3 Oct
2008
3 Oct
'08
12:21 p.m.
On 3 Oct 2008 at 19:27, Tony Duell wrote:
I am suprised. Over here, most mains transformers have
2 off 115V
primary windings that you connect in series for 230V mains (Europe) and
parallel for 115V mains (USA). I assumed (given that 115V-input
transformers are not commonly needed over here) that such things were
available worldwide.
Well, if split-primary transformers were common here, the problem
would be solved wouldn't it? Use one of the primaries as a 120v
secondary and the low-voltage secondary as normal. I used to have a
cache of surplus filament transformers that I'd use to power small
tube/valve projects in that manner.
But all wall-wart supplies that I've seen here (which is about the
only easy way to obtain small power transformers) have a single
120vac primary. It might be that the cost of the extra copper
required for 220vac operation justifies a separate product run for
North America and Japan. (Somewhat OT is that Japanese mains power is
spec-ed somewhere around 100vac. Expats who brought their US-rated
appliances (such as a refrigerator) were often disappointed by the
short motor life when run on Japanese power).
Totally OT, but if you're trying to run one of
those valved portable
radios that used a 90V HT supply, it's worth noting that a 30V
transformer (the ends of a 15-0-15 winding, for example), voltage
doubled, gives about 84V. That's run all the radios I've tried, including
an AM/FM (yes, a valved FM portable radio) Vidor set.
Given that many battery-powered sets used a 45vdc "B" battery, I
would agree with you.
Cheers,
Chuck