Variacs-VanHalen-Mojo

[BIG Dave]

And to think, EVH was telling everyone back in the 80's he was turning up the Variac to 130V. Glad I never tried that!

[guitar-rocker]

So I just read over on the Van Halen Variac thread- By lowering the voltage to about 90 volts AC you get to the "sweet spot" in tone nirvana; on a Marshall.

Begs the question- Why not simply build the power supply B+ to output whatever the 90 VAC input would result in? Or does it have something to do with the field in the power transformer designed for 120 or 220 VAC that is running 90 VAC?

silverfox.

I've built that idea in a cathode bias EL34 amp, had a PT custom wound to achieve those desired lower B+ voltages. I'm not saying it's EVH in a box, but it does get very brown tones, and the filaments run at the proper voltages, so yes it can be done. The watts are considerably lower though.

[John_P_WI]

You guys are waaaay over thinking this, a simple mosfet pass regulator can easily be configured to vary the B+ voltage, or even simpler - power scale the whole amp. More "brown" comes from lowering the preamp voltages than the power tubes. Play with lowering the preamp voltages 25 to 30% to start and boost the front end.

Oh, having Ted Templeman work his studio magic helps too....

[strelok]

https://www.youtube.com/watch?v=9_ae1P9w4Hw

This video gives a pretty good demonstration of the effects of lowering the B+ as well. Its a duel tapped PT first half is at the normal ~500v and then at 400v. IMO having the right amp into the right speakers totally dimed gets you 90% of the way there, at least for the Fair Warning tone. The lower voltage makes a difference but its quite subtle.