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Discussion Starter #1 (Edited)
I’ve been wanting to try a variac for many years but there is so much internet noise about these things that I was always put off. I finally read enough to feel confident I wouldn’t screw up anything so I took the plunge! I’ve only had the unit for a few hours but here are my initial thoughts.

I’m not trying to be Eddie and I am not on a quest for the brown sound. My first concern was that my vintage amp was designed to run on less than 120v (which I am measuring out of the wall). Turning the variac down to 110 made a very nice change to the top end. The amp has always been a bit strident with an overly percussive transient. At 110, the top end mellows but doesn’t disappear. The harsh transient fades, the amp becomes softer, and there is much less ear fatigue. For this alone I am a happy camper and the variac was worth every penny.

I then went on to try lowering the juice all the way down to 90 volts. I have read that for many guys this is their favourite setting. My amp basically sounds identical but at 90v you can start to hear a real volume drop. It isn’t massive, but it let me pull my master volume up a notch. You get all the sonic benefits of 110 plus you shave a few dbs off the overall volume. I’ll experiment a bit more and see where I ultimately land, but I am betting I stay under 110.

IMPORTANT: Thanks to an online tip, I was warned that the meter/dial on my variac is crappy. The very first thing I did was grab my multimeter and check out the readings. Sure enough, the meter/dial on my variac is consistently about 7db high! I quickly grabbed some tape and marked off different settings on the dial (120, 110, and 90). I am very thankful to have know this because you could potentially fry something if you set the variac for 120.



FWIW, here is the unit I bought: SC-3M | Variac with Meter - 3A, 300 Watt



TG
 

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COOL thread!!

Is the output on a Variac reasonably well regulated (i.e. given that the input in from the AC in homes typically varies to some extent) and/or does it vary in relation to the load?

Looking forward to more of your sonic/tone related comments.
Maybe some comparison clips at different voltages?...Hint, hint.
 

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Great write-up, @traynor_garnet . I appreciate that. You make me want to hop in the car and go and buy one.

I’m not trying to be Eddie and I am not on a quest for the brown sound. My first concern was that my vintage amp was designed to run on less than 120v (which I am measuring out of the wall).
This is, IMO, the best reason to use one. Chasing tone is silly to me, but operating an amp as it was designed to operate is completely logical. A quest worth researching. And you've had some interesting equipment lately in your quest. I'm always glad to hear your opinions on this stuff.

@greco I don't think this unit has extra regulation (by the looks of it). It will just track the incoming voltage of your wall socket at a certain percentage determined by the dial. And you are correct, wall socket voltage varies throughout the day - and more or less depending on where you live and so many other factors. It is very unpredictable.

I think you can buy units that have good internal regulation - or a UPS - but they're a lot more money as well.
 

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The numbering is based on a specified input voltage, and can also just be inaccurate. In your case the spec says 110VAC input, so if the voltage is too hot going in, it will also be high coming out. In your case I'd expect '110' to give 100% of what is going in to the variac.

Another thing to monitor is the heater voltage. I'd expect it to be pretty close to 6.3V when the 'vintage' AC level is applied. But make note of what the heater voltage is at the various settings you use. Somewhere around 5V on the heaters I'd expect you may get drop-outs.
 

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Discussion Starter #5
Measuring for 110v input voltage explains why the meter reading is consistently off; my wall is putting out between 118-121.

I've read about the heater voltage concern before. To be honest, I don't know who to measure it. I never go below 90 volts and I am usually a bit above. I can live with shorter tube life if I am getting the tone I like.

The numbering is based on a specified input voltage, and can also just be inaccurate. In your case the spec says 110VAC input, so if the voltage is too hot going in, it will also be high coming out. In your case I'd expect '110' to give 100% of what is going in to the variac.

Another thing to monitor is the heater voltage. I'd expect it to be pretty close to 6.3V when the 'vintage' AC level is applied. But make note of what the heater voltage is at the various settings you use. Somewhere around 5V on the heaters I'd expect you may get drop-outs.
 

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If you are just lowering the voltage, I'd think you will increase tube life if anything.
You'd have to measure the heater voltage inside, typically across the pilot light in a classic Fender amp.
Excess heater voltage can increase noise and also shorten tube life.
If you are never raising the AC to the amp, I don't see any down-side (except sound drop-out if you go too low).
 
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