Strand STM Dimmer modules

[tlc]

We still run 90 channels of old STM dimmers

 

We have blown a few of them and need to replace the thyristors (SCR).

 

The original semiconductors are no longer available.

 

Any one have a type number for a suitable replacement.

(UK source preferred e.g. RS)

[Tomo]

Do you know the number of the existing components?

 

If you call Farnell's technical helpline they may be able to find you an equivalent part.

If not, you should at least be able to find the specs for the existing unit, and have a look through RS and Farnell's catalogues for something that will do the job.

[Brian]

If you have trouble tracking down a replacement number I have one of those huge semiconductor cross-reference books here.

[tlc]

I have tried to track down the specs on the original thyristors but to no avail.

 

 

The original semiconductors were manufactured by AEI

 

part no AEI 7546 the case is also marked RS 25

[Brian]

7546 is almost certainly the date of manufacture, 46th week of 1975.

 

So RS 25 would appear to be the part number. The trouble is that I can find no reference to a RS 25 thyristor. Might be worth having a look at a couple of other modules for a different number?

 

There are some STM modules on ebay at the moment.

STM modules on ebay

[RGB]

I've know mini2 racks with triacs replacing the tyristors

Don't know any details sorry, one of those clever types did the conversion and wittered things about 20A triacs and a diode, it was a long time ago

There must be someone clever out there who can work this out

I think I still have stm cct diagrams

[Mush]

Any SCR with high enough voltage and current ratings will probably work,, exception being things that need sensitive gate SCR, that is more usually disco gear with C106 sensitive gate 4A thyristors,but vaguely remember Strand dimmers being TO 48 or similar stud anode package:

 

http://www.cyfronika.com.pl/SEMI/viiiark3p4b.htm

 

First pic found, stud anode less common with, hockey puck, solid state relays ,SSRs , power cubes whatever, all in one package.Not a drop in replacement though because probably pulse transformer triggered.

 

Triacs are what everyone uses nowadays their tougher than they used to be, buy snubberless, isolated tab 600V+ 20A+ , a whole lot cheaper than stud anode SCRs or SSRs.

 

http://www.rapidelectronics.co.uk/rkmain.a...29809&XPAGENO=1

 

Can`t remeber off hand how you would want to wire what will be a centre tapped pulse transformer with each end of winding going to each gate of SCR and centre tap to neutral, to a triac. Don`t want a negative going trigger to the triac. er , mebbe someone lelse can fill in the blanks, Brian...?

[RGB]

One thing to remember if you are contemplating replacing the scr is that the metal side are live! Unfortunately the little stickers telling you this don't last as long as the dimmers!

[Richard Bunting]

You might want to talk to Iain Dennis at www.usedlighting.co.uk, as they have just taken the last of our rental STM racks.

 

Richard Bunting

PRG Europe

[Dave]

At the risk of stating the obvious, have you tried contacting Strand??

 

I have some old Strand spares catalogues and the SCRs used in STMs are the same as used in Tempus and Permus (10A or 25A according to channel rating).

 

As has been previously stated, it's likely that most regular SCRs of appropriate rating will work

 

As an interesting note, I think it's now standard practice to use over-rated devices in dimmers - a 25A triac is common in a 10A dimmer. This means less heat dissipation (=smaller heatsinks=smaller and lighter dimmers), and hopefully less chance of them failing due to surges when lamps blow. I guess that power semiconductors were a lot dearer in years gone by and it wasn't economical to over-spec them.

 

Dave

[Brian]

We still run 90 channels of old STM dimmers. We have blown a few of them and need to replace the thyristors (SCR). The original semiconductors are no longer available.

 

Any one have a type number for a suitable replacement. (UK source preferred e.g. RS)

 

The Service Company, aka White Light, list spare pairs of STM thyristors, part code STM25THY at www.serviceco.com

 

As others have said you could replace with triacs but why bother? Thyristors are still widely available.

 

As a guess, from the old AEI part number (RS25) and the ServiceCo part numer (STM25THY) I'd think we're talking 25A parts here, which is actually the sort of rating I'd expect. A quick look in Farnell shows a few possibles, going with 600v parts in a TO48 stud package we get number...

 

10RIA60 stock code 394-1700 at £5.38 this is a 10A thermal, 25A rms device

 

within that range are a whole load of devices with other ratings.

[johnhuson]

There are some 10 channel racks of STM dimmers for sale at www.usedlighting.co.uk for £100 each. Might be of some help to you.

[benweblight]

stms are analouge are they?

[Jivemaster]

If they're stud mounted check the mounting hardware (washers insulators etc ) and mind the transition from UNC to metric hope its nuts not tapped heatsinks!!.

[benweblight]

can I make an adapter for 37pin soca to whatever it is in the behringer (sub din, it says it has 12ch dimming)