You can always easily replace the ignitor (starter) they are replaceable......keep the same ballast but replace the starter....

i am keeping the 70 Watt HPS ballast....the ignitor crapped out on me so i gotta find a new one!

The ignitor already crapped out? You have been doing too many experiments with this ballast.

its a Chineese Ignitor,so what do you expect? ....i only ran that 100 watt Merc in it one time..and i did stick a 60 Watt incandescent lamp in the socket to see what it would do....it was gonna go out eventually,the ignitor is just an extra part to go bad....i will get a much better ignitor...and replace that Crappy Polor Lights lamp.

Lol yeah those Chinese ignitors . I had the same situation with a 70W HPS Castor ballast and ignitor,the ignitor lasted about 8 months,I replaced it with a good quality Advance ignitor.

The MV will wear a lot, because cycling and there is an additional risk you start and arc outside the arc-tube due to high voltage from the ignitor during hot-restrike attempts...
In Europe, as the SON/MH70W is 1A/77V (the US one 1.5A/55V) work well the setup using SON70W ballast, it gives 0.9A to the MV100 (spec is 0.95 if i remember well). As EU SON70W have the same spec as pulse-start MH70W and these are the same worldwide (1A/77V), i think the "pulse-start MH70W" (i'm not familiar with ANSI numbering) HX ballast with disconnected ignitor will work (OCV around 230V, forcing 1A into 77V lamp, so it should force 0.9A into 130V lamp)...

i dont think the risk of an arc forming outside the arctube is all that great,the ignitor does not provide enough current to strike an arc in the outter bulb,not saying it isnt possible,as little weak,nearly invisable streamers do form between two pieces of the frame,but nothing damaging,like melting the frame.

Ignitor crapped out huh?  Sounds like a Caster to me 

the 70 W Ballast is a Caster,the ignitor has no labels that identify Brand,but its probably a caster.....the ballast is actually really good,it runs nice and cool!

My Castor ignitor is a white square one,if yours is like that it would be a Caster as well.

yep...its a square white plastic casing.

My cooper fixture also had a crap igniter. It lasted three years since it was installed in 2012 and it died bout a week ago. I noticed it had trouble starting so once it died I gutted it and installed my 100w merc ballast. It looks a lot like an authentic NEMA 175w bucket lite, but scaled down a bit. 

I have a Lithonia (Chinese built-has Caster components)100W MH light whose igniter failed-runs 100W mercury lamps just fine-rescued from the junkbox!