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I'm in the process of creating a tube guitar amplifier with an output power of ~6w (fender vibrochamp AA764) which requires the use of 360-400vdc. How could I obtain such a voltage from mains without using a transformer? I thought about using a full bridge doubler, but that rises the issue of noise and chassis space occupied by large capacitors.

EDIT: The guitar is connects directly to the grid of the first preamp tube via a pair of grid stopper resistors, the ground of the amplifier and input jack being common with that of the 3 prong power cord. Here's a schematic of the original, although I would completely omit the standard power supply section and the so-called "death cap" before the primary of the power transformer. I would also add an insulation transformer before the whole thing.

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    \$\begingroup\$ Please edit your question to explain how you are going to provide isolation between the live audio circuit and your guitar. \$\endgroup\$ – Transistor May 14 at 18:27
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    \$\begingroup\$ Are there specific reasons you can't, or don't want to, use a transformer here? \$\endgroup\$ – duskwuff May 14 at 20:58
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The guitar is connects directly to the grid of the first preamp tube via a pair of grid stopper resistors, the ground of the amplifier and input jack being common with that of the 3 prong power cord.

That's OK provided that your power supply is isolated. The first part of your question says, "How could I obtain such a voltage from mains without using a transformer?" so you have conflicting statements in your question.

Here's a schematic of the original, ... I would also add an insulation transformer before the whole thing.

I presume you mean an "isolating" transformer. Again this conflicts with the opening paragraph of your question.

You can get 360 V DC by rectifying 240 V AC and using a smoothing capacitor. That's what the 5Y3GT rectifying valve is doing. This could be replaced by a bridge rectifier. You still require the isolating transformer.

The alternative is to use some form of switched mode power supple (SMPS) which will convert the mains to HV DC. The advantage - if a suitable SMPS can be found - is that of weight.

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  • \$\begingroup\$ Rectifying and smoothing 240V will only get you 336V. \$\endgroup\$ – Fleetie May 15 at 13:23
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A switching regulator (Boost topology) or a voltage doubler + linear regulator. Solutions with transformers will generally give better performance than those without though.

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  • \$\begingroup\$ The issue i have is that I can't find any SMPS designs at these kinds of voltages. It's mostly low voltage high current applications rather than reversely. \$\endgroup\$ – Calin Ionut May 14 at 20:07
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    \$\begingroup\$ The design doesn't change dramatically, you just have to make sure that the components are properly rated. \$\endgroup\$ – Oscillonoscope May 14 at 20:33

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