Here's a question for you Bri: what are the specs on that output xfmr? Is it a repeater or does it step up/down to go into the mic pre on a 300 series? I'd guess down; in any case my question iwould what's the gain before the output iron swallows it? AND it could be a step up depending on the insertion loss... I dunno.
Let's say we were putting together a circuit to run at line level, maybe even w/an unbalanced out option to take advantage of the unbalanced line in on the 3xx's; 4/1 times two, wouldn't need panpots, we'll add that later.
Any mic input trafo should work fine on the EF86/PF86, Lundahl, Cinemag, what have you; Jensen too for deep pockets; old Beyers for diehard masochists. Let's say our topology is to use the first tube stage in the 3761, mix the signals and use a single make up gain tube stage; would we want interstage iron where the original output iron is, then gain stage and another balanced line out xfrmr? To make the mixer a little more multi-use, and we could switch the output for unbalanced out for the 300 electronics. How much gain do we want to land at, 36db? Less, more?
500K or 1MEG pots aren't that hard to get ahold of, that's elecguitar tone/volume control territory, I've got a gob of 1Meg pots in the parts bucket; wiring 'em in ain't no biggie, we can follow NYDave's lead from his passive summer topology; if the impedances are right (I'm just spitballing here) we could use the final gain stage from J's G7, the SRPP w/the 12 position attenuation switch, or fiddle it enough to get it to work.
More dreamland gunk would be to throw a multipos switch on the mic levels instead of 100K pots, for repeatable settings.
PSU is the last adventure, but as we're not bound to Ampex topology we can either throw the right xfrmr in front of the filtering circuit or just go from scratch; four more tubes of as yet unknown amperage appetites would lead us to chopping one up custom like.
Noise is probably the biggest philosophical concern here; mute switches for unused channels could be good; a dual psu might give us a little less noise, rectified heater supplies could help, shockmounted tubes; effects loop (hook it up to the sofa springs for some boing) could be happy little noggin' scratcher too. Last but hardly least this would have used the mic level on the recorder as the master fader, basically, so we'd need a master level. Add present day bells & whistles like phantom and phase switching it'd be tres goofed. I suppose we'd then need line and instrument in as well, hmm...
Given the latest garroting we gave the 351 mic pre circuit over on the Ampex list, this guy as-is would seem to be of dubious value, unless purpose built for ribbons or dynamics of similar vintage.
I've ne'r heard one; did you plug it in to see what it was like when you were done repairing? As noisy as the MXs?
This would be a fun one I think, albeit a little expensive w/ten xfrmrs. I might try it for the location sound cart.
(I *knew* I'd find you over here eventually; it's good company, dontchya think?)
Brad
[quote author="Brian Roth"]Yes, I suppose something like that will work, BUT it will result in even more signal loss in the mix bus.
Keep in mind, the 3761 mixer was mic level in, mic level out. It was sold as an accessory for the Ampex 300 series recorders, and used the 300's mic pre for makeup gain.
Bri[/quote]
