Specs:

  • Classic "Plexi" circuit
  • 2X 6V6S output section
  • 5AR4 tube rectifier
  • PPIMV for cranked sound at low volumes
  • Channels internally jumpered
  • Front panel bright switch
  • "Deep" switch for 2nd stage cathode cap
  • 6V6 Plexi

    Please see the new and improved version of this amp. the Plexi Jr.

    This amp is a 20 watt version of the classic plexi circuit. It uses 2 of the very robust JJ 6V6S output tubes. It is tube rectified with a 5AR4 which adds some compression. The transformers are Deluxe Reverb replacements from Weber.

    It is hand wired with PTFE insulated wire and uses only high quality components. BTW, this means there are no carbon composition resistors, they are noisy and they drift in value. The board material is glass epoxy which will not absorb moisture unlike other materials that are sometimes used like phenolic.

    The normal and treble channels are internally jumpered and each can be turned on or off via a rear panel switch. This is commonly done with a patch cable by users of this type of amp to increase the gain, but the real benefit of doing this is that you can dial in some low-end response at all gain levels. As can be seen above, only one input jack is used and is wired directly to the input jack switching via a piece of shielded PTFE cable, this helps reduce noise and is a standard practice of many boutique amp makers.

    The "Deep" switch allows you to switch a .68U capacitor in or out of the circuit on the cathode of the second gain stage. This increases the gain and slightly changes the frequency response and is a common mod to do to this circuit.

    PPIMV - Post Phase Inverter Master Volume. Another common mod done to this type of amp. This allows you to max out the preamp volume but to still play the amp at bedroom levels ( or gig levels for that matter). By the way, don't let the 20 watt rating fool you, this amp is loud. It's too technical for a full explanation, but suffice it to say that because of the way human ears hear you need 5 times the watts to get double the volume. So, a 100 watt amp is only twice as loud as a 20 watt amp, not five times.

    The front panel bright switch allows you to switch between a 500p and 100p bright cap, or to have no bright cap in the circuit at all. 500 picofarads is the value often seen in this type of amp, but it can sound harsh at lower volume settings or with certain guitars. 100 picofarads is the value found in the old 5F6-A circuit that this amp evolved from. Some players also prefer no bright cap, so I made this an option as well.

    If you would like to have an amp custom made for you, please use the "contact" link at the top of this page to send me an e mail.

    Schematic

    Song I recorded using the amp

    Sound clips :

    These clips were recorded with a Jackson solidbody with a Seymour Duncan JB humbucker in the bridge position. 'JB H B" means humbucker mode, "JB PSC" means I flipped the switch that changes the pickup from a humbucker to 2 single coils in parallel. The PSC mode has less output and is more single coil sounding. "N and T" refer to the level the volume was set at for the normal and treble channels . The "Deep" switch is on, the "bright" switch is at 100 picofarads, and the "Master Volume" is set at about 2 on all of the clips. The speaker cabinet is an Avatar open backed 2 X 12 loaded with a Celestion Vintage 30 and a Celestion G12H. The cabinet was miked close with a Sure beta 57 and also a condenser mic facing away from the cabinet for room ambience.

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