Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jrudi on June 21, 2020, 08:03:42 pm
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Newbie post:
Many years ago, I purchased two used Northern Electric mic pre chassis (no pwr supply nor 70v output ckt) with the intent of "someday"... Well, someday is here, and I realize I can use some sage advice (or thyme advice, if you prefer).
The units no longer have input xfmrs, so I was considering using Altec 1588B transformer/preamp modules in their place, which I have some experience with. Even though I had my original training with vacuum tubes, I have never done anything of significance with them.
It has occurred to me, that the 1588B's could produce too much gain - rated @ 35dBm gain, standard; up to 50 dB with the Ned Clayton mods - for the input to a 12AX7, as I understand that the AX7's are usually used in low-level circuits.
I suppose I could modify the gain of the 1588's down, but what is a reasonable input level for a 12AX7? And at what point does this become a fool's errand; or is it already one?
Any and all thoughts appreciated.
Jeff
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Welcome.
> at what point does this become a fool's errand
When we try to give advice on an un-specified and probably obscure preamp without info or plans. *Which* Northern preamp? "70V output"?? "35dBm" is a level not a gain; typo?