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Stephenson Amplification

Dual-Plexi Amplifier

Deluxe Amp


  • Two voices selectable from front panel gain switch. Lower gain 1965 Parks specs, and higher gain 1968 Marshall specs.
  • Single input that internally jumpers the 2 channels together. Normal volume and Bright volume are both always active.
  • Cut switch (front panel).
  • Drive control.
  • Power Scale master wattage.
  • Foot switchable boost.
  • EQ bypass when boost is activated (rear panel switch).
  • Tube buffered effects loop with foot switchable bypass.
  • Custom Made in Canada toroidal transformers.
  • 3 tube power amp.
  • Ultralinear option (rear panel switch).
  • Aluminum chassis with welded seams.

Front Panel

Front-Panel Items:

Gain - Normal - Bright - Treble - Mid - Bass - Drive - Cut - Fat - Power Scale - On/Off

Custom Amp Front Panel (1)

Gain, Normal and Bright

  • Gain switch toggles between 2 voices. Up position is the higher gain setting.
  • Normal and Bright are in parallel and both are always active. Normal has more bass. Bright has more gain and more focus.
  • Dial in the desired amount of gain with the Bright volume, then blend in the desired amount of bass (fulness) with the Normal Volume.

EQ Section 


  • Drive controls the signal fed to the effects loop and power amp section.
  • The Cut switch works in conjunction with the Drive control.
  • The lower the Drive control is set, the more impact the Cut switch has.
  • The Cut switch is especially useful at lower volume settings when a thicker tone is desired.


  • Fat controls the body and gain of the power amp.

Power Scale

  • Power Scale is the wattage control system licensed under agreement with London Power.
  • Here is an example of a couple of settings:
    • Full setting = max wattage (30 watts)
    • ½ setting = 8 watts
    • ¼ setting = 1 watt

Rear Panel Features

Rear-Panel Items:

AC input – Ultra switch – Foot Switch jack - Valve select – Speaker output – Effects loop

Ultralinear Switch & Foot Switch Socket:

  • Ultralinear is a 50’s hi-fi type of sound that simulates triode operation. The output transformer has a special set of taps for ultralinear operation. The switch toggles between the triode sound and the standard Marshall sound.
  • The footswitch jack is a ¼ inch stereo connector.
  • The foot switch controls the internal boost and the effects loop

Power Amp Valve Select:



  • This is the speaker output section.
  • The Impedance selector is labelled 1-2-3 since the amp can accommodate different types of power tubes. Depending on what tubes are being used and what tubes are turned on will determine what setting sounds best.
  • When using EL34’s and the EL84 turned off, I think of this selector as 4-8-16.
  • When using a pair of 6V6’s and the EL84 turned off, I think of this selector as 8-16-32.

Effects Loop:

  • Dial in the Send to a level that does not overload the effects unit.
  • Dial in the Return to bring the overall effects volume to the desired level.

Effects Loop Mode of Operation

EQ Bypass Switch


The top row of tubes are as follows:

  • Top right closest to input jack. 12AX7 for preamp.
  • 2nd tube from input jack. 12AX7 for the EQ.
  • 3rd tube from input jack. 6SN7 for the effects loop.
  • 4th tube from input jack. 6SN7 for phase inverter

These are the power tubes.

  • The 9 pin socket on the left is for the EL84. It’s back panel on/off switch is labelled EL84.
  • The middle socket is an 8pin octal type and can run a variety of power tubes. It’s back panel on/off switch is labelled V-2
  • The 8 pin octal socket located on the right side can also run a variety of power tube types. It’s back panel on/off switch is labelled V-3.

Interested in a Dual-Plexi Amplifier? See our Price Page for ordering information!