[Shuggzi]

I have just received what I thought was the correct replacement battery for my Spotmatic SPII, its from Wein and its model is MRB625 which replaces the PX625 and PX13.
It seems to be much larger than the original, its also larger than my K1000 battery as well. Have I ordered the wrong type or am I gonna have to run both my Spotm atic and K1000 with a battery for the light meter?

[victormeldrew]

The MRB400 is the correct Wein cell for the spotmatic...

[stevebrot]

Welcome to the Pentax Forums!

I'm sorry the Wein was wrong. The Spotmatic originally used a PX400, not the also-common PX625. The Wein replacement would be MRB400.

That being said, I strongly suggest that while Wein cells work well, they have a limited lifetime once activated and are generally not required as a replacement on Spotmatic cameras. The Spotmatic meter's "bridge" circuit is not voltage sensitive and works well with available silver-cell replacements. The Energizer 387S is the battery I use.* If strict 1.35V volt compatibility is desired, the H-B adapter (spacer with built-in step-down diode) is another good option. A happy side-benefit of the H-B is that it replaces the often bunged up battery compartment cover.

Your K1000 was designed to use readily available silver or alkaline batteries. I strongly recommend the SR44 (S76, 357) silver cell over alkalines.


Steve

* The 387S is actually a 394 with a nylon collar. When the battery dies, just buy a 394 and swap the collar from the old onto the new.

[edom31]

The Wein replacement would be MRB400

Side note - this camera SPII is one of a few that the battery is inserted positive side up... If you see that your light meter goes to the (-) side when it should mark an overexposure, then you have to flip your battery... This is the voice of experience speaking.

[victormeldrew]

The Spotmatic meter's "bridge" circuit is not voltage sensitive

This is a very commonly quoted misconception. While the circuit is basically a wheatstone bridge, it is in fact biased with a 3uA quiescent current, which is why the 'off' position is off-centre. While at high light levels the difference is small and not really noticeable, at low light levels the voltage difference will move the centre position significantly enough to give a noticeable exposure error.


Meter Modifications For Spotmatic Series Cameras - Pick My Camera

[stevebrot]

This is a very commonly quoted misconception. While the circuit is basically a wheatstone bridge, it is in fact biased with a 3uA quiescent current, which is why the 'off' position is off-centre. While at high light levels the difference is small and not really noticeable, at low light levels the voltage difference will move the centre position significantly enough to give a noticeable exposure error.


Meter Modifications For Spotmatic Series Cameras - Pick My Camera

This is true and obvious from the circuit diagram. I chose to use more general language in the interest of not muddying the waters regarding practical considerations for battery choice. I say "practical considerations" because light levels low enough to cause this problem are right at the lower edge of coupling limits (essentially low limit for meter sensitivity) for the camera with f/1.4 lens. As the linked article states, the error is on the order of 1/4-1/3 stops.* Most repair techs can tweak/modify the meter to work with modern batteries, but many will ask why bother. That was the conclusion of the article's author and my conclusion as well.


Steve

(...in the interest of full disclosure, Eric calibrated my SPII to use silver cells. The meter on it and my other (non-adjusted) Spotmatic agree and also agree with my Gossen Luna Lux and that is good enough for me...)

* That would be attained by carefully nudging the aperture ring between the f/1.4 and f/2 while conveniently forgetting that the slow speed precision of the shutter below 1/8s is dismal.

[twilhelm]

For cheap, off the shelf batteries, I use size 10 heating aid batteries with an o-ring. They are 1.4 volts and I haven’t noticed the meter being off (though I realize in low light it can be). They only last 1-3 months, but $8 for a 10 pack is cheap.

[stevebrot]

The Energizer 387S is the battery I use.* If strict 1.35V volt compatibility is desired, the H-B adapter (spacer with built-in step-down diode) is another good option. A happy side-benefit of the H-B is that it replaces the often bunged up battery compartment cover.

It occurred to me that it might be useful to provide additional information about these two options, specifically, approximate cost and places to purchase.

• Eveready 387S (the "S" is for Spotmatic) batteries are available on Amazon for about $5 USD per battery or about $15 for a lot of five. The 387S should last 1-2 years in moderate to regular use. These clever adapted cells are also available through other outlets. Use your favorite search engine with the term "387S battery".
• The H-B adapter (voltage step-down diode built into a Spotmatic battery chamber cover) is sold in the U.S. by CRIS Camera Repair in Arizona for about $36 USD. One may also buy directly from the maker, Kanto Camera in Japan, for somewhat less money than from CRIS (at today's exchange rate, $24.99 USD). They also make the MR-9 adapter that uses SR44 cells as a replacement for PX625 mercury cells. I bought my MR-9 from Kanto and could not be happier with its performance on the cameras it fits.

  Kanto Camera: Battery Adapter

Steve

[Shuggzi]

Thanks all for your input, I ordered the correct battery yesterday afternoon and received it today, that was fast postage for the UK, got it from a company called smallbattery.company.org.uk £5.95 with free postage


Shuggzi

[stevebrot]

Thanks all for your input, I ordered the correct battery yesterday afternoon and received it today, that was fast postage for the UK, got it from a company called smallbattery.company.org.uk £5.95 with free postage


Shuggzi

Cool!

Should you find the Wein cell life span unsatisfactory, Small Battery Company also sells a 387S equivalent and the H-B adapter. Enjoy your Spotmatic II.

Small Battery Company | PX400 Page


Steve

[jjbuzard]

In My Spotmatic and My clip on Light Meter for my SV I use a Energizer 357 Silver Oxide Battery and an 7/16' x 5/16" x 1/16" o-ring fits perfect. You can buy these batteries ANYWHERE, long life too!