[windy]

I have a spotmatic bought inJapan 1969.
need battery model and todays equivelant
thanks

[boriscleto]

There is no direct replacement unfortunately.

The Weincell MRB400 Zinc Air battery is the closest.

You can also get a CRIS H-B Mercury battery adapter that uses 377 silver oxide batteries. It has circuitry that reduces the voltage so the meter works properly. It costs more up front, but the batteries last longer...

https://www.amazon.com/Weincell-MRB400-Z400PX-EPX400-Battery/dp/B005AWSJLK

H-B Mercury Battery Adapter ? CRISCAM Webstore

[stevebrot]

There is no direct replacement unfortunately.

There is no direct replacement from a voltage perspective, but the camera's circuitry is fairly insensitive* to the voltage difference between the original mercury cell and currently available silver cells. The readily available 387S (or equivalents such as S400PX) is generally considered to be a drop-in replacement. It consists of a 384 silver cell pressed into a plastic grommet. The resulting cell fits into the Spotmatic battery compartment with no additional modifications.

I use the 387S and my Spotmatic meters (2) are linear through the specified sensitivity range and agree well with my other cameras and hand-held meters. That has been my experience, though YMMV.

It is worth noting that the H-B Adapter is a nice unit and has the advantage of being a replacement battery chamber cover as well as a voltage step-down adapter. The covers on most Spotmatics are in poor condition and replacements are hard to find. CRIS is not the only vendor for the H-B, so it may be worth shopping around, particularly if one is outside the US.

Wein or hearing aid cells (both zinc-air) are a poor solution since life is limited once activated.


Steve

* There are several threads both on this site and other places on the Web were the Spotmatic meter circuit is discussed along with appropriate diagrams. The circuit is an "unbalanced" variant of a Wheatstone bridge and generally needs no adjustment with 1.6V cells. If needed and with proper instrumentation (3μA tester), it is possible to tune the circuit to modern battery voltage using the general instructions in the Spotmatic service manual. http://www.pentax-manuals.com/manuals/service/servicemanuals.htm

[baldeagle21b]

There is no direct replacement from a voltage perspective, but the camera's circuitry is fairly insensitive* to the voltage difference between the original mercury cell and currently available silver cells. The readily available 387S (or equivalents such as S400PX) is generally considered to be a drop-in replacement. It consists of a 384 silver cell pressed into a plastic grommet. The resulting cell fits into the Spotmatic battery compartment with no additional modifications.

I use the 387S and my Spotmatic meters (2) are linear through the specified sensitivity range and agree well with my other cameras and hand-held meters. That has been my experience, though YMMV.

It is worth noting that the H-B Adapter is a nice unit and has the advantage of being a replacement battery chamber cover as well as a voltage step-down adapter. The covers on most Spotmatics are in poor condition and replacements are hard to find. CRIS is not the only vendor for the H-B, so it may be worth shopping around, particularly if one is outside the US.

Wein or hearing aid cells (both zinc-air) are a poor solution since life is limited once activated.


Steve

* There are several threads both on this site and other places on the Web were the Spotmatic meter circuit is discussed along with appropriate diagrams. The circuit is an "unbalanced" variant of a Wheatstone bridge and generally needs no adjustment with 1.6V cells. If needed and with proper instrumentation (3μA tester), it is possible to tune the circuit to modern battery voltage using the general instructions in the Spotmatic service manual. Pentax Manuals

Second the 387S battery.. It works fine and it doesn't need to be any more complicated than that. If you
have a Spotmatic F you can save battery power by loosening the mounted lens slightly so that the battery metering
switch opens up and disconnects the metering circuit from the battery.

[Bengan]

Since I couldn't get hold of the 387S in Sweden, I used a 384 directly. It's a tiny bit trickier to insert, but it works fine as long as you take care of polarity (+ in to the camera)

[windy]

much appreciated.
Ian