Look no further than the Calypso IV or Calypso J....These were made by US Divers forever and can be found at swap meets, Craigslist, garage sales, on line auctions for CHEAP. They are a robust no frills regulator that got thousands of divers in the water and can be easily serviced with a few basic hand tools and a little patience.
At the bottom of the page I'll post links to the US Divers service manual and some service notes I made.
Aside from basic hand tools you will need an IP gauge and a few picks to remove internal and external O-rings. Insure that you only use picks made from plastic or brass as damaging sealing surfaces using stainless picks can leave you with a regulator that no longer seals up tight. You can easily make O-ring picks from brass fishhooks of various sizes.
The only worrisome spot on this regulator is it's high pressure seat as it is unique to this model and no longer reproduced. I do have originals but they are not cheap. With a little care and patience you can most likely bring yours back to life.
The US Divers manual calls for an Easy Out from McMaster Carr or Sears to remove the high pressure seat....Seems like a bit of overkill since the only thing holding the seat in place is an O-ring
I have found that a small wood screw with the sharp point ground off works great to remove the seat.
The center of the high pressure seat is a hollow brass cylinder and by turning the screw with my fingers only I can get it to grab just enough to pull the seat straight out.
The center brass cylinder slips out of the nylon section of the seat
Use a piece of 1500 grit or emery paper on a flat surface and slowly move the seat face back and forth you can remove the groove made by the piston. Be sure to go slow and check your work often. Only remove material until the groove is gone.
Be sure to re-assemble the seat and brass cylinder the correct way and lightly lubricate the O-ring around the hp seat. Push it back into place till it seats with a pencil eraser or wood dowel. Do not press on the high pressure seat with metal tools!
The other challenging area of this regulator is the bonnet nut which contain internally the sealing O-ring and backup washer for the piston. In the service kit I have included the traditional PFTE split washer along with the updated version. Either one works fine but the updated one is easier to put in place. When using the updated ring be sure the groove side faces the O-ring Be sure to assemble in the correct order. (follow the manual)
This model was always paired with the tried and true 1085 second stage
which is just as easy to service as the first stage and the service procedures for it are in this manual.
You will find the service kit for the Calypso First Stage and the 1085 second stage (Blue Kit) in the Vintage Double Hose website store.
The Calypso regulator is no substitute for a Double Hose but it is a good choice for a reliable vintage single hose regulator. Your dive buddies may scoff at it's utilitarian features but when their Super Gonkulator titanium 12 heat sink 5 lever greatest regulator ever goes tits up on a dive trip you can slap on your Calypso and go diving.
Pet Peeve 101.....After your first and second stages are serviced and setup you need to actuate the breathing cycle a minimum of 50 times allowing the 1st and 2nd stage seats to get in their groove so to speak and then do a final check of your IP and lever height.
DO NOT tap on the purge button like the Space Invaders FIRE button to do this.....Think about it....Is this how you breathe? If you answered yes, give up diving and take up golf....Breathe from the regulator normally or do many slow light purges of the 2nd stage. Banging on the purge button staccato style accomplishes nothing..
Go seek out a Calypso and have some fun.