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

[duaneo]

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.

Basically, the 6.3v and 12.6v transformers are wired as a autotransformers (AT). Take a look at the Wikipedia page on autotransformers for details and formulas. I installed an AT in my '63 vox ac15 that was eating el84's, lowered the HT and it is much better now.

You are correct in that both the voltage and va of the AT will effect it's output, but if you are within +/-5v of your target line voltage you shouild be good. Looking at robrob's web page, selecting a 48va transformer is enough to power a 5e3. If you want to apply this to a higher wattage amp you will need a trans with a higher va. But I see no downside to usnig an AT that is rated higher that you need, you may get a slightly higher voltage (less sag), just like selecting any power trans.

 

[chas.wahl]

Hmm -- are the Hammond 166 models really autotransformers with only a single winding? Their construction "looks" like there are two bobbins separated in the middle, and their schematic is the usual graphic of two windings separated by a core. I'm not that knowledgeable in this area obviously.

 

[King Fan]

What was the transformer that you have used? The 166N12B?

Yep. Having said that I seldom use the -12% setting (which runs maybe ~107V where my household is at ~122) I can see a possible upside of smaller steps. But is the effect of say 3.5% gonna be all that useful? Picture you have a (not atypical) level of 6.7V on your heaters; the 3.5% drop gets you to ~6.5. Now if you wanna get granular, maybe you could arrange a 5% and 10% drop. But wall voltage goes up and down a few volts a day at my house; my 112-115 bucked volts are plenty close enough for government work -- and B+/bias/tone results...

 

[chas.wahl]

This is why I am thinking of the Hammond 166L12: 31.5 VA rather than 25.2 or 48. Goldilocks-style -- something that will realize two arguably useful drops. I realize that managing HT, rectifier and heater voltages with one device may not end up at a happy medium that optimizes them all.

 

[ETMusic777]

I bought an Amp Maniac and am dialing in the vintage Fender amps between 115-117 volts. The Amp Maniac is very reliable, well built and I use it as a variac too when bringing recapped amps up to power slowly. It also shows the Amps drawn too.

 

[King Fan]

This is why I am thinking of the Hammond 166L12B: 31.5 VA rather than 25.2 or 48. Goldilocks-style -- something that will realize two arguably useful drops. I realize that managing HT, rectifier and heater voltages with one device may not end up at a happy medium that optimizes them all.

I’m not that hip to VA thinking, but FWIW here’s what Mr. Keen says about picking a transformer in the original article:

“… look at your amp's power rating plate, usually on the back of the chassis. This will tell you the full-power amperes that the amp is expected to draw. Find a low voltage transformer that is rated for at least that many amperes and a voltage that is the difference between the nominal AC power voltage in your town and the rated voltage on your amp, or at least close.

For example, if your wall sockets put out 125VAC, and your amp is rated at 115VAC, 3 Amperes, pick a 10VAC, 3Ampere transformer (8VAC 3Amperes would probably get you close enough, and is common). Wire this transformer up so that the AC line connects to the primary, and the secondary is connected with one end to the end of the primary that is attached to the "hot" side of the AC line. The output of the thing is taken from the "cold" side of the AC line and the free end of the secondary. The secondary adds to or subtracts from the existing AC line voltage depending on which way round the secondary is connected to the primary.”

 

[duaneo]

Hmm -- are the Hammond 166 models really autotransformers with only a single winding? Their construction "looks" like there are two bobbins separated in the middle, and their schematic is the usual graphic of two windings separated by a core. I'm not that knowledgeable in this area obviously.

When the primary and secondary are wired in series it will behave like an autotransformer. I took a closer look at robrob's page, here is the schematic.

166N12B has a 117v primary and a 12v secondary.
You can see that the primary is wired in series, out of phase with the secondary, like an auto transformer only with one section out of phase. You could think of it like a humbucking pickup where one coil has has 117v worth of winds on it and the other has 12v. so you have to look at the winds ratio.

12 / 117 = .1025 ratio
If I put 125v on the 117v primary I would get
125v x .1025 = 12.8v
Because it is bucking (out of phase) you subtract
125v - 12.8 = 112.2v

You would expect that there would be some gains / losses in the transformer, but because the current draw, primary and secondary resistances are not know you can't calculate these gains / losses. You could fully expect that an output of 110 volts would be correct, and this is close enough for guitar amp work.

You could also wire this transformer in phase, apply the line voltage to the top and pick off one of the taps below to get a reduction, like a typical autotransformer.

 

[chas.wahl]

^^^This is all calculation with respect to winds and voltage, but not the VA rating of the transformer used. You said above that both voltage and VA rating would affect the output. By contrast, the autotransformer article's calculations:

Shows that (going from the first equation to the last) the voltages and currents of the input and output are inversely related: I1/I2 = V2/V1 -- which can be expressed as I1*V1 = I2*V2. But still evades me what effect using a transformer with one VA rating vs another transformer, with a different VA rating (other things being equal), will have on the change in voltage drop.

 

[King Fan]

^^^This is all calculation with respect to winds and voltage, but not the VA rating of the transformer used. You said above that both voltage and VA rating would affect the output. By contrast, the autotransformer article's calculations:
View attachment 997522
Shows that (going from the first equation to the last) that the voltages and currents of the input and output are inversely related: I1/I2 = V2/V1 -- which can be expressed as I1*V1 = I2*V2. But still evades me what effect using a transformer with one VA rating vs another transformer, with a different VA rating (other things being equal), will have on the change in voltage drop.

I'm no pro, obviously, but I tend to think of VA when I want to know how much *current* a transformer can supply at a given voltage. Here (following Keen) I take it we want to choose a voltage and just make sure it can supply the max current our amp can draw. So by my simple-minded approach (and Keen's advice) if we had 120VAC at the wall, and wanted 115 and 110 bucked volts on a 2A-max amp, we'd get a 10V transformer capable of providing 2A and wire it up out of phase as above to give a 5V or 10V drop.

 

[Bob Womack]

I grew up and went to college in the South. My father gave me a volt/ohm meter and full tool set when I was fairly young and I ended up serving as my bands' technical director. I checked grounds and wall voltages where we played as part of my safety schtick. When I went to college in 1975 I was hired by the school as an electrician (unlicensed) and did a bunch of electrical work for the college where I worked. The main dorm building was built in 1927 and a lot of the fixtures were wearing out and needed to be replaced. When a student complained of a non-functional outlet, light, or switch, the first thing you checked was presence of wall voltage.

Both my home city and the college were on TVA (Tennessee Valley Authority) power, first under the Knoxville Utilities Board and then under the Electric Power Board of Chattanooga. Both were above-ground supply regions. The typical readings I got through the '70s were 110-112v. We also spoke of 110/220v as the standard power supply. Now, mind you, that could speak more of the state of the distribution net than the supplied voltage.

Bob

 

[chas.wahl]

Here (following Keen) I take it we want to choose a voltage and just make sure it can supply the max current our amp can draw.

Which suggests to me that maybe there's no harm (or unintended consequence) in using a transformer with higher VA than you need, if that characteristic is preventing overheating or other problem caused by overloading it -- and that the voltage drop the device provides might be pretty much the same whether the bucking transformer is connected to an amp with at 1 amp (5F2-A) or a 4 amp (Bassman) fuse, so long as that's within the bucking transformer's rating envelope. Maybe I should be looking at a 8 V CT transformer (Hammond 166N8), for nominal drop of 4 V or 8 V, instead of the 12 or 12.6 V CT models. That would give me more like 117 V or 113 V.

But wait, thinking back to @robrob's article, and reminding myself that the voltage ratings of the Hammond models are 115 or 117, and my own house voltage is 4–6 V higher, maybe I should just use what he did in the first place (with similar supply voltage), the Hammond 166N6, producing reductions of 4.35 and 8.35 V -- right on target.

 

[duaneo]

But wait, thinking back to @robrob's article, and reminding myself that the voltage ratings of the Hammond models are 115 or 117, and my own house voltage is 4–6 V higher, maybe I should just use what he did in the first place (with similar supply voltage), the Hammond 166N6, producing reductions of 4.35 and 8.35 V -- right on target.

The transformer will not care about a few volts difference, if you have a 110v primary and you apply 125v all it will do is rase the secondary voltages. VA is just watts (volts x amps), as long as you stay within its rating you are good. I'd say build it and find out what it does.

 

[chas.wahl]

Thank you! Principle being that one may expect a bucking transformer, like any other, to have higher secondary voltage(s) when a higher primary voltage is supplied.

Now back to the discussion of the when, where, why of 110 - 112 - 115 - 117 - 120 - 125 V power!

 

[dang]

I bought an Amp Maniac and am dialing in the vintage Fender amps between 115-117 volts. The Amp Maniac is very reliable, well built and I use it as a variac too when bringing recapped amps up to power slowly. It also shows the Amps drawn too.

I've used Amp Maniac for over 10 years.
Great tool.

 

[Stratocast]

We see a lot of smart discussions about the idea that in the US 1950s ('tweed') wall voltages were like 110VAC, and 1960s ('BF') voltages were maybe 115, and of course today we 'expect' 120 (and often get slightly more).

But when I go hunting for actual data on the internet, I mostly find received wisdom or at least facts without references (almost everyone agrees Edison started with 110). The best timeline I could find (though still without citations) was this from the wiki on "Mains Electricity:"

"Nominal voltages gradually crept upward to 112 V and 115 V, or even 117 V.[citation needed] After World War II the standard voltage in the U.S. became 117 V, but many areas lagged behind even into the 1960s.[citation needed] In 1967 the nominal voltage rose to 120 V, but conversion of appliances was slow.[citation needed]"

This would suggest that the supply voltage throughout the 1950s easily *could* be (in who knows, NYC? or heh, Fullerton?) 117V. One source of confusion seems to be that "appliances" of all sorts (toasters, light bulbs, amps) were *rated* for different voltages over time. It sounds like maybe, after the supplied voltage would increase, the officially-specified *rated voltage* would (later?) go up, and then that voltage would be printed on the label, year after year, regardless of further changes until manufacturers 'caught up.' Do some 1950s/60s amps say "110VAC?" Does that mean the standards bureaus just hadn't caught up, or amp manufacturers hadn't?

I am totally lost in this thread. What is everyone talking about. ? I was born in 1955 and ever since I was old enough to plug something into the wall socket. I have just plugged it in. Flipped a switch and the item works. Is this NOT how it is everywhere outside of th US. ?

 

[Stratocast]

It’s so funny. People make such a big deal about the voltages with tube amps, but it’s really not that important, with the exception of the Van Halen example. A bias adjustment resolves the Van Halen issue, but it’s a good case in point. Tube technology is resilient. In A blind test most people couldn’t pick out an amp running at 112 or 122. They MIGHT hear a difference, but different isn’t an improvement. If you are one of the few who can, pony up and dial in EXACTLY what you need:

PCR1000MA - KIKUSUI ELECTRONICS CORP.

Compact, switching AC power supply (PWM inverter method) AC output: 0V to 155V / 0V to 310V at 40Hz to 500Hz DC output: ±0V to 219V / ±0V to 438V Peak currents three times the rated current supported (RMS value) LAN and USB standard digital inerface (GPIB factory option) Sensing function

global.kikusui.co.jp

I will add this: I saw Eric Gales at a festival in a small town in Wisconsin and he went through 3 amps. They just stopped working. Next amp, 5 minutes, stopped working. I went up to see if I could help and every amp had blown mains fuses. The small town had poor voltage regulation. THAT is when voltage matters. Enter the PCR1000. The rest of it is people looking for something to do. You think Leo wasted time matching tubes? Slam them in and get the amp out the door. Matching caps? Please! Out of balance adds synergy, anyway 10% tolerances - good enough. The rest of it was trying to meet UL regulations. Go buy a Brown Box if you got to and hit the woodshed. Better use of your time.

I have only blown 1 3 amp fuse in 50 years of playing

 

[King Fan]

I am totally lost in this thread. What is everyone talking about. ? I was born in 1955 and ever since I was old enough to plug something into the wall socket. I have just plugged it in. Flipped a switch and the item works. Is this NOT how it is everywhere outside of th US. ?

These are not the droids posts you are looking for....

 

[robrob]

It's the voltage of the transformer that increases the bucking voltage drop. I tried a 6.3v and it didn't do enough so I went with a 12v 4a transformer (must have a center tap) and it was perfect.

 

[robrob]

The 6.3v transformer dropped wall voltage by 3.7 and 7%. That sounds very close to what you want.

My wall voltage is almost always 124 or 125v so the 12% drop position of the 12v bucking transformer is usable.

 

[robrob]

This is a simpler version that you may want to build: