120v circuit 220v adaptation

[helix]

Hey everyone! I'm building a very simple tube overdrive, power supply section of the schematic can be seen above. I will be dealing with 220v instead of 120v, and my question is:

to get 210v B+ what kind of values would I need to change as far as components are concerned (apart from the transformers)? like in the rectifier portion, and the other components in the power supply section? It'd be great if I could get a 120v transformer for the second one, but I can't just buy one, I will have to get it custom wound.

sorry for the nooby question but I'm still learning

thanks!

[AdamM]

I assume you're talking about the second transformer, which steps the voltage back up?

Something like this would get close: http://uk.farnell.com/pro-power/ctfc12-12/transformer-12va-2-x-12v/dp/1780844 - you would connect the two 115V windings in parallel for the secondary, and the two 12V windings in parallel for the primary.

But the circuit is using a voltage doubler (the two 1N4007's and 10u caps). If you use a transformer with a single ~220V winding, and replace the doubler with a straightforward rectifier + smoothing capacitor it would work fine. For the transformer linked above, you'd connect the 115V windings in series, giving ~230V - close enough for rock & roll.

[helix]

Well, my mains voltage is 220v, hence available transformers are all 220volts. I could order a 120v one but it'd cost me. I do have two 12v-220v transformers at my disposal and I'd like to work with them.

So as far as I can understand: (I'm still learning so bear with me)
the diodes and the capacitors are the voltage doubler portion.
the secondary of the second transformer gets doubled to get B+.
since my transformer will already have a 220v sec. I will just need a rectifier and a smoothing cap.

if it's not too much to ask, can you direct me to a suitable rectifier schematic? (full/half wave? full bridge?) and I'm assuming I will have to calculate the smoothing cap value accordingly.

[PRR]

[antonis]

100nF ceramic across each diode is strongly recomended..

On lethal side, just after fuses, a MOV should be a good idea..

And maybe a 100R resistor in series with 100nF parallel to the lamp..

Fusing is - as always - complicated but bear in mind that you have to undersize the 110V recomended value to about half...

[PRR]

Correction to my plan: fuse goes AFTER the DPST switch. (So an idiot can change the fuse without un-plugging.)

Until this becomes your Main Rig, I would not fool with POVs or diode-caps (unless my religion told me to).

That said: the microwave oven we had for 30 years was never the same after a nearby (50 feet!) lightning strike. Symptoms suggested a full-wave rectifier had turned half-wave. Caps and more POV might have averted this. But there is some difference between a long-running household appliance connected 24/7, and a music amp used a few evenings a week. And even in hindsight, if GE had offered a $5 cap+POV option for extra robustness, I'm not sure I wudda taken it.

[davent]

Correction to my plan: fuse goes AFTER the DPST switch. (So an idiot can change the fuse without un-plugging.)

Or use an integrated IEC/Fuse socket, the power cord must be removed in order to get at the fuse.



Why not a 220v/12.6v wall wart to power the backwards second transformer, keeps the mains voltage outside the box.

dave

[PRR]

> keeps the mains voltage outside the box.

+1!!

Someone with "nooby questions" probably should NOT be working with wall power. Aside from electrocution, you can burn the house down.