AUTOCORD : the Minolta's TLR
by Fred
Description
The CDS lightmeter cell requires an Eveready EIN or Mallory RM-1R mercury battery developing a tension of 1,35 V.
Advantage : the tension is stable throughout the life of the battery. The death is rough.
Inconvenience : the mercury is toxic.
This type of battery is no longer manufactured since the 90s.
Solutions exist.
Alternatives
1) The zinc-air batteries : A 675 .
Zinc - air batteries are designed for hearing aids , they give a voltage of 1.4 V.
They need air to work .
Advantage : attractive price.
Disadvantage : they can not be inserted in a sealed housing ;
short life span : 2-3 months as soon as the membrane is removed , the battery wears out even if you do not use the device .
The A 675 is a little short (5,4 mm) and a little small (11,6 mm), it needs to think about a D system to use it.
2) The zinc-air batteries : MRB 625.
Same principle but the voltage is 1.35 V.
Disadvantage : high price, allow 30 min after activation stabilize the battery voltage.
3) Alkaline batteries : PX 625A (or LR9) and A1PX (or LR50).
Alkaline batteries have a voltage of 1.5 V.
It's a bit much, the light measurement is slightly overestimated .
Over time, the voltage decreases slowly. So the correction to be made to the camera settings will no longer be valid.
Then the tension further decreases and the correction must be expressed in the other sense pending battery replacement.
The LR50 has the same dimensions as the original Mallory RM-1R.
4) MR-9 or MR-50 adapter.
These are false hollow piles provided with a strenght lowering the actuel batteries voltage to 1.35 V.
They are made to be used with SR44 (or 357 - 303 - SR1154 - SR76E) 1.55 V silver oxide battery.
Two models are on the market :
a) MR-9 (short) : replaces the PX 625 battery ;
b) MR-50 (long) : replaces the alkaline LR50 and the mercury oxide RM-1R.
Disadvantage : high or exorbitant prices.
Advantage : a single adapter for all devices that require mercury battery ( unless you use multiple devices at the same time).
The MR-50 has the same dimensions as the original Mallory RM-1R.
The MR-9 is less high and requires the addition of a small ball of cotton wool or paper towel to fill the free space.
The silver oxide batteries are affordable, the discharge curve is gentler than alkaline.
Life time
Oddly , sometimes you can find an old PX625 mercury battery stock from the 1990's .
But what could be the life of the mercury cell ?
I don't know.
However, I'm using one for my Yashica YEM35 Super light cell and I do not know when it was made .
Remember to drop your used batteries to collection centers and / or sorting to recycling.
If you think your CDS lightmeter doesn't want to operate, contact me.
Use the "Contacte me " page.