Help ID'ing Scubapro First Stage Reg

[happy-diver]

Here's a yoke nut de stumpfer with polished jaws

because what you really need is maximum purchase

 

[george_austin]

You may need a bigger hammer

 

[Hethen57]

The giant adjustable wrench approach is a great way to ruin the yoke nut, these things really get stuck on there! So I took on a little side project of cutting down a spare 1” socket and welding it to some flat stock to make the appropriate wrench, snugged it down tight with the thumb screw and it came off without damage. Thanks again.

 

[vjb.knife]

I would say it is the Mark V. I have one that I bought in 1970 and it originally had the two port LP swivel, but around 1975 or 76 I bought the multi port swivel similar to the one you have, but it has more ports. I still have the regulator and all the parts, but it has not been used or serviced in about 35 years. I moved on to a Poseidon Cyklon 300 and then an Odin which I also still have. Now I dive a few others from Scubapro and Poseidon.

 

[Angelo Farina]

If it has not been modified, I would date it at approximately 1978. The 1975 model was my first reg, still in use, and it has just 2 LP ports. It appears unmodified in the 1977 catalogue:
http://www.angelofarina.it/Public/Scubapro/Scubapro-Catalogue-1977.pdf
The 1980 model has smaller holes in flooded chamber, and 5 LP ports, as there is a top one for maximum flow. So your should be a 1978 version, with large holes and no high flow LP port, and a joke not rated for 3000 PSI.
I have four MK5 first stages dating back to 1975-1980 (2 are mines, 2 of my wife), and all are working great. All parts are yet easily available, and Vintage Double Hose can provide ready-to-go service kits.
Only part difficult to find is the 3000 PSI joke (or the DIN conversion kit, which would be even better). On my 1975 model I installed the joke of a Cressi, which is almost identical to Scubapro 3000 PSI, but is rated at 250 bars.
I warmly suggest that you use the MK5 for your 109 2nd stage, and that you upgrade the 109 to a 156 (fully balanced, easier to tune and maintaining the tune for years). Again, Bryan at VDH has the conversion kit. And then downgrade your MK2 as the the first stage of your secondary (being historically correct, that should have been matched with a 108).
Well, of course I prefer to have two MK5 and two 109/156, in practice in our setup there is no clear difference between primary and secondary....

 

[Hethen57]

Thanks for the follow-up replies, it was fully cleaned and serviced and now has a balanced adjustable 156 second and a 108 safe second which both breathe perfectly.

 

[Fibonacci]

The giant adjustable wrench approach is a great way to ruin the yoke nut, these things really get stuck on there! So I took on a little side project of cutting down a spare 1” socket and welding it to some flat stock to make the appropriate wrench, snugged it down tight with the thumb screw and it came off without damage. Thanks again.

A regular socket will still bear on the first few mm each side of the points and gall them if really tight.

The other issue is the small radius that is machined inside the socket means even less surface area to grip the soft thin brass yoke nut.

The best way I found is to use impact wrench sockets, these only have a hex shape inside not multi-points and so bear on the entire flat of the nut.
If you have access to a lathe you can part it off or machine it shorter with carbide inserts.
Otherwise spin the socket against a grinding wheel you can easily remove the inside radius to ensure you get the absolute maximum surface area. File off square and finish with some wet and dry paper on a sheet of plate glass to smooth the surface so it won't scratch the yoke.

Machined regular socket on the left, impact drive socket on the right.