Atomic B2 or Scubapro Mk25/A700 Owners: Pro / Cons

[Shabaday]

I have had both of these. I ended up with Atomic ST1 and SP Mk19/G260
Between the two you suggested the B2 with a sealed first stage and yes I always use the fifth port for my long hose exactly like image posted in this thread. I have two ST1 and sold my M1's. I also don't care for the A700 at all. I also prefer a sealed first stage hence the Mk19. The G260 is a beast. Ultimately you will be just fine with whatever you choose.

 

[Nemrod]

I am still using my MK5/109 purchased in 1977 and continiously updated with newer parts.
Nothing surpasses Scubapro in durability and long-term serviceability.
But wanting something more modern, I would choose a MK10 with SPEC boot and sealed and a pair of G250V.
And the DIN conversion kit, of course.

Not an argument, just a curiosity, why would you prefer a Mark 10 and a G250V instead of just jumping to the Mark 25/17/19 and G260?

I find the G260 easier to achieve a very fine adjustment using the Micro-Adjust feature without resorting to my "assorted spring box" to find the perfect spring. The G260 is also outwardly noticeably more compact than the G250 or G250V. I also find that the G260 has a smoother transition from low to high Venturi effect. But saying those things, the G250V is basically a G260 without Micro-Adjust and a "vintage" looking case.





Just curious for educational purpose.

 

[buddhasummer]

For me a plus to the G250V over the G260 is ease of tuning, you don't need a gauge, it can truly be serviced in the field with nothing but a screw driver in less than 8 minutes. I'm not saying the G260 is difficult to tune coz it isn't but the G250V is an in field servicing dream. YMMV.

 

[buddhasummer]

But agree James, fine tuning G260 for the win.

 

[L13]

For me a plus to the G250V over the G260 is ease of tuning, you don't need a gauge, it can truly be serviced in the field with nothing but a screw driver in less than 8 minutes. I'm not saying the G260 is difficult to tune coz it isn't but the G250V is an in field servicing dream. YMMV.

I don't quite follow why tuning is different between them. Is it because you need a hex for the balance chamber course adjust on the 260?

 

[buddhasummer]

G260 has two points of tuning, orifice and micro adjuster. The G250V has only one point of tuning, the orifice. With a G250/V once lever is set what you get is what you get unless you have a bunch of springs to play with, with the G260 you can finely adjust spring pressure using micro adjuster allowing pin point cracking accuracy.

 

[Nemrod]

I don't quite follow why tuning is different between them. Is it because you need a hex for the balance chamber course adjust on the 260?

You are not thinking about this adjustment correctly. The Micro-Adjust is not a course adjustment, it is a micro-adjustment. It adjusts the spring tension which cannot be done on a G250/G250V. The only way to adjust spring tension on those is to try different springs until the perfect one that suits you is found. With the Micro-Adjust the lever is set with the orifice as always and then the spring tension can be adjusted to get the cracking effort where you want it.

The G260 service manaul has a redundant and counter productive series of steps having you readjust the orifice after adjusting the Micro-Adjust. This is, well, essentially WRONG!

Regardless of what Scubapro says (referring to the G260 manual), and very abbreviated here:

1. Set the Micro-Adjust to have a 2mm protrusion and install
2. Set the orifice to get lever height
3. Cycle the regulator as needed to let the LP seat take a set
4. Readjust the orifice until there is a slight leak with the knob full out (Micro-Adjust set with 2mm protrusion)
5. Turn the orifice in 1/16 turn increments until the leak stops (or some let it very slightly leak if about 1/2 turn on the knob will stop it)

Note: The cracking force should be in acceptable specs now but might be on the high side of specification

6. Fine tune adjust cracking force now with the Micro-Adjust (or if a G250 go looking in your box for another spring )

Note: The 2mm setting is important. That is your neutral setting and any adjustments should be made from that neutral position. The 2mm protrusion results in what you would have if there was no Micro-Adjust feature.

Edit to add. When you take your new Scubapro regulator equipped with Micro-Adjust out of it's environmentally friendly recycled cardboard packing that Micro-Adjust is going to be set to 2mm, I betcha. And the regulator is going to breath like cow dung. Am I saying that by default then the G250V breaths like cow dung compared to a well set up G260 ? Not going there, ha! Did they ship them with assorted springs and shims? Do you feel lucky?

 

[L13]

You are not thinking about this adjustment correctly. The Micro-Adjust is not a course adjustment, it is a micro-adjustment. It adjusts the spring tension which cannot be done on a G250/G250V.

Look at the schematic again. The knob on the G250 effects the balance chamber/spring exactly the same way that the Knob/micro-adjust effect the balance chamber/spring in the G260. the micro-adjust just lets you change an offset in the knob positioning of the balance chamber.

Orifice position sets lever height (and if you can even get a seal). Balance chamber position sets cracking pressure (for a given spring).

Yes, you can change the cracking pressure by moving the orifice past the just seals position, but only at the expense of dropping the lever height.

Given all that:

I completely agree with you on the procedure. Just note that steps 4 and 5 basically end up resetting lever height to the highest possible while still sealing.

If done right, steps 1-5 will always set cracking force to the minimum possible for any given spring (G250) or spring/micro-adjust position(G260). trying to go lower, using the orifice, will produce a leak, trying to go higher, with the orifice, will drop the lever. Cracking force is really only properly set by step 6.

 

[Nemrod]

Look at the schematic again. The knob on the G250 effects the balance chamber/spring exactly the same way that the Knob/micro-adjust effect the balance chamber/spring in the G260. the micro-adjust just lets you change an offset in the knob positioning of the balance chamber.

I would agree (all not just my quoted part ) except that the Micro-Adjust is a much finer adjustment than the course adjustment of the knob. And I have encountered a number of G250 that the spring is simply too stiff or too long due to parts stacking (or?). Being able to reduce or increase the M-A protrusion during final adjustment compensates for spring variability.

 

[L13]

I would basically agree (all not just my quoted part ) except that the Micro-Adjust is a much finer adjustment than the course adjustment of the knob.

I agree, I was wrong to call it a course adjust. It basically just adjusts the length of the knob, and has finer threads than the knob.