The reed I was referring to is made by Crydom, offices in USA and UK. Parts available from RS, Farnell, and maybe Crydom themselves if you ring up and ask for experimental samples.
www.Crydom.com or (.co.uk) are the supplier I was referring too.
The only likely candidate is Crydom VDA200GH, approx ?2 each, as shown rightmost in this table :-
http://www.crydom.co.uk/Webpages/sub_and_tiny.htm
http://www.crydom.co.uk/Webpages/reed_s ... _notes.htm
http://www.crydom.co.uk/Webpages/reed_o ... agnets.htm
The magnetic sensitivity / strength / distance is the all important point about this switch, as I believe everything else about makes it the best and only likely replacement part. But it?s also the one point that needs experimenting with. This could be done outside a module, using a pulsar button with the magnetic still within it, and moving it back and forth from 2mm to 8mm from the reed and work out where it closes, and releases again.
As with all things there are ways of expressing the reeds operational performance, and looking at tables of data (as shown in the above links). EG, a reeds sensitivity for closing/opening is rated in ampere-turns (nice and obscure standard), and the distances in MM depends on the magnetic flux rating and shape/orientation of the activating magnet as measured in Micro Webers (even more unfamiliar, but a standard none the less). And using these two ratings and some look up tables it is possible to work out if a reed / magnet is a likely combination. But the one thing I don?t know is the magnetic rating of the magnets used in pulsar buttons. However, anything 3mm long is likely to be similar to currently available 3mm long sub miniature magnets available today. Etc.
But this is all getting a bit OTT for DWF, and in the time I?ve spent writing this I could have ordered one on-line and let you know how the experiment goes within 48 hrs !
The particular reed I mention is the tiniest one they do, needing the smallest amount of magnetic force to activate and release. My gut feeling is that this will do, but to prove the point I need to actually try it out. If it isn?t the one, and you don?t have a dead module with good original reeds, then give up as there are no other modern alternatives !
Off course, I could be wasting my breath, because I bet I know one person who occasionally lurks on the forum who?s been quietly replacing reeds in modules for years, doing an neat excellent and perfect job each time, and making a good income from doing it, and who probably just gets on with it rather than arguing about if it?s the precise absolute 1973 original reed, and couldn?t give a stuff what anyone on here says, because hes been successfully doing it for years !
Heres a pic of pulsar module with 5mm reed :-
And heres a screen grab of the crydom one I would try (but out of stock today !) :-