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In Reply to: RE: Just rebuilt posted by unclestu on May 11, 2014 at 20:29:34
Agreed. The original Stereo 70 design in proper working order is still a very fine amp, especially with the playing field leveled by some enhancements like a beefed-up power supply and improved parts.
Follow Ups:
I have two redone ST-70s, one has the high voltage German can cap and the Tubes4hifi 12AU7 input board using Russian PIO coupling caps. The other one has the original 7199 circuit on a new input board with new parts and the Triode mondo power transformer and Curcio discete cap board.
So, essentially, one has the original power supply and redone input board and the other one has a much stiffer power supply but the original input board. One sounds much better than the other, and that one is the one with the improved power supply. Go figgur.
Vale amplifies run at high supply voltages.
PSU energy storage of a capacitor power supply is half the total capacitance times the voltage squared.
So, valve amps will respond strongly to PSU storage upgrades. Esp. if the rectification limits are addressed. If the VR is replaced then the storage of the supply is only limited by the PT's heat limits.
Using good soft-recovery SS diodes will also raise the available voltage. While this may not look like much - the same factor of high voltages - makes it worth having. The benefit of say 15v of HT is not small, even in a ~20wpc pp power amplifier. e.g 300V original (off the VR) squared is 90,000, but 315V is not 90,00 plus 15 squared (90,225) but 99,225.
Nearly free lunches are rare.
A small valve amp can IME have far better bass than even a big DRY-bass SS amp. Valve bass but with SS slam and control.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
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