Re: Thoughts on the New JTM45
The JTM45 is a unique amp. It's certianly not a 4-ten bassman, and the later "plexi" models obviously evolved from the JTM-45.
In terms of comparison to the 5F6A bassman the JTM-45 has these profound differences: Output transformer, Power transformer, KT66 Output Tubes, instead of 5881, Use of ECC83 preamp tubes and PI throughout, instead of 12AY7 for V1, and 12AX7 for others, 16Uf filter caps in the power supply, four times the amount of negative feedback, 12" Celestion speakers instead of ten inch Jensons, and differing cap values determining the Eq slopes of the two channels.
The early solid state rectified (plexi) Marshall amps such as used by Hendrix, Clapton (EC actually owns and uses occasionally an early JTM-45 head), EVH, AC/DC (Angus actually uses a 65 JTM45) ...ect.... are certianly closer to the JTM45 preamp design and power supply, than the 70's four input Marshalls, or JCM800 Marshalls and later. Moreover, many classic "plexi" tones such as used by Duane Alman, Paul Kossof, and Doyle Bramhall II...ect.. are 50 watt 1986, and 1992 model 100watt super bass amps, that continued the JTM45 preamp configuration, and coupling cap values. The JTM45 is a Marshall amp, and Marshall sounding amp, closely associated with the plexi mojo.
The reissue amp obviously can't use exact RS transformers as the early JTM45, and it uses late plexi 50- watt type 50/50 filter cap cans in the power supply. It also uses Russian 5881 tubes, instead of KT66 tubes. Moerover, the bright caps are closer to 68 plexi value than 66 and earlier JTM45. Many people go about modding their re-issues to original spec, and the Mercury Magnetics JTM45 transformers, and choke are popular upgrades. The 65 and 66 JTM45's had plexi panels and started the term plexi......
