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1989 THD Plexi 50 Boutique Tube Amp Head & 2x12 Cab, Tweed-Covered w/ Celestion Longhorn 12


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Up for sale, a 1989 THD Plexi 50 and matching 2x12 cab in exceptional condition and in perfect working order. Founded in 1986, THD (Total Harmonic Distortion) and their founder, Andy Marshall, has a rich legacy for innovative boutique amplifier design. This early Plexi 50 is akin to Dave Friedman’s “holy grail” Plexi, with two parallel input stages (one channel) that are internally linked, along with a fully tweakable tube-driven effects loop.

This amp succeeds in capturing the smooth, harmonically-rich Plexi tone, delivering both muscular cleans and ripping crunch when cranked. A two-channel affair (again internally linked), the controls are highly sensitive, and small adjustments yield a uniquely broad range of tonal colors. Ideal for the player who likes to have their amp really cooking and dial the amount of gain on tap with the guitar's Volume knob, this Plexi cleans up beautifully and also takes pedals with aplomb. The footswitchable tube-driven effects loop has its own dedicated bank of controls on the underside of the chassis.

Controls include Presence, Bass, Middle, and Treble knobs, along with the two Volume controls. Dialing up the Normal Volume knob will add low end heft to the signal even if the guitar is plugged into the Bright input, and the Treble and Bass EQ knobs are vintage-style “interactive shelving” type controls. The Middle control dictates the potency of the other two EQ knobs; when the Middle control is rolled off, the Treble and Bass have more effect, and when Middle is cranked, the other two EQ knobs have substantially less impact.

The tube complement consists of a matched pair of GrooveTubes 6L6 power tubes, with a matched preamp section of four GrooveTubes 12AX7s. The cabinet is loaded with the original pair of Celestion/THD Longhorn 12” speakers. These speakers are Celestion Lead 80s with a proprietary treatment to break in the cones. Powerful and smooth-sounding, without a lot of coloration, the Lead 80s reproduce the sound of the amp in a true and musical manner.

The tweed on the head and cabinet exhibit only very minor wear, with oxblood/gold stripe grillcloth, a custom metal THD name plaque on the head, leather handle, and nickel cabinet corners.

A printout of the original user manual is included.