[Amps] Dentron MLA2500 SWR Problem

[Carl]

You havent stated what value choke you used. Or what examination and 
testing has showed.

Carl
KM1H






----- Original Message ----- 
From: "Adrian Rees" <rees.a at btconnect.com>
To: <amps at contesting.com>
Sent: Tuesday, August 12, 2008 3:05 AM
Subject: [Amps] Dentron MLA2500 SWR Problem


> Hi all
>
> Just an update to my previous emails.
>
> Last night I completed the modifications suggested by the late Chris 
> Lund. (See 
> http://support2.overkalix.se/~sm2yer/shack/amp_mla2500/dentron_mla-2500b_cooling.pdf 
> <http://support2.overkalix.se/~sm2yer/shack/amp_mla2500/dentron_mla-2500b_cooling.pdf> 
>  )
>
> These modifications are to improve the high input SWR problem with 
> this amp. After very carefully checking all the joints and components 
> (except the RFC, more later) I powered the amp up and left it switched 
> on, idling for 20 or so minutes.
>
> I then systematically went through each band 10 - 160. The amp was 
> generating lots of RF and was stable on all bands, including 80m (if 
> you recall 80m was giving me lots of trouble).
>
> I then had a QSO on 80m with M0HEM, and received RST Reports as 
> expected. However, after around 5 or 6 overs, a crackling noise came 
> from the amp, the panel lamps dimmed, and the power falied to the amp.
>
> It turns out that the internal power fuse ( 10A Anti surge, or Slo 
> Blow in the US) had failed. I removed the covers and could not see any 
> obvious signs of arcing. The RFC that was replaced is RFC 4 on the ALC 
> board. In the manual I have (not the original) its down as a 15MH 
> Choke. Obviously not a 15 Mega Henry Choke.In other versions of the 
> manual, its down as 1.5mH  (Milli Henry) and others as 15uH (15 Micro 
> Henry).
>
> I suspect this has caused the problem, together with the very close 
> proximity of the moved components to the outer (earthed) case. I would 
> appreciate comments on the above, as I know think I'm getting 
> somewhere with the amp......as long as I havn't damaged the 8875's 
> !!!!!!
>
> Thanks all
>
> Adrian MW1LCR
>
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