Tubes on 12v? What tranny?

[Gnome]

Ive seen a couple of preamptube based preamps and a head which is driven on 12v DC. I just wonder what kind of trafo that's used.

It's about the Z.Vex NanoHead and the Mesa V-1, both has 12v input. The nanohead even produces enough power do drive 4x12 cabs. So any info of any kind will help!

Thanks in advance!

[cd]

Search for "Real McTube".  In general a 12V>240V (or higher) transformer is used to bump up the 12V to high plate voltages.  In the case of the Nano Head, an inductor based switching power supply is used to bump the voltage up.

[Gnome]

Thanks, saw it, looks like a cool projeck, however. Any ideas on where to find the tranny? I then need something that get 12v up to 140-300v somewhere.

[cd]

Read the article again.  You use a regular 240V>12V or 120V>12V transformer wired backwards.

[Paul Marossy]

You can get around 140V with the back-to-back xfmr configuration such as in the the Real McTube circuit. You have to use a pair of 500mA minimum transformers to get that voltage. If you want 300V, you're going to have to use a different transformer to accomplish that, something like those Hammond transformers that AntiqueElectronics sells.

[cd]

You can get 300V easily by using a 240V>12V transformer.  Most of the new 12V>120V transformers I see have series/parallel wiring for worldwide operation, so you can wire it as 12v>120v or 12v>240v, 24V>120V, etc.

[Paul Marossy]

Ah, right... that could work. It seems to be just as simple to get a transformer with a couple of different secondaries, though.  

[Hal]

how do these circuits convert the DC to AC to be transformed - is it a simple astable multivibrator - square wave output, or do they use some other, better "power inverter" circuit?

The only schematic i found that was discussed is the real mctube, and that uses mains voltage.  http://www.dogstar.dantimax.dk/tubestuf/mchowit.htm

[Paul Marossy]

The McTube doesn't convert DC to AC. It uses two AC transformers and two full wave rectifiers - one supply is for the 12.6VDC tube heater and the other is approx. 140VDC for the plate of the preamp tube.

[Gnome]

Thanks, you have enlightened me!

I will try to build a powersupply like the one in the Real McTube someday.

[Gnome]

But, is there any possibility to take 12v DC and get it up to 240? I know I can do it with AC. I'm just curious. How do they do this in the Z.Vex Nanohead.

I'm a total noob on this, but I'm trying to learn enough to one day make my own Tube Dist Pedall, from my own spec.

[Paul Marossy]

As cd said, you can use (1) 120VAC/12VAC and (1) 240VAC/12VAC transformer to accomplish that. You would connect them like this:

120VAC-->12VAC--/tube heaters/--12VAC<--1204VAC

So, you would have 120VAC going into the first transformer with 12VAC coming out of the secondary. The second transformer's "primary" would be the 12VAC side, with ~240VAC coming out the "secondary". Get it?  

To get DC on either the 12VAC or 240VAC leg, a full wave rectifier is used. Look at the Real McTube schematic, and you will see how it's done. I didn't get it at first, but it's a very clever way to do it with just a couple of cheap wall warts that can be disected, as the creator of the Real McTube circuit suggests.