• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Ampex Plug-In Mic Pre 96440-02 Schematic and Pics

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Schematic and photos of an Ampex 96440-02 Microphone Preamplifier plugin unit are posted here:

Ampex Mic Pre Plugin 96440-02 | Flickr

An externally hosted image should be here but it was not working when we last tested it.

This preamp uses an unmarked Beyer Dynamic input transformer and RCA Nuvistor tubes, housed in an octal-based aluminum can enclosure. It looks similar to the 96440-04 preamp for the Ampex 354, but it uses different tubes and is not listed as an option on the Ampex literature I found for the 354.

DC voltage supply resistor/capacitor comes from the 354 schematic, assuming this model preamp is compatible.
Well, ****. flickr won't let me download this and there is no diyaudio image.
I have a collection of 7895 nuvistor tubes in boxes from some ancient trash bin. Now if I could find a socket that would connect to them . . .
I wonder if these were the style tubes that were in the air-burst artillery shells and prox anti-aircraft rounds at the end of WWII? A wartime secret never revealed.


Joined 2003
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Yes, Flikyer is a pain.

Consumer Nuvistors appeared in the late 1950s specifically for low-snow high-gain VHF reception for better fringe-area reception (and sales). Yes, they may have been based on military research. I've never seen that documented.

I've seen the same can but with transistors. I suspect it was originally a can for optional input transformers. Stuffing TO-18 was tight; stuffing tubes is amazing (and hot!).


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Sorry, I don't often have much time to post, and hadn't taken the time to look up how to attach files. They are attached here.


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This was an impressively tight build !
Any opinions about it's quality as microphone amp ? Most if not all the parts are possible to source today..

I haven't tried it yet. I don't have a deck to plug it into, so I reverse engineered it in order to rack it up with power supply, line amp and attenuators. I've been curious for decades about nuvistors in audio applications. Back in the day, the RCA TVs with nuvistor front ends said "New Vista Color" on them.
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