LED displays (TIL305, TIL308, etc.)

[Chuck Guzis]

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