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Stephenson Amplification

Dual-Plexi Amplifier

Deluxe Amp

Features:

  • 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 

  • 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 

  • 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:

 

Output:

  • 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

Chassis

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!