Marantz 10B opto couplers
- Thread starter stanko
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Stan,
I just restored a 10B and, fortunately, the opto couplers were all good. I thought the mono switch might be bad, so I did some on line digging and didn't find anything obvious. The couplers are basically a cadmium sulfide photo resistance cell (or two, for the stereo switch) embedded with a neon bulb inside a light-tight closure. The closest thing I found was this Fender-type coupler used for tremelo in guitar amps at TubeDepot:
https://tubedepot.com/products/opto-coupler-ldr-for-fender-amps
And I found an old Audio Asylum thread on same that provided info but not much in the way of current solutions:
https://www.audioasylum.com/cgi/t.mpl?f=tuner&m=8300
Apparently, someone used to make custom-made replacements, but I could find no evidence that anyone still does.
I expect that with experimentation you could figure out what the resistance of the photo cells would need to be. I also expect the 10B couplers just use NE-2 bulbs, like the start up bulbs they installed under the chassis.
I actually bought a couple of the Fender replacement devices, but didn't do any further testing on them to this point.
Dave
I just restored a 10B and, fortunately, the opto couplers were all good. I thought the mono switch might be bad, so I did some on line digging and didn't find anything obvious. The couplers are basically a cadmium sulfide photo resistance cell (or two, for the stereo switch) embedded with a neon bulb inside a light-tight closure. The closest thing I found was this Fender-type coupler used for tremelo in guitar amps at TubeDepot:
https://tubedepot.com/products/opto-coupler-ldr-for-fender-amps
And I found an old Audio Asylum thread on same that provided info but not much in the way of current solutions:
https://www.audioasylum.com/cgi/t.mpl?f=tuner&m=8300
Apparently, someone used to make custom-made replacements, but I could find no evidence that anyone still does.
I expect that with experimentation you could figure out what the resistance of the photo cells would need to be. I also expect the 10B couplers just use NE-2 bulbs, like the start up bulbs they installed under the chassis.
I actually bought a couple of the Fender replacement devices, but didn't do any further testing on them to this point.
Dave
Image below shows what’s contained in the dual version of 10B opto coupler module. Potting compound was poured on top of the foam disc with the leads to seal the unit.
This particular one had two failure modes: 1. Weak NE2 that wouldn’t reliably “fire”, and 2. CdS cell leads that had become unsoldered from the CdS substrate. Both issues contributed to intermittent operation. As I observed elsewhere, these opto couplers strike me as not up to the Marantz brand image of the time. They should have used hermetic CdS cells and long life neon lamps.
This particular one had two failure modes: 1. Weak NE2 that wouldn’t reliably “fire”, and 2. CdS cell leads that had become unsoldered from the CdS substrate. Both issues contributed to intermittent operation. As I observed elsewhere, these opto couplers strike me as not up to the Marantz brand image of the time. They should have used hermetic CdS cells and long life neon lamps.
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I’m aware of no published spec for either the optocouplers assys or the CdS cells. My notes indicate a dark resistance of >20MΩ, ~ 60 Ω in bright light and ~ 200 Ω in the light of a new NE2 close coupled to the cell and driven with DC (only 1 of the 2 wire electrodes illuminated). I don’t think the absolute value of the resistance is too critical but if you have a properly operating optocoupler, by all means measure it in its two states.
Thanks for those numbers. They are a start. I'm gonna try and come up with something measuring what I have., if I do, I will post it. The couplers I bought many years ago do operate correctly, so I think it's just a matter of getting the right cells.
DavidAlm
Member
Hello stanko. The replacements that you have....were they purchased off of Ebay and manufactured by a gentlemen named Mirko? Is the opto-coupler that you are now having issues with one of his?
I purchased a set from him back in 2013. Since then I have purchased another 10B that needs couplers. I emailed Mirko this past November and never received a response. So I too am thinking of fabricating my own.
Have you made in progress in trying to determine the correct photocells?
Thanks,
David
Hi David; I don' remember the name. I just put one in of my units and it works fine. I have not done anything but search online for subs. There are a lot of opto couplers out there, whether they work is another matter. Some guitar amps use them, don't remember which.
Don Lubin
Active Member
I don't know the specific requirements for the 10B optocoupler but it sounds like it needs an element where the resistance drops when the lamp goes on. Has anyone looked at low power enhancement mode solid state relays as a replacement? They perform the same function so it would be a matter of looking for the right terminal characteristics to match the 10B circuit.
![IMG_3091[1].JPG](/forums/data/attachments/2092/2092677-a87b1f425401547a8bd96ca226f059aa.jpg?hash=qHsfQlQBVH "IMG_3091[1].JPG")
When I mentioned “long life” neon lamps, it was a very general wish without specific recommendation.
Looking over the specs of an NE2 in an older Newark catalog, “life” is rated at 25,000 hrs. This would be 17+ yrs at 4hrs use/day, probably well beyond design life of the 10B. However, this rating is presumably for AC apps where both electrodes are lit. With DC applied as would be the case with the 10B opto isolators, I’m not confident that 25K hrs applies. Personal experience with NE2s used as pilot lights would suggest that 25K hrs is very optimistic. Also, the 10B app is fairly critical as to lamp performance. Consider too that at some point while the 10B was “current”, Marantz issued a service bulletin regarding the opto isolators and how to test them in-circuit for proper operation. Obviously, Marantz knew they had a potential problem with opto-isolator life.
I don’t believe Marantz really understood the nature of neon lamp life characteristics when they designed their opto-isolators and used off-the-shelf NE2s instead of something custom designed for the purpose. An additional confounding factor is that apparently some lamps of the era used a mildly radioactive element to promote proper firing under total dark conditions. This element has a half-life of ~10yrs. And they used low cost plastic CdS cells without appropriate lead strain relief. All of this adds up to a great potential for long term opto-isolator issues.
Bottom line here is that I know of no readily available “long-life” NE2 replacements. Your old stock NE2s should probably perform about as good as anything else you could find today short of LEDs which would require very major circuit redesign to use. However, I would “select” them for reliable operation under conditions imposed by the 10B...probably something Marantz didn’t do.
DavidAlm
Member
Steve O, I have a Service Bulletin that is titled "Marantz Model 10B Check-Out." It is number 69-11/10B-1 and is dated 9-19-69. Is that the one that you are referencing?
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Mine still work so hopefully I never need to try this but I read this on the Klipsch forum. No idea if it's actually this simple or even works:
Marantz 10B Photocells: This is actually a minor problem: They leak usually, because they are not properly closed anymore. They let light in then (sorry for my bad English). All that needs to be done is to carefully open them and laquer them newly. That's all, and then they work fine again. No need to get new ones."
Marantz 10B Photocells: This is actually a minor problem: They leak usually, because they are not properly closed anymore. They let light in then (sorry for my bad English). All that needs to be done is to carefully open them and laquer them newly. That's all, and then they work fine again. No need to get new ones."
Yes, that’s the one. From the date I assume it comes from the Superscope era. The instruction to heat the optocouplers with 170°F air makes me cringe a little considering the jam packed 10B chassis.
DavidAlm
Member
Shawnnnn, do you have a link to that post from the Klipsch forum?
