1991 THD Electronics 4-10 Amplifier

In the pantheon of bass amplifiers, the 1959 “narrow panel” Fender Bassman reigns supreme. The original is beloved by bass and guitar players alike for the combination of power, clarity and crunch available from this design. Over the ensuing decades, there have been numerous attempts by various manufacturers to recreate the original design. In the 1990’s THD Electronics created one of the more interesting updates, with the goal of preserving the best characteristics of the original, while updating the design with a few well chosen modern features. 

Outwardly, the cabinet is a very faithful reproduction, with the original cotton twill (known colloquially as ‘tweed’) covering a narrow panel cabinet. Four cabinet wheels are provided for ease of transport, while the leather handle on top will be familiar to Fender fans. The top mounted control panel is a faithful reproduction, with silk screen lettering over a chrome finish. The design even retains the original style Daca-Ware ‘chicken head’ knobs and a ground switch which is non functional, but added for authenticity. The electronics chassis is robustly made of 14 gauge heavily chrome plated steel. 

A big difference between the THD and the original design is a change from point to point wiring to a printed circuit board (PCB) construction. In this case, it's a conscious choice based on the availability of the highest quality parts, chosen for reliability and design flexibility. The components within are chosen for their tight electrical tolerances and long-term durability: 1% metal film resistors, silver-mica capacitors, metalized film capacitors and 5 watt screen resistors. These components are electrically matched and designed to replicate a circuit that is largely unchanged from the 1959 original. 

It is powered through a pair of 6L6 tubes for a total of 40 watts. Four Celestion G10-L speakers provide sound. There is a solid state rectifier instead of tube rectification, though an interesting choice has been designed into the circuitry. There is a switch allowing for the addition or subtraction of a tone shaping circuit. If engaged, the rectifier will mimic the tone characteristics of the 1950’s tube rectified sound. If disengaged, the rectifier acts as a normal modern solid state rectifier. 

Another modern convenience is an all-tube active effects loop. The input and output jacks for the loop are mounted at the center of the control panel. This loop can be switched on when pedals are engaged and switched off if no effects are used. The off position returns the amplifier to the 1959-style circuit. 

The amplifier is in perfect working order and it is cosmetically very clean with only a few scuffs and rub marks in the tweed, most notably on the bottom strip of the narrow panel frame. Lots of crunch, lots of presence and a nice warm tube sound for bass and guitar alike.