----- Original Message -----
From: "Eric Goldstein" <egoldste@xxxxxxxxx>
Sent: Monday, October 16, 2006 8:52 PM
Subject: [rollei_list] Re: Krimar speed
I will not quote from a web site without express permission.
referenced sites show/state that alkaline cells show an
in voltage over the life of the cell from about 1.55 volts
to about .9
volts. The voltage drop begins early in the life of the
the meter circuit is regulated, this will result in a
drift for a given quantity of light. Mercury and Silver
are virtually consistant and flat in their discharge voltage
life of the cell. If Krikor's recalibration were done
quickly with an
absolutely fresh alkaline cell, then it should be ok for
cells which will give consistent readings.
I have been suffering from a pinched nerve in my back
again and have been away from the computer.
Eric is right about Mercury cells and Alkaline cells.
Mercury cells have been used for applications requiring very
stable, constant, voltage for perhaps 70 or more years. They
were common as a supply of grid bias in portable electronic
instruments until the advent of transistors. In these
applications they were often soldered into circuits as
Alkaline batteries of all types have a constant
diminuition of voltage even when not loaded much and also
have relatively short lives. The meters using Mercury cells
did so to avoing having to use some method of voltage
Generally, Mercury cells and batteries (technically a
battery is more than a single cell) have the property of
maintaining their voltage until very nearly the end of life
at which point the voltage drops very rapidly to virtually
nothing. This was a great problem with the early radio
microphones used in television and motion pictures because
one never knew where the battery was in terms of life so it
was common for mics to fail suddenly on air. The answer was
simply to put new cells in right before air time and to have
lots of spares (both mics and batteries).
Since these microphones drew considerable power from the
battery the life was not as long as in low drain
applications like bias cells and light meters.
AFAIK, no other battery type has the combination of long
shelf life and constant voltage of the Mercury cell but
Silver cells come close. The use of other batteries with a
simple regulating diode and resistor will result in even
more stable voltage than the Mercury cell and is probably
the best solution. The voltage drop across the diode is
extremely constant. To some degree, this system has the same
trouble as the Mercury cell, namely, when the battery
voltage drops too low the regulator no longer works and out
put can become very low or unstable.
The main difficulty of using a regulator diode is finding
a place for it. Some adaptors have been made to fit existing
Silver Oxide batteries, which are smaller than the Mercury
cells, but the diode and resistor can be installed inside a
lightmeter or camera if the insides are at all accessible.
Los Angeles, CA, USA
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