take me down to variac city

[chuckocaster]

so here i am, i have 2 variacs now. the first one i got out of a dumpster, my buddy owns a scrap yard and said if i wanted to dig through a bin with electrical stuff in it i could have whatever i wanted.

so here she is, i had to change the fuse and tighten up the brush, but it works now. a powerstat to boost, 7.5 amps.





the second one i need to piece together, i need some connectors and screws, but she's pretty much all there. i think i'll add a switch to the power up the variac. there'll be one set of isolated plugs, the other plugs will be off of the variac. i think i'll also put in an indicator light for when the variac is on. i hope to have this one alive this weekend time permitting. coolest thing is it has an old triad 1/1 transformer!

[phantomman]

Paraphrasing Linc from "The Mod Squad"......

SOLID!

A variac is mandatory for any tech who intends to perform serious amp work on his bench.

Ya done good, kiddo!

[chuckocaster]

thanks roger, i have a couple ideas in mind for amps. one involves making a high power flip top... i asked KAP'N about it a long time ago, and i've still been dreaming of it.

[Cygnus X1]

Good stuff Chucko.
Mine is also a 7.5A Powerstat, courtesy of my father in law.
He used it for his photo studio.

I use it to form up caps and very old equipment.
Never try the "EVH trick" though...not a good idea.

[steve25]

I have that same powerstat model sitting right next to me as I type this.
I have another also from a different maker, but I use this one the most.
Being able to bring the volatge up above line lets me check out how the bias changes with varing line volatges.
A example would be at home I have 118 volts most times, here at work we have near 125.
That will make for a difference you can hear in a fixed bias amp.

[Mesotech]

I also have that powerstat model. As stated, it certainly comes in handy when working on amps.

[elicross]

"But...this one goes to 140."

[cwilliamrose]

I have one that may be much older than my VV. The patent dates back to 1936. Last we tried, it seemed to be in working order. It has been collecting some mojo just sitting around.







It might be a good idea to make a cover for the back. The switch is not original equipment.......Bill

[Offshore Angler]

Now you need a Plexi to run it with! The "brown" sound. Whooohoooo!

[Cygnus X1]

Just MAKE SURE that it is grounded well and correctly.

Variable AC voltages can...and will find the most convenient path.
Meaning when it is below say...100V when the load is expected at 110+, things can get wonky fast.

You don't want it blowing up in your hand (not all that likey), or just routing itself through some other unexpected path.

I have tripped out breakers with variacs.
Not good.

[Cygnus X1]

Now you need a Plexi to run it with! The "brown" sound. Whooohoooo!

Wish I could find it, but it is partially myth (I know you had your tongue in cheek...but hey you never know about some other people).

Eddie had his amps modded to lower the B+, and used the variac to supply a known 115V in venues where GOK was being delivered.
Acts as a stabilizer more than anything.

I have a stabilizing transformer also.
(Not isolation...wish I did).

[chuckocaster]

my main plan with the small one is to regulate the voltages on my old amps 115-117. my house isn't soo bad, 122 out the wall. but there are a couple clubs we play where i've measured it at 127... gee, i wonder why my amp sounds weird?

[chuckocaster]

okay, so i've been working on the behemoth today. i just can't seem to get it to go. wired as per a site i found here http://www.nmr.mgh.harvard.edu/~reese/VariacPage/ that's what came up from a google search. still, no worky. any ideas?

[chuckocaster]

i have feeling that the neutral (white wire) needs to tie into of be connected to terminal 3. i don't know if this is correct or not. could really use some help.

i attempted to wire it up earlier today and fried it, luckily i had another (extra) variac that my buddy gary gave me. still, this one does not want to go with the the diagram i posted. like i said though, i think the neutral needs to tie into the power line. i tried tying in to ground before and was rewarded with an electrical fire.

[Cygnus X1]

Ouch!

[Don]

Chuck! I've also got that same Powerstat 7.5 amp variac, 'cept mine isn't grounded. That's what I was looking for that grounded courtesy outlet for a few months ago.

If anyone knows a source for a grounded outlet, let me know.

[Offshore Angler]

Just MAKE SURE that it is grounded well and correctly.

Variable AC voltages can...and will find the most convenient path.
...

No, they wont.

Voltages don't move.

The less resistance, the lower the voltage.

People routinely get shocks of thousands of volts throughout the day and are no worse for the wear.

The current will divide, not take the path of least resistance. But, it the resistance in a leg of the network becomes zero, the Amps will be limited only by the current supply.

[Cygnus X1]

No, they wont.

Voltages don't move.

The less resistance, the lower the voltage.

People routinely get shocks of thousands of volts throughout the day and are no worse for the wear.

The current will divide, not take the path of least resistance. But, it the resistance in a leg of the network becomes zero, the Amps will be limited only by the current supply.

Willing to take a bet on being the third leg on that theory?
I certainly won't.
My description of theory is weak but, ground can become hot in a bad heart beat, and I will not take that 50/50 chance.

Best to play it safe and make sure those old variacs ARE properly grounded, than debate what might happen otherwise.

[Skip]

Maybe this schematic will help? I have no idea
http://www.mzentertainment.com/pics/...schematics.gif

[chuckocaster]

thanks skip! that's EXACTLY what i needed. i had a feeling that the common leg of the outlet needed to tie into the variac somewhere, i just wasn't sure where. you saved the day dude!

[chuckocaster]

IT'S ALIVE!!!!!!!!!! THANKS SKIP! I'M GONNA BLUE LOU THIS POST.



NOW ALLS I NEED TO DO IS FIGURE OUT THE ISO TRANSFORMER AND WE'RE GOLDEN. THEN IT'LL BE PIMPIN IT OUT WITH A LIT POWER SWITCH, FUSE, AND SOME EXTRANEOUS CRAP TO FILL ALL THESE FREAKING HOLES SOMEONE DRILLED IN THE CASE.

AND I DIDN'T CROP THE PIC SO YOU DUMBASSES CAN SEE THAT MY DESK IS NOWHERE NEAR CLEAN, AND THIS IS THE 3RD DESK, THE OVERFLOW!

[Offshore Angler]

Willing to take a bet on being the third leg on that theory?
...

ABSOLUTELY. How's $100 sound? I'll go easy on you.

Clue: the dielectric strength of air is about 3kV/mm.

[Offshore Angler]

Wow, the schematic they show does not match the picture of the wired up circuit. The schematic does not show a ground to the transformer and the picture is missing the bridge rectifier for the meter, and the shunt resistor for the meter as well. Although I can't for the life of me figure out why they would use a DC meter in an AC application.

[Offshore Angler]

Willing to take a bet on being the third leg on that theory?
I certainly won't.
My description of theory is weak but, ground can become hot in a bad heart beat, and I will not take that 50/50 chance.

Best to play it safe and make sure those old variacs ARE properly grounded, than debate what might happen otherwise.

Also, ground cannot become hot. That's why we ground things.

[chuckocaster]

update:

i wired in a switch on the variac, along with a pilot light and a fuse. everything is working great, turns smooth and tracks well. i took it tonight to church so my buddy chris could use it with his amps. i metered it in to 117 volts and let him have at it. i don't know if it really did or not, but the amps sounded better to my ears. smooth, but not in a browned out way. i think the biggest thing was getting the line voltages down into an acceptable range. i picked 117 because most of my old amps state they take that.

so for now i'm good, but i want to put a digital readout meter on it so i don't have to use my multimeter to read it. oh well, another day i guess.

[limbe]

I am glad to see that you have an isolation transformer as well chuckocaster.
Limbe

[aclempoppi]

Very good info! Dragged out the old Powerstat just to check it out. It's a 220-110V 9amp model, but without ground. It has a duplex output, so a ground scenario should be pretty straight forward. It's always worked well. Thanks, if I had something of value to add to your disscusions I surely would. But you guys seem to have all the bases covered. Art