Marshalls running low voltage taps ?

[Sigs]

Came across this in another forum, would appreciate Plexi experts thoughts on this-

“In my opinion, which nobody asked for, the biggest fail in most reduced-output "Marshalls" of any type is the fact that when reducing the voltage to the output section, you inevitably reduce the voltages throughout the entire amp which completely alters the sound of the much louder - and higher voltage - amp that you're trying to emulate. A Marshall PI running at 250+ plate volts sounds audibly different from one running at sub-200 volts, for example. And likewise throughout the preamp.”

 

[TAZIN]

From my experience the character of the amp doesn't change that much providing that you re-bias at the new lower voltage AND the lower voltage isn't dramatically different from the normal voltage. For example, if an amp running at normal wall voltage produces a plate voltage (after bias) of 490 Vdc and I compare it to the same amp running a plate voltage of 470 Vdc (after re-biasing) it sounds pretty much the same just a tad less loud. If you go from say 490 Vdc to 350 Vdc plate voltage (biased accordingly) then you'll hear a greater difference.

 

[junk notes]

You are asking to comment on someone else's opinion - in turn he cannot answer posts. Curious, what are you asking actually?

 

[Dblgun]

Marshall produced some amps with lower HT (approx. 380vdc at plates) but also eliminated one of the dropping resistors. In doing so voltages in the remainder of the amp are in line with amps with higher HT. As it relates to 1987/1959 type circuits my experience is PI plate voltages of 250v or greater would be abnormal. Marshall voltage charts for amps of the era you are asking about are typically 190-230 with the exception of the 200W Marshall Major. These voltages would be in the range of what I have found in amps that were healthy. Just my

 

[william vogel]

Eddie Van Halen