Mats A wrote:Ok i have a 1959 type plexi with EL34´s. The JTM have almost the same preamp as the 1959 excpt for a slight difference in the tonestack and maybe some other minor things. It also have a valve rectifier and hasn´t it got 6L6 valves? Might be wrong on this but was the JTM45 ever a plexi? It must have been discontinued in ´65 or`66.
On my VM 50W there is very little distortion even with the body and detail on full when it´s dimed. I play a Les Paul wich is quite powerfull also.
Different 1959's have significantly different amounts of gain, mainly due to whether a capacitor across the cathode resistor of the V2 voltage gain side is there or not. The earliest 1959's had this cap, but then it was removed for many years until certain reissues came out with them in the late 1990's. EVH's "Plexi" is supposed to have a cap installed in that position, one of the reasons his amp had so much gain.
The preamp in the VM (except for the power supply and a few other changes) is somewhat close to a 1959, but there are a few differences that tend to lower the gain. First, there is no bright cap across the bright channel volume pot (Detail). Also the mid boost circuit removes some gain unless it is switched in. Add a bright cap across VR2, switch the mid boost on, remove C7, and add a 0.1uF cap across R17 (the equivalent of the V2 cathode resistor), and the gain levels of a VM in LDR would be comparable to a "hot" 1959.
You could probably not tweak HDR to sound exactly like LDR, as there is a bit of tonal shaping in the boost stage.