Was it one of those gigs that got released later on?
The bass sound on "On Stage" is very good, not nasty at all. The two pickup Telecaster I presume.
I really can't say anymore! The Frankfurt gig was not among that trilogy of gigs that got released later on, but it was the same tour. I'm not much of an On Stage fan, it came too early in the bands career (and featured recordings too late in the tour where Cozy Powell later on moaned "my playing was already suffering because I was too knackered"), featured almost nothing off Rising, got released when that particular line up was already history and the production is extremely flat. Strange that Martin Birch who did such great work with Purple, floundered on almost all Rainbow albums he produced: the debut is murky (compare Stormbringer or Come Taste the Band to it, both have aged much better), Rainbow Rising has hardly any bass or keyboards in the end mix, especially the European one (it sounds like Cozy and Ritchie rehearsing with Dio singing to it, the demos sound much better and audibly feature the whole band), even the orchestral parts are way too much in the background, On Stage is flat (compare Made in Europe to it which practically jumps out of the speakers at you, even Last Concert in Japan SOUNDS better, never mind Bolin's flawed performance on it), only Long Live Rock'n'Roll is up to Martin's producton standard. I always wondered whether Blackmore kept Martin Birch on a tighter budget or intervened too much for the production outcomes being so poor.