OT-US wall voltage?

[Toney]

Hi ,
I am trying to organise a power transformer for a Tweed Champ I want to import. We have 240v at the wall here and these babies are really voltage sensitive. I have to order exactly the right one, if it's gonna sound right.
So, can some one please tell me.......
What is the TRUE US wall voltage?
Was it different in the late 50's?

[Jason Stout]

Check this article:

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

[petemoore]

We used to get more 'brown' power [I read 90vac was not uncommon]I understand in the past like 1950's and the voltage was said to drift ...my father built a Dynakit I use these days, in 1959 [my birth year].
 The bias kept drifting up, and I rebiased it a few times and redid the entire bias arrangement....    ....before I read about how to run amps like this on 'modern' wall power [117vac I think ] by dropping the voltage before the power input....DAFT...works good and alll, but would have been much easier had I known this technique before I did all the work to it.
  I haven't measured it in a long long time, and I'm only reading 117vac around here on equipment intended for domestic use, but I've also seen 120vac written too so someone else can state what exactly it is.
  Interesting subject, I would imagine it's monitored closely these days and the supply is stabel and dependable [barring a blackout].

[Paul Marossy]

Here where I live, I have measured up to 125V at the outlets in my house.

[Toney]

Yeah, the 59 Champ's transformer is rated at 110v but I keep reading of people refering to 117v, 120 etc.
I suppose the manufacturers of the replacement trannies take this into account???
So...... all older gear that was made for 110v is possibly running out of spec  :shock:
Got me wondering, we have 240v, I wonder if thats really 240v or a little higher these days ......

[petemoore]

well if your tubes start running hot or glowing orange on that vintage amp...save yourself a whole rebiasing mess by reducing the input voltage...applicatyions may vary I would surmize

[niftydog]

I think you'll find it started out at more like 220 and has already crept up. But it fluctuates quite a bit anyway. A well designed piece of equipment will take this into consideration.

I just checked my work bench, 228VAC according to my fluke meter. 644VAC peak to peak on my CRO. (those figures correlate, by the way) But it's an unfair test, as I beleive my work bench is part of the UPS system, so it's running via that and not directly from the mains.

I have a recollection of it being much closer to 240VAC at home on the other side of town.

[Paul Perry (Frostwave)]

Something often overlooked is that the mains "sine" wave is very different today, compared to 30 years ago. Back then, you could actually put a scope on the AC and see a reasonable sine, but now with all manner of switch mode supplies, the top of the sine is lopped, and the sine is very ragged indeed.
just one more thing to worry about.. plus, Australia is (maybe aready has?) changing from 240 nominal to 230 (like UK) but, this is really a fraud, the voltage isn't necessarily changing at all, the 'allowable error' is going to cover the original voltage, so nothing needs to be done at the power station.
Maybe it is time to get a variac!!

[Boofhead]

I looked into this once but it's little vague at the moment:

The official voltage is 120VAC but it's not uncommon to find it down at 110VAC - obviously there will be extremes outside of this range.  The wide variations are probably due to the large number of different suppliers in the US and the fact they could be distant from users.

Australia is usually pretty close to 240VAC (I believe Perth is generally higher).

[Boofhead]

I wonder if thats really 240v or a little higher these days

The higher voltage means the cables can be thinner (and lighter) for the same amount of power transferred to the user - at least up to the HV transformer.