Would
the small "coin" cells be useful for bias battery replacement? I know
they are available in 1.5 and 3 volt types, the holders/sockets are not
much larger than the batteries, and have solder tabs. Both the cells
and the sockets are very inexpensive.
My
recollection is that the original battery was 4.5 volts, so you could
put three 1.5v in series or a 1.5 and a 3v in series to get exactly what
is needed. I think there are taller sockets that will hold a stack of
these cells - if you can find one that would hold three 1.5v cells it
would be perfect.
I
have also had success stacking several coin cells, placing stripped
hookup wire against each end, and putting heat-shring tubing over the
whole business to pull it all into contact. An example of this is right
here on my office desk - a small stack of coil cells powers the code
practice oscillator I mounted on a key base for people to play with. I
send a little Morse to them if they seem interested. Here's a photo
showing the heat-shrunk battery pack in the lower right corner:
http://www.wd8das.net/Office-Key-2.JPG
I
have more often used these coin cells to retrofit into a radio with a
dead memory backup battery. Often the original type is obsolete or hard
to get, so I usually select a more common type of the right voltage.
Size might not be exactly right and I can't mount the new one exactly
like the old one, so I end up connecting the socket to the board with
hookup wire, putting the battery and socket into a small ziplock bag to
insulate it (and maybe catch any future leakage), and tuck it wherever I
can find some space.
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Radio is your best entertainment value.
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Mein Ohr ganz nah am Weltempfänger...