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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