[ARC5] LM adventures

[Bill Cromwell]

Hi,

So I have an LM-13 and a BC-221. Both have homebrew power supplies
brewed by somebody else. I don't know how they worked at all and never
mind about how many years they worked. Both frequency meters stopped
working - in the same week! When I opened them up to examine the power
supplies - well it was revolting. The LM had the small power transformer
bolted in place. The recifiers and filter caps and the series resistor
were dangling with gobs of dried up tape here and there. One rectifier
was a selenium rectifier and the other was an early model silicon
rectifier in a full wave doubler. I think the filter caps were made in
1066 when William the Conqueror invaded England. I replaced everything
but the small power transformer with all new parts and mounted them all
on terminal strips securely bolted in place. Strangely enough that
supply was still working okay and the LM is still not working. I think
the VFO tube is kaput as there is no VFO signal but there is an audio
amp loafing happily. Back to that one later.

The BC-221 was worse. There is a power transformer in there capable of
running a nice little tube transmitter (6146 with a couple of driving
tubes)! There is also a filter choke. The small choke is the only part
that was fastened down! Some parts were actually mounted on two terminal
strips that were in turn mounted on an a piece of small angle iron. That
entire subassembly was roaming freely within the box. The long leads on
the series connected filter caps (two sections - four caps) were long
and bare and wobbly. The big iron was also floating around freely in
there. The strain relief on the power cord was mounted on the wrong side
of the bulkehead...outside the box! Maybe the original builder was
worried about that loose transformer pulling the entire power cord
inside the box <evil grin>. I removed the power supply intact and laid
it out carefully to sort it out. It has a high voltage, center tapped
transformer and is wired as full wave, center tapped. The filter is
capacitor input followed by the choke and then a second cap section. It
works just fine as is. On my bench the parts were not wandering around
shoring against the case while I had it laid out. The two screws, the
nut and the washer I found laying loose in the box were also not
visiting all those bare wires! The power switches in the meter do not
work! When this one is plugged in - it's on. I'll be fixing that. Going
to cleanup and rebuild the supply with better insulation and better
physical plant security aka nuts and bolts to hold things in place and
properly clothed with shrink tubing. This is a busy week but I'm hoping
to have the BC-221 back in operation before the weekend

Both power supplies are delivering ~400 volts DC. Thankfully the jumpers
are correctly set for that voltage. 

I was pleasantly surprised to find a spare Heterodyne crystal in the
BC-221 spares box along with a spare for one of the tubes. Whether or
not they are good remains to be determined. More later.

73,

Bill  KU8H