Voltage and Impedance Switches

[martin manning]

What shall I do with that specific position? Should I ground it and maybe add a black tape on top of the 200V writing?

Don’t ground it, that would likely be a direct short across the mains! Just leave it unconnected and that position will result in nothing happening as no voltage will be applied. What power transformer are you using? Got a link to its data sheet?

[Bombacaototal]

What shall I do with that specific position? Should I ground it and maybe add a black tape on top of the 200V writing?

Don’t ground it, that would likely be a direct short across the mains! Just leave it unconnected and that position will result in nothing happening as no voltage will be applied. What power transformer are you using? Got a link to its data sheet?

Thanks for the reply Martin. Got it! I appreciate the help! So the unused position will wrl somewhat like a standby

This is the PT
http://www.classictone.net/40-18097.html

And the data sheet is here
http://www.classictone.net/40-18097.pdf

[martin manning]

An unused position would be like a main power off. However, that single-pole switch will not work with the transformer you linked, since it requires a parallel connection of the dual primaries for 100 and 120V, and series connection for 220-240V.

[Bombacaototal]

Ah yes!! How did I miss that

Thanks for the help Martin! I guess I only have the following options:

Switching between 120V/240V (or 100V/220V) done with a slide, toggle or rotary switch.

Switching between 220V/230V/240V with a rotary switch.

I have to think which will be more useful...as I am in the UK now and need 230V probably the latter, and at least I have Europe covered

[Reeltarded]

You might have better luck finding a step transformer that does at least most of the voltages you think you might use. Japan is harder to find unless you are in Japan... I think in that case you might want to shop for a switch in Japan if you are still set on having everything on an installed switch... or just buy a second step down made for their service. I bet you could find used ones cheap.

[Bombacaototal]

Just one unrelated question. Is a 2Amp fuse enough for a 50W amp? And 3Amp for a 100W?

[pompeiisneaks]

That depends on the amp. You'd need to calculate the operating range of the amp, and give it a little buffer etc. How many tubes in use, how much heater current used etc. There's also a basic ratio, as you up voltage in a transformer, you lower the current it can carry. (as voltage goes up, current goes down, and conversely as voltage goes down, current goes up. See here for an explanation:
https://www.allaboutcircuits.com/textbo ... nsformers/)

If you look at each winding (heaters 6.3V at say 5A, and reverse that back to the PT side depending on the turns ratio, you'd see a lower amperage at the primary side) and convert the current to the expected on the other side of the winding ratio, you can see what to expect for the current at the 120V side. Then I think you generally give it a bit of breathing room, but not too much. I.e. say you added up 2.3 amps, the use 2.5 or 3 amps. Someone may know more precisely exactly how far above to go, but you don't want tubes to start runnign too hot, pulling way more current than expected and not blow out the fuse.

The B+ side often has one as well, but that's a bit easier to calculate, because you can look up the exact current you'll draw per tube and any other devices on the power rail, and set it to be a bit over that amount. Usually those are like 250mA or something smaller.

Hope that makes sense. If you were to specify the exact amp you're asking about, then someone smarter than me probably will know the answer off the top of their head.

~Phil