Welcome to the world of DH diving.
Like Jim said, they are different, don't expect to just stick one on your BC and expect it to work well.....it will work but odds are you will not like it. A DH reg really needs the proper BP to get the best out of it. Do a search here and on VDH, myself and others have posted a lot on diving with DH regs over the years. I think Fred -8dust is in your neck of the woods, if he is close by he would be a great resource. Jim's suggestion on going to Portage is a really good one, some of the most active DH divers in the country will be there and knowing a lot of them personally, I am sure they would be happy to help you out. I love diving the old regs and encourage divers to try them but you do need to understand there is a learning curve and some different procedures that you need to understand to get the most enjoyment out of them.
I would limit your search for your first reg to 2 choices, the DA Aquamaster (aka DAAM- might as well start learning the acronyms
) and the Royal Aquamaster (RAM). Those are the most common, easiest to get parts for, least cost and you can modify them with lots of goodies if you so choose later. Both are solid dependable regs that I have no problems taking to 100ft +. There are other great regs out there but they tend to cost more, Voits for example and with others, parts are harder to come by - Dacors, Healthways and Nemrods for example. One thing I have noticed is the later DAAMs and RAMs (70-72 models) that have the round labels tend to sell for a lot more than the square labels.....beats the dickens out of me why, they are the same reg inside as the older square label ones and personally, I think the older square label looks better. The point being, don't bid up a round label thinking it's better, it's not.
To KD8's list I would add a duckbill and hose clamps. I can about promise you the duckbill is shot in any reg you get. Unless you know exactly who the seller is, don't believe any of the "I hooked it up to a tank and it's in prefect working order" BS. Unless it has been gone through in the past few years I can pretty much promise you it's not in diving shape. To my knowledge, there are only 2 places in the US that still service the old regs so I also don't believe the " it was checked by a LDS and its good to go".
Another consideration is how you are going to handle gas management ? These old regs do not have HP ports so just hooking an SPG to them is not an option. You have 3 options, just use a tank with a J valve, use a tank with a SPG port (some old valves have this option) or use a banjo. Of these options, a banjo is the easiest if you swap tanks a lot. A banjo is an adapter that connects between the tank valve and the reg, allowing you to tap into the HP gas and use a SPG. Using a banjo requires the reg to have a certain kind of yoke. These are at times hard to come by unless the reg already has one but like anything else, there are options if you know where to look and who to ask.
---------- Post Merged at 05:26 PM ---------- Previous Post was at 05:20 PM ----------
i already service my own regulators as is. I know some of the new stuff that is out is nice but way over engineered. I have the new MK25/S600 scubapro but honestly cant tell any difference at 140 foot from my MK5/R109 unbalanced. I have dove these as independent doubles just to check the difference. I have always believed simple is better. Im ready to make the plunge but i just wanna make sure i get something that for one i can find parts for and one that preferably i can have a way to use a spg and an octo.
Most of us just dive old school and use neither- J valve works fine. The only way to go with all that is to add a Phoenix to a DA or RAM.
---------- Post Merged at 05:12 PM ---------- Previous Post was at 05:02 PM ----------
Oh and i was wondering if it was ok to use these on 3000 psi tanks as well?
The old yokes were not rated for 3000 but they seem to work fine at that pressure- at least DA and RAMs, the single stage regs like the Mistral don't work as well with the higher pressure. If you add a Phoenix, it's a non-issue, it comes with a 4k yoke. 
