the AnalogRules.com Ampex 351 tube electronics MODs


Information and Tips for using the Ampex tube 350 and 351 electronics as a tube Mic pre-amp



I do a set of Mods on the Ampex 351 electronics.

So far I've done 20 of them for various studios

The mods make a stock Ampex 351 into MUCH BETTER
and far more Versatile - and better sounding
great VINTAGE Tube Mic Pre-Amp

Description of what is done to my modded 351s



These mods REMOVE the recording function of the Ampex 351 Electronics

You're never going to be using these units as a Tape Recorder electronics anyway !


1)   the Old and DANGERIOUS Stock AC connector is removed
and a standard IEC AC Connector is installed,
and the unit is properly Grounded.
A rear mounted AC Fuse is installed.

2)   Various Rear connectors are removed or disconnected

3)   The Record function is disconnected.

4)   The 351 is Modded to have a front switchable Mic - Line Pad

5)   The 351 is Modded to have a front switchable Phase Reverse

6)   The 351 is Modded to have a front switchable one or two stage Low Cut EQ

6)   The 351 is Modded to have a front switchable Second Tube stage Level gain Pot
this allows you to OVERDRIVE one or both Tube stages !

7)   The 351 is Modded to be quieter than the stock unit is, with reduced 60 Hz hum levels as well.
  Non-used circuits are disconnected to reduce noise and distortion.
  All switches are cleaned, connections cleaned, some old wiring is replaced as needed.
  The VU Meter is protected from serverly over-driven signals....
as engineers love to slam the Tube stages !
  Power supply Caps are replaced and upgraded if they do not meet specs
  - some as still in great condition, but most require replacement.
  Caps in the audio circuit are replaced with upgraded Caps.
  Plus More mods done... such as adding Mu Metal in areas to reduce 60 Hz hum.

8)   A front switchable 48 volt Phantom Power supply can be installed

9)   the Front panel is removed and cleaned and polished.
  The original VINTAGE knobs are left in the unit of course !


Complete 351 manual  
this manual is at our Ampex Manuals link - scroll thru the Ampex page


Pictures of various 350 and 351 Electronics



Note:   In all cases you MUST have a qualified tech
change the original AC connector on
the 351 or 350 to a standard IEC grounded cable,
and properly ground the chassis.

Have your Tech also disconnect the Rear 'Jones Plug' wiring
as it has LIVE AC on it !!!

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