Dating drake transformers
These amps run at much lower voltages than the later KT66 amps, producing less power while being easier on the tubes.Also, it should be kept in mind that the voltages drop or sag significantly under load, since the power transformer was only rated for 200m A (by comparison, a Twin transformer is 450m A).The early ones had ohms switches mounted to the transformers, whereas the later ones had ohms switches on the backplates like later amps had.The transformer was the same Drake 784-103 used in the 1965-66 JTM45s, although two transformers was used for a quad of KT66s.This article tries to give an overview over the early Marshall 100 watt amplifiers by piecing together available information and shedding new light on transitional models from 1967. Finally, the JMP plexi faceplate replaced the earlier faceplates.The first 100 watt amps known today as JTM45/100s used JTM45 plexi faceplates and white Super 100 Amplifier back-plates. The main stages in the evolution of these early 100 watt amps are Whos Pete Townsend.These 100W amps are basically like a dual JTM45 but with a solid state rectifier, giving slightly higher voltages.Whereas a JTM45 puts out 30-35 watt at the point of breakup, these early amps put out around 70 watt at the point of breakup (and more than 100 watt at full breakup).
The head cabinet on these amps use two narrow Vox type vents (used until late 1966).However, the 100 watt PA amps used JTM100 faceplates. First, the plexi Superlead and Superbass backplates were introduced, then the so-called Black Flag J. The first prototype is reported to have used four 6V6 output tubes and a single GZ34 rectifier tube.It probably used only one Radiospares Deluxe Output transformer, reportedly giving an output of 60 watt.This high resistance gives more voltage drop across the choke than with the later chokes.When running the amp hard, screen voltages (and preamp voltages) will sag more, giving a softer response with more A key element to element to the sound and response of these amps lies in the power supply, especially the filtering (smoothing).