Minolta SRT CdS cell - looking for NEW

GBS

GBS

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Hi all!

Does anyone know where to find NEW CdS cells for a Minolta SRT? I have about 3 cameras that are declining in sensitivity and linearity, so the meters can no longer be calibrated across the full range of EVs. I have verified with 2 techs and other electronics sources that old CdS cells do, in fact, go bad over time. Sadly. I'd rather not cannibalize another camera, even a parts camera, as those cells will eventually go bad too.

Here's what I know:
- The ones in the Minolta are TO-5 form factor (but anything about ~8mm or smaller will also fit)
- Advanced Photonix makes new cells, but I'm still testing mine (after APx sent my good samples back with no recommendations). Furthermore, their data sheets don't correlate to usable EV easily.
- APx told me CdS cells have a low profit margin and are not RoSH compliant, so they're not widely-manufactured. (Apparently APx are the only game in town (or the U.S. for that matter).

I came across two posts that could be used to make some progress, but I am not experienced enough in electronics to re-engineer my circuits, though I would be eager to help traverse that curve if the CdS cells could be replaced with newer, RoSH compliant Photo Transistors.

This person built a new meter using the SRT as a guide:
www.filmkorn.org

Building a new light meter for the Bolex D8L

The components of cameras age and lead to a loss of functionality, but some cameras, namely those from Bolex, Leitz or Beaulieu, to name just a few, seem to be built mechanically for eternity and c…
www.filmkorn.org www.filmkorn.org

This is a CdS cell meter repair guide:

Any leads would be appreciated.
 
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xkaes

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Have you tried major repair shops to see if they have a source?
 

Paul Howell

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Got this from ChatbotGPT

There are several companies that manufacture replacement CdS (Cadmium sulfide) cells for vintage 35mm cameras, although availability may vary depending on the specific camera model.

Some popular manufacturers of replacement CdS cells include:

  1. Mr. Butkus (http://www.butkus.org/): Mr. Butkus offers a range of replacement CdS cells for various vintage camera models, as well as repair manuals and other camera accessories.
  2. Focal Point (https://www.focalpointlens.com/): Focal Point specializes in replacement CdS cells for vintage cameras, including popular models such as the Canon AE-1 and Nikon FM.
  3. Micro Precision Products (http://micro-tools.com/): Micro Precision Products offers replacement CdS cells for a wide variety of vintage camera models, as well as other camera parts and accessories.
It's important to note that replacing a CdS cell in a vintage camera requires a certain level of technical knowledge and skill, so it's recommended to consult with a professional camera technician or repair shop before attempting to replace the cell yourself.
 
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GBS

GBS

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Yeah, no. None of those leads seem to be accurate.
 

BrianShaw

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Give the bot some time to mature. Look at how Wikipedia evolved from a morass of stuff to become as citable as a juried academic journal!
 

4season

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Without knowing exact specifications of the original part, some guesswork is needed. By measuring maximum and minimum resistance of original cells, you can perhaps get a ballpark idea of what's needed. As for where in the visible light spectrum peak sensitivity should be, I don't know, but 550 nm is pretty much in the middle of the visible light spectrum. Digikey makes it easy to sift through Advanced Photonix offerings, and with even partial information, you can probably narrow the selection down to just 1-2 items.

https://www.digikey.com/en/products...bRACYAGAThAF0BfAmcqUZSAFwCcBXfIqRABWEAVqMGDIA
 
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GBS

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Thank you! I actually got a couple from APx that were the closest match, but not drop in replacements. I may need to rebuild the circuit with a different variable resistor, but I’d need help.
 

ppg677

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Did you ever find any suitable CDS cells? I have a couple SRTs that simple don't have sensitive enough cells.
 
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GBS

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ppg677 said:
Did you ever find any suitable CDS cells? I have a couple SRTs that simple don't have sensitive enough cells.
Click to expand...

Hi,

I ended up spending 2 years trying figure something out and arrived at what may be the closest we'll get. I'm making new cells. An Initial test in my SRT shows accuracy from 5-15EV. This is inside the original 3-17EV, but I have to look at it as a win. The only time you'll be off is if you meter in the sand or snow and manually compensate. Those scenes are about 17, but since the meter caps out at 15, you'd underexpose if you meter the snow and compensate. But under normal conditions, it's pretty rare to see over 15 in the real world. I generally set my meter for sunny scenes to the blue sky anyway (or my open palm filling the frame in the same lighting conditions, then open +1 from there), so if you meter for a blue sky that would make snow/sand expose correctly.

The cells will be about $22 for the pair, shipped in the US, but I'll be happy to send you a pair for cost, which is $15 shipped next time I put a few together. I'll attach a rough photo, but ignore the extra resistor, though you do have to do a slight rewiring--and you can't replace only one, unfortunately. I don't have a photo of the final build as I have PTSD thinking about taking the lid off again now that it's working. But I'll get to that and create a guide - eventually.

Let me sign off by asking: are you sure the cells and the prism wedges they're attached to are clear and secure? Often, the glue yellows and they come loose. But you may already know that.
 

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Richard Jepsen

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I have a SRT bought new in 1969 or 70. The metering just failed and I’m unsure if its a battery or cell issue. This is a nostalgic camera but I will use a hand meter in the future.
 

dynachrome

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I would just send an SRT to John Titterington. He has done excellent work on my SRTs and other Minolta cameras.
 

ppg677

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How are you making new cells? I assume you sourced some CdS cells somewhere? What is the resistance range of the cells you are using?

I've got a couple SRTs. One is not very sensitive.

I've got an SRT202 where the resistance of the CDS cells are just way too low (causing the needle to max out). Like 200 ohms rather than the more typical 5000+ ohms. I was thinking about swapping in cells from a donor camera that has a bad shutter.

Any tips for removing the glue of the existing cells? I have some B7000 adhesive (used to attach phone screens) that might work to reglue cells.

At would be easier to just swap the entire prism from the donor camera, but the donor camera (SRT 101) doesn't have the extra little prism piece to project the aperture onto the viewfinder...though maybe that is just glued on and would be easy to unglue/re-glue that little piece compared to CdS cells.
 
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reddesert

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CdS photoresistors themselves are a common item. They may not have many US manufacturers, but you can buy them from Tayda Electronics for US $0.29 a piece: https://www.taydaelectronics.com/resistors/photoresistors.html The problem is that for light meter use, you either need to match the resistance of the original cell at a couple of light levels, or have some way of trimming / adjusting the circuit to match.
 
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