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07-09-2009, 05:20 PM   #1
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Spotmatic F battery question

Various sources seem to contradict one another on this. Can you use a 1.5v 625 battery for the Spotmatic F, or do you need a 1.35v Wein cell?

07-09-2009, 05:36 PM   #2
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QuoteOriginally posted by mabelsound Quote
Various sources seem to contradict one another on this. Can you use a 1.5v 625 battery for the Spotmatic F, or do you need a 1.35v Wein cell?
Yes, there is contradiction. Folks will swear that there is a dual circuit and therefore the 625 will work fine. They may be right.

Personally, I opt for the solution that costs a little more up front, but which uses inexpensive 3.5v cells and therefore over time more than pays for itself - with the added benefit that you KNOW the voltage is correct.

Interslice "Tri-Dot" Mercury Battery Adapter Guaranteed - eBay (item 120445589646 end time Aug-06-09 19:15:39 PDT)

<disclaimer>I am not affiliated with the seller. I am just a satisfied customer</disclaimer>

woof!
07-09-2009, 07:06 PM   #3
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Availability of batteries for the Spotmatic is better than other cameras of the era because the Asahi engineers built in a bridge circuit in the metering which makes it battery voltage independent. This means you can use the original 1.35 mercury battery, or a 1.5V silver-oxide replacement without problems.
07-09-2009, 07:47 PM   #4
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I put a 1.5 in my Spot F and it seems to work right. Should know tomorow, when I get the Pics back from the lab.

Steve N

07-09-2009, 07:58 PM   #5
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I use the Wein Cells in my Spot F. They have the correct voltage. I have used hearing aid batteries and an o-ring around it. I have never gotten around to ordering an adapter but will likely do that eventually.
07-09-2009, 08:06 PM   #6
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I use regular 625 1.5 volt batteries in my Spotmatic F. Gives me the same readings as my recently calibrated Gossen Luna-Pro meter.
07-09-2009, 08:11 PM   #7
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QuoteOriginally posted by raymeedc Quote
I use regular 625 1.5 volt batteries in my Spotmatic F. Gives me the same readings as my recently calibrated Gossen Luna-Pro meter.
Do you know why the mercury battery was originally used in these circuits?

Edit: I'll give you a hint. It is a similar reason that Lithium chemistry is currently used.

Last edited by Blue; 07-09-2009 at 08:17 PM.
07-09-2009, 11:20 PM   #8
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Mercury was used for 2 reasons:
- Flat discharge
- Loooooong life

Current 1.5v batteries do the job well and last for 1 year or so I have tried them in my Spotmatic, and the Spomatic F of my dad-in-law


Last edited by titrisol; 07-10-2009 at 07:11 AM.
07-10-2009, 05:40 AM   #9
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Good, I will try plain old 625's then. I have read online, variously, that the F is the only Spottie that has the bridge circuit, and elsewhere that it is the only one that DOESN'T have the bridge circuit.
07-10-2009, 08:08 AM   #10
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QuoteOriginally posted by mabelsound Quote
Good, I will try plain old 625's then. I have read online, variously, that the F is the only Spottie that has the bridge circuit, and elsewhere that it is the only one that DOESN'T have the bridge circuit.
There is a document with the circuit schematics for the F and others. There was a document for the Spot F meter circuit and others on the Pentax-manuals.com site but it doesn't seem to be there anymore.
07-10-2009, 08:26 AM   #11
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check in the Spotmatic group in yahoo, the docs used to be there
07-10-2009, 08:31 AM   #12
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QuoteOriginally posted by titrisol Quote
check in the Spotmatic group in yahoo, the docs used to be there
I have the pdf downloaded. I was going to link it. There were some typed notes about the bridged circuit being o.k. to different batter voltages. However, I'm cautious about the notes in the document.

I'd like to here Eric Hendrickson make a statement about the Spot F meter.
07-10-2009, 10:18 AM   #13
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QuoteOriginally posted by mabelsound Quote
Good, I will try plain old 625's then. I have read online, variously, that the F is the only Spottie that has the bridge circuit, and elsewhere that it is the only one that DOESN'T have the bridge circuit.
All Spotmatics had the bridge circuit, the difference being that the Spotmatics prior to the F took a smaller battery. Use a 387S (sometimes referenced as an S400PX) watch battery..... perfect fit for the earlier Spotmatics.
07-11-2009, 02:17 AM   #14
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I run Energizer 625's in both my Spotmatic F's and the metering is as accurate as it should be. I have a Pop Photo magazine review and the original manual, both of which back up the usage of the 625 cells, which have ALWAYS been a 1.5V battery, even when they were mercury based.
07-11-2009, 03:22 AM   #15
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PX625 mercury cells were rated at 1.35V. Modern replacements are rated at 1.5V but will work fine in the Spotmatic F.
The silver-oxide cell is harder to find and more expensive than the alkaline, but has more stable output and lasts longer.

Chris

Last edited by ChrisPlatt; 07-11-2009 at 12:19 PM.
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