This meter used the now unavailable mercury PX-14 2.7v battery. But it can be converted to use the common 1.55v silver oxide battery.
Why use the silver oxide battery instead of the 1.50v 625 alkaline battery? Or even the 1.4v 625 wein cells? Simple. The alkaline battery starts to drain as soon as you start using it which means your meter readings will be off, usually as much as 2-3 stops underexposure with new cells because you will have a combined voltage of 3.0v (more than the required 2.7v) and will only be accurate for a short time when combined voltage is 2.7v then will overexpose till the cells finally drain. The wein cells have a life span of around 1-2 months (the ranger 9's current rating is approx.50µA-1875µA which will drain these cells faster) whereas the silver oxide battery has a nearly identical voltage curve as the original mercury battery. The voltage stays constant throughout its life span.
Converting the Weston Ranger 9 to use 1.55v silver oxide batteries instead of the poor substitute alkalline 625's and 625 wein cells is a very easy task. If your meter has been calibrated for 3.0v in order to use alkaline cells, you will have to have it re-calibrated to original factory specs before converting it to use silver oxide batteries. Another option which I have not tried is to order 2 s625px silver cells from Photobattery.com. The difference in voltage between the alkaline and silver cells is 0.10v if using 2 cells and may or may not affect the actual meter readings.
You will need 2ea. BAT 43 or BAT 46 schottky diodes, a straight slot screwdriver, wire cutters, solder gun, solder, and electrical tape.
First you remove the large center screw on the dial. Remove the dial assembly and remove the 2 screws you just exposed. Carefully remove the front cover and set it aside. You will notice 2 wires coming from the battery compartment. One will be soldered to a ground lug and the other will go the the circuit board (usually a black wire). Un-solder the wire going to the circuit board (not the wire soldered to the lug) and strip off approx. 1/8th inch of the insulation and tin each end.
Referring to the below diagram, solder 2 schottky diodes together. Be sure to cut the wires to where you will have approx. 1/4th inch space between diodes. Now cut the end wires to approx. 1/4 inch and solder the anode end to the wire coming from the battery compartment and the cathode end to the wire going to the circuit board. A word of caution: Don't over heat the diodes while soldering or you will destroy them. Now carefully insulate the diodes and exposed wires with electrical tape and position them so as not to short out on any metal parts and replace the cover and dial. Be sure to position the dial so it aligns with the pin in the cover.
You now have 2 options for battery cells. You can either use the s76 or 357 with a spacer and spring or order the S625PX size silver oxide battery from Photobattery.com
If you use the s76 or 357 cells, you will need to make a spacer from
plastic per the below diagram.
You will also need a spring and insulating washer to prevent the spring from
making contact with the battery edge which is the +. A spring will also be
needed if you use the 625 size silver oxide batteries.
If you need to calibrate the meters battery check, remove the 2 small screws on the back of the meter. Referring to the below sheet, adjust R5 till the battery check indicates proper alignment with the red indicator mark on the meter dial.
Due to Weston using different variable resistors throughout the production of this meter, some battery check circuits will not be adjustable to the red indicator mark. If yours is this way, you will need to set a different mark, usually between 16 1/2-17.
Forward voltage is approx. 3.0v with the 2 schottky diodes installed and drops to 2.7-2.8v when a load (light measurement) is put on the meter. At low to medium light readings, measured voltage is approx. 2.6-2.8v and drops to 2.5v at heavy load. When I subject the meter to light too bright to measure, voltage drops to 2.4v.
I get identical readings with a Ranger 9 with the original mercury px14 2.7v battery installed in a non-modified meter.
Forward load voltage of 2.5-2.8v is correct for the this meter and will give accurate readings, therefore this modification is the best alternative since it gives identical readings to the original battery.
Calibrating your meter to use 2ea. 625 1.5v alkaline cells give approx. 3.3v and drops to 2.9-3.0v under load which is slightly too much voltage for accurate readings. Once you burn off approx. 0.3v, your meter will be accurate till voltage drops another 0.5v. The alkaline cell looses voltage as soon as you put a load on the meter and continues to drop. Alkaline has a very sharp voltage curve and only gives you accuracy through only about 10% of its life span...not very cost worthy..
Please note: The above tests were conducted over a 1.5 year period at ambient temps. of mid 30 degrees - over 100 degrees. Temps below freezing will cause the battery to lose voltage and would require keeping the meter warm. Therefore testing was not conducted below 30 degrees.
If your meter ever needs repair or adjustment, contact
George Milton
Quality Light-Metric
7095 Hollywood Blvd., Suite 550
Hollywood, CA. 90028
(323) 467-2265
Contact Quality Light Metric at QLM
A word of caution.. DON'T let any repair shop talk you into letting them calibrate your meter to take the 625 alkaline battery. As stated above, this battery is a poor substitute and will give incorrect readings.
If you have any questions or comments, contact me at fotografs@swbell.net