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?
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 :-(
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.
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.
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")
stopped producing the MCL series a year ago. It might be worth an email to snipped-for-privacy@moririca.com to see who their UK distributors are and checking for one kicking around?
I e-mailed them last night, and had a reply by this morning - rather a change from most UK companies who ignore e-mail. I've copied the relevant bit below:-
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Unfortunately, MCL-703C became the discontinue line several years ago because one of the material parts could not be supplied to us. Checking the stock in our factory, there are only 18pcs on hand. We can supply them with the sample price if you would like to.
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I'm not quite sure if they want me to buy the lot, or are offering just one. But I've e-mailed them asking for a price. I expect the reply will be tomorrow due to the time difference.
Full marks to Moririca for bothering to answer on such a trivial thing.
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.
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.
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