One for the electronics boffins

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I've acquired a faulty Crotech audio signal generator. The fault appears to lie in an opto device marked 'Moririca Photocell-Lamp MCL-703C' - the photocell part seems to be open circuit. RS and Maplin drew a blank. Moririca have a web site, but I can't locate it there as it's probably obsolete. Any suggestions?
--
* What do they call a coffee break at the Lipton Tea Company? *

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Dave Plowman wrote:

Similar topic was discussed on sci.electronics.repair a while back, IIRC there is a company called Vactec who still make these lamp/LDR type devices. They call them a Vactrol ... They are normally used as a voltage controlled resistor, so a non-original sub is bound to throw off the calibration :-(
Lee
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Lee Blaver wrote:

Mmm. Even an on spec one will still need recalibration.
Curious as to what its doing - controlling amplitude perhaps? Yerrrs. I built a fairtly good oscillator once and used something like that. Thermistor possibly.

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There are dozens of tweaks in it. Gawd knows what they do, but the one associated with the LDR is obvious.

I built a Maplin kit which uses a lamp on its own. They make a cheap thermistor.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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wrote:

Wien bridge oscillator - pretty common to have a thermistor in there, if it's a low-distortion sine generator. I believe the optical variant is less environmentally sensitive and less prone to going out of tweak with change of temperature.
It shouldn't even need much adjustment, just allowing to warm up and become stable.
(cont. old_moog_tuning_stories / "I was Rick Wakeman's curry roadie")
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Right - one more for the search engine.

The tweak for it is fairly obvious - luckily, as there are hundreds of them. It's quite a complicated beast and must have cost when new.
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*Sometimes I wake up grumpy; Other times I let him sleep.

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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On Tue, 26 Aug 2003 22:36:26 +0100, Dave Plowman

suitable bulb and an ORP12 photoresistor taped together? Wasn't this a system used in a number of old oscillator circuits to stabilise them?
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Peter Parry.
http://www.wpp.ltd.uk/
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It's quite a large device - about an inch long and 1/4 in diameter with the connections for the bulb and photo resistor at either end, so it would be easy enough to fabricate one if I had the spec. The bulb is fed with 12 volts - I haven't measured the current yet.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Dave Plowman wrote:

I think my glasses need cleaning, or filling, I read that first line as "I've acquired a faulty crutch".
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James...
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On Wed, 27 Aug 2003 01:11:00 +0100, Dave Plowman

As in "I've got a friend with a discharge..." etc. etc......
Not really wishing to mention the obvious but did you try contacting Crotech?
.andy
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On Wed, 27 Aug 2003 19:21:32 +0100, Dave Plowman

http://www.crotech.co.uk/ ???
.andy
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On Wed, 27 Aug 2003 22:05:24 +0100, Dave Plowman

Service isn't sexy though, is it? Looking at it, neither is Crotech's selling web site, mind you.....
Hopefully they can help - these are a useful thing to have....
.andy
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Found an e-mail from Moririca waiting for me when I got in this evening.
They can supply 10 as a minimum order for 650 yen. Must look up the exchange rate...
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*I like cats, too. Let's exchange recipes.

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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snipped-for-privacy@argonet.co.uk says...

About 3.50 - Bargain!! (Unless it's 650 yen each..)
Peter
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Sadly it appears to be the unit price. So probably about 40 quid including carriage. I've e-mailed Crotech about spares. ;-)
--
*Bills travel through the mail at twice the speed of cheques *

Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Dave Plowman wrote:

Have you tried http://www.mushroom.co.uk/ or similar, they're obsolete stock specialists according to an ad I spied at work today so might have a good idea where to look.
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James...
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E-mailed them - no reply. Got their phone number off the website - unobtainable. And don't you just love it when they don't give the full UK number? Try faxing them - it rings, but no reply. Try new directory enquiries - get some american bird who gets me Protech - same area code though. Try another directory company. No listing for Crotech. Try the new BT one. They have no number but give me an address which is different from the website one.
I've written to both the addresses. But I have a feeling my pal may have been right. So whether it's worth paying out 40 quid + to get it going properly, I'm not sure.
--
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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It is going to be something like a filament lamp and photoresistive cell arrangement. Can you consider knocking it apart and duplicating it? The critical spec will probably be the Volts/Amps of the lamp.
--
Tony Williams.

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I'm not sure what the original resistance of the device was but about 1-2 k is what works empirically feeding the next stage which I haven't attempted to measure the input resistance of.

This device is about 9mm in diameter - I'd guess simply a tube with the bulb at one end and the whatever at the other. It has a symbol for a bulb and a resistor to denote the ends, so I assumed it was an LDR. It's quite big enough to allow fabricating a replacement mechanically easy.

I'll do just that.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Dave Plowman wrote:

The ORP 12 photoresistors from memory, were tens of K in the dark, a few K in room lighting and a few hudred ohms in bright light.
Plenty of variation to ensure that you get a distortion-free output.
Its the amplityude that is teh problem as even slight variations in bulbs can give a siignificant variation in output.
You will have to re-calibrate the amplitude - but thats usually one adjustment somewhere, and can be done with a good DVM.

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