes.
> > Run it with one tube at a time.  You can also swap positions in case 
> > its a socket issue.
> > Do you have any spare tubes ?   Does it do this on all bands or just 
> > one band ?
> > Jim   VE7RF
> >
> >
> >
> >
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