The Variac: Variable Voltage Transformers & Tube Amps - Explained

Today in Plague Scythe Studios, I demystify an iconic guitar player's use of a variable voltage transformer in his rig, and how they affect your tube amplifier!

[PlagueScytheStudios]

Some interesting information from Ceriatone's Nik Azam regarding the results of this video:

"Some of the older amps have very high voltage. Some Super Leads were close to 500V B+. The preamps could also have higher voltages, whereas in lots of these hot rods, the voltages are lowered already, as part of the voicing.
I think the preamp voltages have a lot to do with it. The Jose types are already 90-130V, whereas most Marshalls are higher. Definitely hard to capture, as opposed to have a vintage Plexi cranked up, and then using a variac.

I think we have done one before, exactly like the Boogie, by having a power transformer with extra taps. So it was either 490V B+ as stock, or 360V (for about 75% from the wall). With the stock Super Lead circuit, the difference was very notable, definitely.

I think it's also a function of the time - back then in the 70s, there were not that many pedals like now, and people had to come up with this sort of thing. Even basic things to us now, were magical stuff back then."

[pointymason]

You have somehow managed to combine the both of my worlds, electrical engineering and guitar playing into one! Love your videos, keep them coming!

[monsterk]

Ryan, your playing is always great, but, bro. You were on FIRE in this video. That Megadeth section was phenomenal. Love your videos man. Stay safe brotha.

[fuzzybrain]

Ah! Finally the Variac explanation I have been looking for. Thanks for this.

[BrandonBames]

Your production is looking and sounding much improved lately, good work man! The extra work is definitely showing!

[deadviny]

A Variac can also help do some very incipient, simple troubleshooting

[bikesnbeerz]

So far, 0 people thought they pressed the download button. Uncommon in other videos.

Good job.

[JimmyDevere]

To me the Variac sounded better than the tweed setting. I wonder if the extra transformer is effecting the sound? As another has commented, I have read contradictory things regarding tube life and vairac. Since mesa is not using an actual variac I don't know if there are technical differences in their circuit, and some people say a variac can prematurely damage an amp. What do you think?

[vox]

Nice video try with greenbacks I use the vintage modern cabs with the Hendrix speakers with plexi head and variac at 90 volts with cascade mod on preamp tone is awesome

[FedericoMK]

great video, as always, keep the tech videos coming!
btw I like what you're doing with the mark IV GEQ (750 hz down and 2200 hz high, 6600hz small bump if any) :)

[lucasbentes]

My AC30 2010 seems to stop completely or cut the sound after while depending on where I’m playing specially if the electrical facilities are not the best. The variac would do the trick to keep the amp stable?

[hambone]

Is there away to attenuate voltage to power tubes but not to the preamp tubes?

[RubyRoks]

This is fascinating! I've been simulating this by running a tube compressor VST on the in and out of my amp sims and it gets that chewyness, but it doesn't give it the right sound

[duckydrummer]

Not knowing anything about electronics, transformers, etc. I didn't understand a word of what he was saying, BUT "Pissed Off Plexi" We should coin that phrase because that exactly describes Eddie Van Halen's sound on that first album.

[EvelynRoods]

I see an orange dark terror living on the top of that amp shelf....

How about input attenuation ... IE the 1 watt switch

[mariannwatt]

I was thinking about getting a brown box for my 68 50w marshall plxi . its bone stock and has no mods and all the guts transformers etc are intact and if i used said brown box i would have to have it rebias to 110 v my wall voltage is 123v isnt that right? this amp never goes out of my studio and ive never had a problem with it at 123v my tech looks it over every year what do you think ?

[mikeyseward]

I figured you would be the one to ask as you are kinda the "Mesa Guy" (at least to me) on YouTube, I was wondering if you are familiar with the Strategy series of power amps and how I could use one in the fx loop of an amplifier to give it more headroom, I'm currently running a Randall RH1503 solid state head and want to use the 400 watt iteration of the Strategy, what effects in tone could that help or harm? I want to keep the Solid state damping but as with a lot of solid state heads more watts seems to be accepted as more better

[emmettgros]

Im a Peavey amp user I've used the XXX for years with the built in loose-mid-tight switch which honestly depending on your style of playing or style of music was very beneficial, playing rock set to tight playing death metal set to loose, now I'm playing on the Invective and it only has 2 setting full and half power full power sounds so much fuller with 6l6's. One thing you didn't even mention that different power tubes 6l6, El34, el84, kt88 all react differently to a variac and different levels of quality of tubes react differently to a variac there are literally thousands of combinations

[sildz]

What voltage does mesa boogie amps use?. Is the amp switcheable worldwide?. The country where i'm at right now operates on 220V!. Do i need a transformers in case i'd buy one in the future?..thank you!