The P10Q Jensen speakers are more able to manage stronger electrical input power and generate better "clean" output sounds than previous installed P10R Jensen speakers.The P10R Jensen speakers were shipped within all Fender Bassmen from late 1954 until early 1960.This model also had four Jensen P10R speakers, but the power supply was redesigned around a single 83 mercury vapor rectifier tube, and a new preamp circuit was introduced that included a three knob tone stack, with separate controls for Treble, Mid and Bass.The power amp included a "long tailed pair" phase inverter, an innovation that noticeably increased the "headroom" or clean power output capability of the amplifier.Many professional music industry analysts have heralded the 1950s Fender 4×10 Bassman amps as the greatest guitar amp ever.The first 1954 Fender Tweed 5D6 4×10 circuit generated further Tweed Bassman amplifier development through 1960.The 5E6-A Bassman model was introduced later that year and included some evolutionary improvements.In July 1957, Fender introduced the model 5F6 Bassman.
Besides being a popular and important amplifier in its own right, the Bassman also became the foundation on which Marshall and other companies built their high-gain tube amplifiers.
Later on, production was moved to Ensenada, Baja California, and the model name was altered to "59 Bassman LTD".
The LTD came equipped with the original 5AR4 rectifier tube, and four Jensen P10R reissue alnico speakers, which was period correct for the original amp.
The output was 50 watts at 8 ohm into a single 12 inch speaker, with a "Tone Ring" baffle in the speaker cabinet.
In early 1961, model 6G6-A was introduced with a solid state rectifier replacing the GZ34, and two 12 inch speakers with a conventional baffle in a slightly larger cabinet (wired in parallel) with a 4 ohm output.