Variacs-VanHalen-Mojo

[SilverFox]

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.

[cbass]

Well plugging into a variac will also lower the heater voltage . that will affect the tone some

[SilverFox]

I think that is likely more to influence the change in tone since the various MV and in particular the London Power B+ circuit, from what I've read, doesn't create the Van Halen effect.

What would be the implications of a smaller, less energetic charge cloud near the cathode? Better control of the noise factor? Better energy control? A much smoother sound? This would be a relatively simple mod/experiment.

silverfox.

[jelle]

Does van halen sound smooth to you?

[RWood]

I did it and I didn't sound like Eddie Van Halen, so there is simply no truth to it at all...must be pure myth!

[roberto]

^ this.

[pdf64]

What would be the implications of a smaller, less energetic charge cloud near the cathode?

Possibly not significant.
As the VB+, and so the IB+ would be reduced by the same proportion, therefore less demand on the cathode's output of electrons.

From http://www.valvewizard.co.uk/heater.html
Voltage considerations: The heater voltage specified in the data sheet is the optimum value (usually specified as +/- 10%). Running them at higher voltages will reduce valve lifespan and should be avoided. Running them at lower voltages, within reason, will increase their lifespan and reduce hum. However, if they are run too low then emission will suffer. Running heaters under-voltage is therefore perfectly acceptable. Heaters rated at 6.3V can be run quite happily between 5.7V and 6.9V

[billyoung]

i think there is a youtube video of mike soldano talking about retubing one of the famous evh marshalls. I guess many speculated which mods it had, so he was anxious to see inside. To his surprise he says it was bone stock. Once he finished biasing etc. . He then used a variac to see about its tone, he said at 90 or so volts it got the famous brown sound. I know alot has to due with the guitarist themself, found it real curious that the "Big Mystery" was no mystery at all !!
Bill

[SilverFox]

For what it's worth, here is an actual test that may be legit. Starts around 2:16/

https://www.youtube.com/watch?v=F2NB5bbg6bY

Here is someone else with quite an effects chain and the variac. See for sure the 3 sound samples found on soundckick located in the description as there is a side by side comparison with the actual album.

https://www.youtube.com/watch?v=klC5Od1KIcQ

I don't have a dog in this fight, just so everyone knows. This is strictly a academic question for me..

silverfox.

[RWood]

I did it and I didn't sound like Eddie Van Halen, so there is simply no truth to it at all...must be pure myth!

^Not too big to admit my playing and amp building are both lacking!
Seriously though, I just finished a 20v bucking tranny built into a computer power supply housing. It dropped 120v to 98v. It lowers volume slightly on my 1987 build, and seems to enhance and smooth upper harmonics in a very pleasing way. I'd say it acts more a PPIMV but holds mid and bass better with much more transparency.
I can't play well enough to tell if it's Eddie's brown sound but it appears to lean toward it. I'm gonna have one of my buds who can play to try to record on Sunday.
Not really mythic at all!

[SilverFox]

Do you have a link to that voltage bucking transformer project? I'd be interested in seeing how that was done for the information value.

silverfox.

[sluckey]

Here's one. See page 2...

http://home.comcast.net/~seluckey/amps/ ... apbook.pdf

[SilverFox]

Thanks, I actually have the old version of your AmpScrapbook and just replaced it with the newer one in my reference library. Information overload- Got so much stuff sometimes don't remember what or where.

Hope and expect retirement is going well. Perhaps a good time to be away from all the weird disruptions with HF vision systems and I don't expect the Rev C. eng fixes will resolve the cause. There must be a fix to it though since the source doesn't fall out of the sky. Hmmm. Thanks again for the Link.

silverfox.

[billyoung]

I used to have to do 3 phase buck boost setups was a pain in butt.

Often used 16 and 32 volt increments. Seen my dad do crazy ones, add 100

to 440 volt to get 550, add 50 to 220 to get 277 for lighting.

[RWood]

I used keen's
http://www.geofex.com/Article_Folders/v ... ntvolt.htm
I used a 40v ss Fender transformer using center tap for 20v.

Thanks R.G.!