Anyone run a Variac?

redking

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If you don't want a CHARIAC (or is it "VARIACH" now?) you can find the original US VARIAC branded ones by General Radio company on eBay used for not much more. I've had those, as well. Usually, you'll want to clean them carefully and replace the hookup leads with modern heavy gauge, well insulated wire, and make sure the grounding system makes sense and is up to today's standards.

I do use a Chinese one, myself, but I've removed the core to put it in a larger steel rack chassis with some other power regulation and metering equipment, grounding it well.

If you use a Chinese one, just look around on YouTube to see how to fix the internal chassis grounding. There is high direct-connected mains voltage just millimeters away from the improperly grounded steel chassis, with moving parts inside that move when you put your hand on it. Not good.

The indicated output voltage being inaccurate on the dial and meter is no big deal. If you need an exact reading (because EVH said "89 volts" or something) just put a proper meter after it.
Sounds like a good solution - however I am not an amp tinkerer or builder, so it's easier for me to buy something I know works properly from the start - lol. I'm also thinking the Brown Box might be good for me because I have no need to get it down to 89 or whatever number, I just want to run my amps as they were intended. Friedman has said these are good too, but less "variable" than a Variac - however I don't need that functionality.
 

cooljuk

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Sounds like a good solution - however I am not an amp tinkerer or builder, so it's easier for me to buy something I know works properly from the start - lol. I'm also thinking the Brown Box might be good for me because I have no need to get it down to 89 or whatever number, I just want to run my amps as they were intended. Friedman has said these are good too, but less "variable" than a Variac - however I don't need that functionality.
That one that @NotScott posted seems really nice. I imagine it keeps a steady output, regardless of input voltage, as well, from looking briefly at the design.

FWIW - Many Fender schematics say something like "voltages +/- 10%" and the difference between a modern 125VAC mains and the 117VAC mains that Fender indicated is 6.4% so, technically, you are still definitely running them "as intended" on the voltage. Nothing to worry about, there.
 

NotScott

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That one that @NotScott posted seems really nice. I imagine it keeps a steady output, regardless of input voltage, as well, from looking briefly at the design.

FWIW - Many Fender schematics say something like "voltages +/- 10%" and the difference between a modern 125VAC mains and the 117VAC mains that Fender indicated is 6.4% so, technically, you are still definitely running them "as intended" on the voltage. Nothing to worry about, there.
You are right about the input voltage. However, a 10% upward variance in supply voltage has a much more significant effect on B+ supplies. A lot of those vintage amps were designed around 110VAC inputs and were running B+ supplies in the upper 400s, which is right at the limit for many of the caps and other components used back in the day. For example, if your amp was designed around a 475V B+ from a 110V source, if you run that amp with a 120V source, now your B+ is running 519 V and not many of those old components will last very long at those voltages.

Although +/- 10% is typical standard deviation in analog electronics, the designs from 70 years ago were based on components that were already pushing their design limits and modern power isn't doing any of those devices any favors.
 

AcVox

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I've found a number of uses for my variac style transformer. Like most I was curious about the 'brown sound' effect on my 4 hole Marshalls, and found the reduction in volume to be the most useful quality. It comes with a delicious, subtlety compressed attack similar to that of a Vox AC30 tb, or 5e3 tweed Deluxe pushed really hard. Some will love the 'feel' of the reduced voltage, but others will miss the loss of some faster transients in pick response. (Not a problem for Eddie though, eh?)

A compromise that works well is to combine the variac with an attenuator.
Using a Marshall 'Power Break' alone its possible to reduce volume considerably by just two or three attenuation clicks. This reduces the perceived sound pressure level quite a bit with little to no adverse impact on the depth, detail or feel.

From here it's just a question of reducing voltage from the variac to bring either the volume to ideal venue working levels, or simply to that perfect and glorious overdriven Marshall 'sweet spot', volume be damned cause after all, this is rock n roll..
 

jwalker99

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I have used a Brown Box variac for a few years mainly with 50s and early/ mid 60s amps . It works great and definitely improves the tone by “opening up the space” better than most pedals can ever do. That said, 112 -115 is usually the sweet spot. The Guitar player Johnny Hilliard, who is partially blind, did a good brown box video where he demonstrated that 112-115 was the best range for a Tweed and any lower sounded “too loose” while 120 was “to tight. “
 

mrblooze

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I have biased my Marshalls while on a variac and while off a variac. There is still a difference in tone and feel when you compensate for the supply voltage differences. Amplifiers that run a higher B+ will sound more open, dynamic and brighter than the same amps run with a lower B+, even if bias dissipation is set the same for both. You can compensate for some of those effects by altering the bias but B+ is a big factor in the general character of an amp.
The differences in biasing change where the tubes saturate and start clipping. That's where the distortion comes from, as the signal starts to look more like square waves, which are composed of all the odd harmonics of the frequency. If you injected a pure sine wave with a high enough peak-to-peak voltage on the grid, and looked at the signal on the plate with an oscope, you would see how the output signal changed as you changed the bias to increase or decrease the gain... Pure sine wave when the tube is operating below saturation, and clipping the top of the signal off as you bias the tube into saturation.

Point is, all tubes, even all of a certain type, are different, sometimes slightly, sometimes wildly, in their inter-element values and interactions.

So using a variac, or any method of changing the bias, won't necessarily give you the same clipping on every tube. So if one tube doesn't sound good when using a variac, even one with very precise control, that doesn't mean it won't work well on a different tube.

As I'm sure most folks here know, it's a little more complex than just changing the primary power input voltage. Also, the voltage regulator and current regulator circuits in the power supply have an impact, and they're working to try to keep input variations from affecting tube bias, i.e., working dynamically AGAINST letting the variac change the sound. How effective are they in any one, specific amp, as opposed to how effective is that circuit design in general? That has an effect, too: a better regulator circuit will limit how well a variac works. On modern tube amps, like a Buyer's Infinium, the variac trick would be much less effective than a vintage Plexy, regardless pre-amp tube type.
 

mrblooze

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The differences in biasing change where the tubes saturate and start clipping. That's where the distortion comes from, as the signal starts to look more like square waves, which are composed of all the odd harmonics of the frequency. If you injected a pure sine wave with a high enough peak-to-peak voltage on the grid, and looked at the signal on the plate with an oscope, you would see how the output signal changed as you changed the bias to increase or decrease the gain... Pure sine wave when the tube is operating below saturation, and clipping the top of the signal off as you bias the tube into saturation.

Point is, all tubes, even all of a certain type, are different, sometimes slightly, sometimes wildly, in their inter-element values and interactions.

So using a variac, or any method of changing the bias, won't necessarily give you the same clipping on every tube. So if one tube doesn't sound good when using a variac, even one with very precise control, that doesn't mean it won't work well on a different tube.

As I'm sure most folks here know, it's a little more complex than just changing the primary power input voltage. Also, the voltage regulator and current regulator circuits in the power supply have an impact, and they're working to try to keep input variations from affecting tube bias, i.e., working dynamically AGAINST letting the variac change the sound. How effective are they in any one, specific amp, as opposed to how effective is that circuit design in general? That has an effect, too: a better regulator circuit will limit how well a variac works. On modern tube amps, like a Buyer's Infinium, the variac trick would be much less effective than a vintage Plexy, regardless pre-amp tube type.
Sorry. Bugera Infinium )oh, how I hate autocorrect!)
 

The_Nuge

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Hi guys,

I have a big-ass East-German Variac, bought for this very purpose, but haven't actually tried it on an amp yet....
I was picking up my MK IV Boogie, which has a sort of fixed Variac function, from my amp-tech the other day, and he told me that the tubes don't "like" seing less than 6.3V heater voltage. As youd be decreasing the heater voltage with a Variac, is that something to worry about?

Es
 

NotScott

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Hi guys,

I have a big-ass East-German Variac, bought for this very purpose, but haven't actually tried it on an amp yet....
I was picking up my MK IV Boogie, which has a sort of fixed Variac function, from my amp-tech the other day, and he told me that the tubes don't "like" seing less than 6.3V heater voltage. As youd be decreasing the heater voltage with a Variac, is that something to worry about?

Es
The simple theory goes that preamp tube filament supplies like to be around 6.3V. If you go much lower than that, the element doesn't get hot enough to freely give off electrons so other processes at work tend to wear the tube faster than normal. That is the theory. There is some debate exactly how serious the wear is but again, with all things analog electronics, variances of 10% are normal. I have measured heater voltage in a few of my old Marshalls and had one running at 5.9V for over a year with no noticeable issues. Then again, I was running NOS tubes in that amp and they are much more rugged and durable than current manufacture.
 

no jimmy p

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I use my Variac daily . I live in an apartment bldg that was constructed in the 1920s , and I'd guess it still has most of the original wiring (only 1 or 2 outlets per room ). My voltages vary depending on the time of day . I read an interview with J.D.Simo , and he outlined the whys in favor of using a Variac to help get consistent tone from his vintage amps . My GA8-t as well as my Vibro Champ like 107 - 110 volts , with 108v being the sweet spot for the Gibson ... Noticeable difference in tone between 110v on the Variac and the 117v coming out of the wall .
 

redking

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Well I just ordered the Brown Box, so will report back. I suspect the difference will be more in the "feel" than the sound, and I would be happy if I could get my clean, or edge of breakup tones to feel better. With overdriven / distorted sounds, everything feels just fine as is but wanting to play more in that edge of breakup zone.
 

jojo

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Some older amps don't need them, but my vintage orange amps do. They were not designed to be run at modern US wall voltages and need to be run at around 106-8 volts. I measured my jam room at over 122 volts. I use a variable power transformer to step them down. I don't have an expensive one but I check it with a volt meter. Since my tech had me start doing that I've had zero issues with those amps.
 

redking

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Well I just ordered the Brown Box, so will report back. I suspect the difference will be more in the "feel" than the sound, and I would be happy if I could get my clean, or edge of breakup tones to feel better. With overdriven / distorted sounds, everything feels just fine as is but wanting to play more in that edge of breakup zone.
Well, I have been running the Brown Box for a few weeks now and so far, so good. My wall voltage gets as high as 123 in the evenings so one "click" on the unit gets me down to 117 and as low as 114 when the wall voltage is at 120 at different times of the day. The YBA-1 feels great when played this way - not sure I notice a difference in sound since I am playing mostly through my reactive load and IR's but my rig sure feels good right now and it makes me want to play more often, so that's a win in my books so far. I think once I get back to jamming out loud again I will be able to tell whether there is much of a difference.
 

Riffraff12571

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I've got one. I've used it for working on old amps but haven't used it for running any amps yet. I have a bunch of vintage amps so its something I've been wanting to try but I want to put a box over the terminals first and add a receptacle and banana jacks for my meter.

 

FloridaSam

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I have a few vintage amps including a 1962 Band Master that wants 113v. My outlets put out between 123-126.
I bought an AmpRx Brown Box. One of the best decisions ever. Amps sound better and run MUCH cooler.
 

cooljuk

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I was looking at autoformers that can handle lots of current. Stuff that will put out a constant voltage, regardless of the varying mains voltage. Something to take several amps to whatever voltage I want, and hold them there over time, in a studio environment. I found this. Looks like a massive DC power supply and re-inverter, to me. 11 Amps, at that!

In addition to voltage regulation, I could feed my British amps 50Hz! ....so my hum would have that warmer English sound. :fingersx::hmm:

 

jwinger

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I use an AmpRX EuroVolt with any of my vintage amps. Works wonders and highly recommend it. Amps run cooler and just sound 'right'. I bias with them at the reduce voltage.
 

redking

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I use an AmpRX EuroVolt with any of my vintage amps. Works wonders and highly recommend it. Amps run cooler and just sound 'right'. I bias with them at the reduce voltage.
I assume the Eurovolt is the 220 version of the Brown box? It looks similar.
 

jwinger

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I assume the Eurovolt is the 220 version of the Brown box? It looks similar.
Exactly! And I'm getting 246v out my wall believe it or not! For UK I take it down to about 220v. For US voltage amps I use it after a step down transformer, which may give me 125v out or something and then then I take it down to 110v or so with the eurobox.
 


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