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How well does a MR9 battery adapter work?

Very well, they reduce the voltage of a 635 silver oxide batteries from 1.55 volts to the correct 1.35 volts, and give correct exposure.
 
They are bit expensive at first but it works really well.
 
Work great. The best part it that the batteries inserted can be found in every drug store.
 
They work great. I have them in in a Nikon F FTn meter head, and used them when I was shooting with an Olympus OM-1. Better than Wein cells and the 1.5v Silver-oxide batteries can be found everywhere.

They are a bit expensive, but I usually keep the adapter if I sell the camera.
 
I use them in my Yashicamat 124G and in my Minoltas. They work very well. Both came with cameras I bought on e-bay so I have no idea of their actual cost.

I am not sure about the Yashica, but there are instructions online for fixing the Minolta on your own by inserting a small resistor to bring the voltage down. You will still need to find a rubber o-ring to put around the battery so it doesn't move around in the larger battery compartment.

Of course, in both those cameras, a handheld meter will completely negate the need for a battery at all, eliminating the additional expense.

I guess it all depends on the amount of time or money you have at your disposal.
 
What do you mean--you have 2 MR9s in the F meter head??
 
Had one in my CL while the meter still worked, now it lives in my Rollei 35S.
 

Any non-mercuric oxide battery (except the air cells) have continuously variable voltage output during their entire life, and any camera which does not rely upon a Wheatstone bridge circuit meter design will NOT tolerate the variable voltage, unless the output is regulated to 1.35v during the slope from 1.5v to 1.25v that the battery puts out. A resistor provides no voltage regulation! The MR9 output is apparently regulated to 1.35v at all times.
 
Rather than a resistor, it is a schottky diode that is used to regulate the voltage.
 
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I use two MR-9s: one in my Rollei 35 and in my Gossen Lunasix.

They are perfect!
 

Silver Oxide batteries maintain a much flatter voltage curve than alkaline batteries. A 1.55V Silver Oxide cell with a BAT41 Shottky diode to drop it by .2V will give you a pretty constant 1.35V as long as you stay below 200uA of current draw.
 
I've used it in my Canon FT and Zenit TTL with good results. I now have it (the same one) in my SRT101 testing out a recent CLA.
 
Thanks for catching this wiltw. Sorry about the misinformation over the resistor. I have done the upgrade so this was pure brain fart on my part.

BTW - I do agree it is worth doing on the Minolta. Having never done it to the Yashica Mat I don't know what is involved so have continued to use the MR9.

 
I have 3 MR9's, 2 in my Canon EF and one in my Canon F1n, and they all do what it says on the tin and run on without any problems on easily obtainable 635 silver oxide watch batteries. If you want to buy one, as far as far I know the only company in Britain that sells MR9's is The Small Battery Company in London http://www.smallbattery.company.org.uk/
 
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Quality product. My camera meters match my Gossen meters within 1/2 stop. Buy with confidence. Good investment that restores great old cameras to full operation.

John
 
My Canon F1n with the MR9 adaptor and a 386 silver oxide battery installed matches my four Canon New F1's that all have the correct PX28 battery in them when checked against each other with the same Canon FD 50mm f1.4 lens on each of them using a Kodak Grey Card and a 1° digital spotmeter within less than 1/5th of a stop which is negligible and it allows one to use many great old cameras to the best advantage without modification.
 
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