During 1958, Fender introduced the model 5F6-A Bassman model. This final 1950s Tweed Bassman model product line included a change from the 83 mercury vapor rectifier tube to the GZ34 rectifier tube, as well as a modification within the Presence control circuit. During early 1960, Fender began producing the 5F6-A Bassman with Jensen P10Q speakers. The P10Q speakers handle more power and produce better "clean" tones than the earlier P10R speakers. The P10R speakers were shipped within all Fender Bassman amps from late 1954 until early 1960. Many professional music industry analysts have proclaimed 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. Several Bassman models were progressively influenced by the 5D6 through the last Fender Tweed 5F6-A Bassman's circuit design. The 5F6-A Bassman's design was directly copied by Marshall Amplifiers in their JTM-45 amplifier during the early 1960s.