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Altec 458 A Preamps?

Member for

20 years 9 months
I am not sure what forum this should go in... I also posted at Advanced Audio...

I'm posting this for a friend that does not have internet access currently... He is doing a project where he's outfitting a new studio for doing live broadcasts of jazz.

Part of the rig will be taking a bunch of old Altec preamp modules (458A's) and racking them up to use as preamps... He is very knowledgeable about tube gear (many of you have probably used his designs), but he has a question.

When looking at the schematics for these guys, it isn't clear in specs if it terminates or bridges mic source. The input is rated at 150 ohm, but neither primary or secondary of transformer does not look resistively loaded. Is it 150 ohms or more?

Anybody know exactly what is going on and has some real experience with these? I hope what I've written makes sense (as I don't have a large technical knowledge of this stuff). Any help would be *greatly* appreciated.