110? 115? 120? When did US wall voltage change, and from what to what?

SerpentRuss

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Everyone realizes that that 120 volts (240 volts) is transformed very close to where you live, right? If you live in a suburban setting you probably share a transformer with a couple of neighbors, more in an apartment building. If you live in a rural setting you might have your own transformer. Many of these transformers have reduction and boost taps.
 

David Barnett

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Everyone realizes that that 120 volts (240 volts) is transformed very close to where you live, right? If you live in a suburban setting you probably share a transformer with a couple of neighbors, more in an apartment building. If you live in a rural setting you might have your own transformer. Many of these transformers have reduction and boost taps.

I'm always amazed by the wispy little spider web of a wire that goes from the primary of the transformer to the HT line.
 

RodeoTex

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I've been an electrician since 1977 and have seen the voltage creep up from about 122 to 129 in that time. Sometimes 131.
My best guess is that to deliver the same KW, it is easier to raise the voltage rather than increase all the wire sizes to accommodate increased loads.
 

chas.wahl

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Here in NYC, with a big, monopolistic, dirty-energy utility (ConEdison) 120/208 service is very common, especially in "pre-war" residential buildings (even very large ones) like mine -- built in 1928. Our 1100 SF originally had two 20 A (15? there were always 20 A fuses in there) circuits, all wired with cloth-covered rubber insulated 14 gauge. That would have been at, let's say 110 to 115 V. A previous owner added a third circuit obviously (renovated kitchen), and may have had some change done to the power supply (though whatever it might have been was done through the original conduit preceding the panel). I heard something about a general building power supply update happening before we owned, but in the 2010s there was a major capital upgrade, giving us (whooeee!) 80A service (yes, 120/208) and a bigger panel. That's not really enough for a planned renovation with electrical heat (greener, if the grid greens) rather than steam radiators. Our voltage is pretty stable at 121–122 V or so and doesn't vary much from the farthest circuit/outlet to the panel. I'd like to rewire with 12 gauge, but need a crafty electrician to do that, as much as possible, through existing (steel tubing) conduit, if possible, and minimal disruption to wood floors (over concrete slab and cinder fill) that aren't being replaced wholesale.
 

David Barnett

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Here in NYC, with a big, monopolistic, dirty-energy utility (ConEdison) 120/208 service is very common, especially in "pre-war" residential buildings (even very large ones) like mine -- built in 1928. Our 1100 SF originally had two 20 A (15? there were always 20 A fuses in there) circuits, all wired with cloth-covered rubber insulated 14 gauge. That would have been at, let's say 110 to 115 V. A previous owner added a third circuit obviously (renovated kitchen), and may have had some change done to the power supply (though whatever it might have been was done through the original conduit preceding the panel). I heard something about a general building power supply update happening before we owned, but in the 2010s there was a major capital upgrade, giving us (whooeee!) 80A service (yes, 120/208) and a bigger panel. That's not really enough for a planned renovation with electrical heat (greener, if the grid greens) rather than steam radiators. Our voltage is pretty stable at 121–122 V or so and doesn't vary much from the farthest circuit/outlet to the panel. I'd like to rewire with 12 gauge, but need a crafty electrician to do that, as much as possible, through existing (steel tubing) conduit, if possible, and minimal disruption to wood floors (over concrete slab and cinder fill) that aren't being replaced wholesale.

Don't forget Greenwich Village still had DC power until surprisingly recently.
 

GPoint

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For a tube amp is to check and compare input AC voltage and heater voltage inside the amp - they are proportional.
The optimal heather voltage is 6.3v AC.
Using an AC Ferro-Resonant Stabilizer (to get stable AC voltage after it), and the following Variable Autotransformer (Variac) you can adjust the amp's powering to this optimal heater voltage.
Then adjust Variac on any other AC voltage you subjectively like for your tone and remember this AC voltage for this amp!
P.S.
- Too high heater's voltage is reducing tubes life.
- Too high plate voltage in some cases can damage power tubes (depending on tube specifications), but in most cases just increases the amp's output power.
- Concerning power tube BIAS voltage - it is following proportional to Plate voltage, it will be more or less adequate in most cases.
 

HotRodJon

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Fascinating comments. Especially appreciate the NYC-relevant comments - spent all my youth in the 60s and 70s growing up there. Lots of studios on the wild west side of Manhattan that I hung around.

Agreed that the actual voltage you'll see at the end of your branch circuit receptacle may be reduced quite a bit from what the utility would like you to see. Good to keep an eye on it since sagging voltage (especially in the summer, when lots of AC units are pulling a lot of "real" power from the grid and also pushing "reactive" power back onto the grid) will increase the input current drawn by an amp.

For products designed to work on "110V", it may be an issue, such as for antique radios. Not so sure it matters as much for an amplifier but I'd need to think about that a bit more. But in any case, if you want to to be safe, you don't need an expensive Variac (that is, variable autotransformer), since you only need a half dozen volts to match the actual line voltage at your receptacle to the nameplate rating on the amp. A simply 6.3V filament transformer can be wired as a 6.3V line voltage reducing autotransformer. I built one to use wth my 1942 Philco AM radio, to knock down the nominal 121Vac I usually see at my receptacle to something closer to the original 110Vac rating of the radio; in this case, about 114Vac, which is good enough for me.
 

padreraven

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This is a lot to learn. Growing up in the 50s and 60s we all learned that wall outlets were 110 and stoves or dryers with big three-prong wall outlets 220. Of course that was when if you blew a fuse you really blew a fuse, and you had to go to the hardware store to the big box of fuses and find the matching one. There weren't breaker switches. The plugs on appliances didn't have one big and one small prong, they were the same size; and if you wanted a grounded 110 extension cord you bought one that had two prongs and a wire with a hook on the end that you had to put on the screw in the wall socket. Three-prong outlets were rare. But I never heard of the different voltage ratings, and I don't remember when suddenly they were all 120 and 240 instead. Once again it turns out that I didn't know as much as I thought I did.
 

King Fan

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Back at the DIY Ranch, if we think 1950s amps were running on 115 or so (in many places), and if we own a vintage amp **or** a clone running a spec PT, building a simple bucking transformer makes sense. How? I linked above to Rob's 5E3 mods page which includes among more complex models a simple single-voltage ~112-115 version. From this discussion and my experience, the single-voltage version would be simpler to build and adequate for most uses. If you have a 1930s radio, or an amp (not rare) that runs *way* too high on B+, the -7/-12% version, low voltage around 107-110, might be handy.

Here's the original R.G. Keen article.

http://www.geofex.com/article_folders/vintvolt/vintvolt.htm

Here's a great build with some useful comments:

https://www.tdpri.com/threads/my-take-on-robrob’s-“buckminister”-bucking-transformer.938477/

And FWIW my build, where I figured out a few practical details that woulda been obvious to smart people, and better yet, got helpful advice from smart people…

https://www.tdpri.com/threads/brown-box-vintage-voltage-adapter-build.1035420/

Oh, and I finally got around to some clear labels.

CFA57FA4-F34A-4CF7-B139-1E6E0BA9EDA6.jpeg
 
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chas.wahl

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My notion about this is to have the duplex outlet, pilot light and fuse -- or maybe not even the pilot light. One outlet is -6.3V, the other -12.3, and if you want normal wall voltage, you unplug the thing and plug your amp into the wall. Yes, there's no "hot swap." But no switches, and I realize that's not an approach that @robrob's might endorse wholeheartedly, but I think it works OK.
 
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King Fan

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My notion about this is to have the duplex outlet, pilot light and fuse -- or maybe not even the pilot light. One outlet is -6.3V, the other -12.3, and if you want normal wall voltage, you unplug the thing and plug your amp into the wall. Yes, there's no "hot swap." But no switches, and I realize that's not an approach that @robrob's might endorse wholeheartedly, but I think it works OK.
Yes, and IIRC Rob covers several options from basic on up. I like the pilot light but it’s not necessary. Power switch? not really needed, just unplug the box from the wall, but… I don’t need to do that. Normal outlet? I ended up with one power strip on the low outlet and another on the wall outlet for lamps, my PR, my pedalboard, so the normal outlet is seldom used — just gives me a place to quickly plug in the voltage meter if I’m curious about wall voltage, which is seldom. Final deluxe frill for me is the -12% setting — unless you have really ancient gear or really massive B+ overshoot, it's kind of the point of this thread that maybe 112-115 is '50s vintage correct. But it’s handy and fun for comparison — and instant bias change. And I built it this way partly for the fun of it.
 

chas.wahl

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OK, since we've swerved in this direction, let's discuss bucking transformer percentage drop on a 120 V primary. Do I infer correctly (didn't see it stated as a principle in @robrob's Buckminister material) that the larger the VA rating of the transformer you use, the larger the % drop?

@robrob says that when he used a Hammond 166N6 rated 25.2 VA, with an input voltage 121.5, he got reductions to 116.9 (4.6 V drop) and 112.9 (8.6 V drop); and when he used Hammond 166N12B rated 48 VA, with input voltage 120.0, he got reductions to 112 (8 V drop) and 106 (14 V).

I had (simple-mindedly) thought that you'd get a drop of whatever the voltage ratings were for half and full secondary winding (i.e. 6.3 V and 12.6 V) which seemed to be about right (121 V to either 114.7-ish or 108.4-ish).

I have a Triad VPS12-6300 rated 80 VA (!) I guess that means I'd end up with reductions that are even larger, maybe too large to be useful. It looks like the actual current loading through the transformer is a factor as well as the actual primary voltage. Maybe I should look for something with a lower rating, like a Hammond 166L12 rated 31.5 VA.

Another thing that occurs to me: @robrob says he started out with a Hammond 166N6, which, so far as I can tell, is a 117>6.3 V transformer (25.2 VA) with a center tap (presumably 3.15 V per side). Well, how does that work? There's another Hammond transformer, the 166L12B that is a 12.6 V center-tapped model with the same 25.2 VA rating. Does the secondary voltage spec of the transformer not make that much difference, compared to the unit's VA rating?

And another: Hammond's specs for their 166 series has primaries varying -- 115 or 117 V. What is that about? The VA for all of them seems to be based on the secondary voltage times the Amp rating, regardless of the primary voltage listed.

Finally: Is there a reliable way to calculate this? Using nominal voltage found at the wall, approximate power consumed by the amplifiers one wants to use a bucking box with, and any other factors (such as the secondary voltage spec)?
 
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King Fan

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Another thing that occurs to me: @robrob says he started out with a Hammond 166N6, which, so far as I can tell, is a 117>6.3 V transformer (25.2 VA) with a center tap (presumably 3.15 V per side). Well, how does that work?

Rob says the 6.3V transformer only dropped voltage ~3.5%, so he went to the 12v to get more like 7%. I’m no EE but I figure it's a “bucking” transformer in the sense of bucking the tide, voltage-wise.
 

Wharfcreek

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As an 'old guy' who's been around since the early '50s, I figure I'll drop a comment or two here just for further consideration. My Grandfather worked for the City of Grand Rapids, Michigan, and he was the Superintendent of Power and Water from the time my mother was a little girl of 8 or 10 to when I was a teen-ager. The power station was literally outside his house, which was actually a residence belonging to the City, but given to him as he had 24/7/365 responsibility for this stuff. The Transformers were massive, and the high-voltage contained inside the fenced in area was such that at night, stuff would 'glow' in there! You'd see these small 'arcs' of electricity along with this almost 'alien' looking purple hue to the color. Anyway, according to gramps, the supply of electricity would vary significantly, which would cause some pretty significant fluctuations in voltage levels being transmitted out the power lines, which in turn would enter the transformers on the lines in the city and neighborhoods. A lot of this was just the simple result of 'supply and demand'. So, 'average' levels were quoted, but no guarantees were ever offered by anyone anywhere!!!

Taking that back to the commercial production aspect of things, one has to consider that any manufacturer basically had to put 'something' on their product! You had to distinguish it as being either a 'US' wall voltage device, or something else, like European, Asian, Canadian, etc. So, while the engineers were perhaps busy quoting line-voltage specs to each other during the creation of this stuff, a lot of those 'labels' were generated well after the whole engineering and production process was completed. And, those labels were there to satisfy Uniform Commercial Codes (UCC) as a function of retail legislation as much as anything else. They simply told the consumer: This is for a USA wall plug..... or not! So, I think looking at those labels as being some kind of true electronic spec, like one would a Schematic....... I don't think those labels were ever intended for that!! Further, my understanding on Fender as related to the 'specs' you see on the schematics you find for their products is that many, if not most of the early ones, NEVER had specs associated with them in the first place. It was mostly done as 'fill-in' by techs in service departments who wanted numbers, took measurements, filled in the open spaces on Fender's drawings, and then this stuff ended up becoming published in books, copied on Xerox machines, and finally ending up on the internet as gospel. Not so, according to my understanding!!

Anyway, I think the point of this is: What's 'safe' for an old amp as related to today's wall voltages? And, I think there's a post somewhere ahead of this one where someone indicated their concern was more the 7+ volts on the filaments of the tubes than the fluctuation in HV or B+ levels. In today's world, where a damn 12AX7 is now, what, $25 +/-? I think that's a legit concern! As to; How will the amp sound based on voltge fluctuations? Well, that's another subject entirely! And, just to finish up my comments here, I'd say that amps are like guitars: Play 20 of the same Telecaster 'new' off the music store wall, and of the 20, 2 or 3 will be 'great', 2 or 3 will be 'not good!!', and the remaining group will be just 'OK'. My point being that virtually every amp out there has it's own individual character. Yes, you can alter that by changing the voltage going to it, but people change tubes, speakers, transformers, capacitors, resistors, and even modify their cabinets just to achieve a sound they like. So, if you want to worry about something related to voltage, worry about how long your tubes will last before the lights go out inside of them. Otherwise, the 'tone' is all a variable you probably are already tweaking around in some way or another......

That it from me!!
 

LunarSF

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The AmpRX Brownie, if you have old amps, is one fun option to consider. I had a '62 Princeton and I was getting 123-125 in my house at the time. Plugged that in and was able to dial up really different responses from the amp. You can even get it down into the 90's. I don't have a need for it anymore but still kept it because it was such a cool tool.
 

chas.wahl

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Rob says the 6.3V transformer only dropped voltage ~3.5%, so he went to the 12v to get more like 7%. I’m no EE but I figure it's a “bucking” transformer in the sense of bucking the tide, voltage-wise.
It seems to me that it was connected up exactly the same way as the 12.6 V "bucker" was, with a choice of half the secondary winding or the full thing. What was the transformer that you have used? The 166N12B? I don't really want that much "drop" in the two steps. I'd like to drop 4-5 V for the first step, and 9-10 for the second.

My speculation here was that the VA rating matters more than the secondary voltage spec, but if @robrob used transformers of two different voltages, that conclusion is problematic. I guess I have to get the Triad 80 VA transformer out and rig it up to test the output when it's connected to wall voltage; and then load it by connecting to an amp and see what happens.
 




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