One for the electronics boffins

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

suitable bulb and an ORP12 photoresistor taped together? Wasn't this a system used in a number of old oscillator circuits to stabilise them?

I think my glasses need cleaning, or filling, I read that first line as "I've acquired a faulty crutch".

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.

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.

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.

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")

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

To email, substitute .nospam with .gl

According to this website:

HTH

Peter

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:-

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.

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.

.andy

To email, substitute .nospam with .gl

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

To email, substitute .nospam with .gl

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...

About £3.50 - Bargain!! (Unless it's 650 yen each..)

Peter

Sadly it appears to be the unit price. So probably about 40 quid including carriage. I've e-mailed Crotech about spares. ;-)

Have you tried

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.