This should have its entire own project on HackaDay, and maybe soon it will.

Usually a tube amp needs a high voltage transformer, I decided to attempt something different here since early on I was unsure about the final voltage I would want, as well as wanting dedicated 15V rails for op-amps and other lower voltage circuits.

I started development of a solid state power-supply in 2018. Early on I tried a cheap eBay high voltage module, after destroying two at a very low load I decided to move forward and make my own.

Some of the requirements that developed over time:

• 24V input voltage so I do not need to deal with 120V AC line isolation.
• Variable output voltage: 250-360V, 28W
• Heater Voltage: 6.3V, 3A (With Softstart)
• Negative Bias voltage: -30V
• Op-Amp rail voltages: ±15V

Below is the first revision of the board, it only had a high voltage flyback and a buck converter for the heater. It lacked the 15v regulation and negative bias outputs that I would later want. The layout was not great and I had stability issues due as well.

For these kinds of requirements, the only option was to wind a custom transformer with multiple windings. Winding a flyback transformer, and air gaping it with Kapton. Later transformers used parallel primary windings to reduce the skin effect losses, as well as multiple auxiliary windings for the negative bias and op-amp voltages.

Lots of engineering, math, testing and measurements later... I eventually ended up with this:

A roughly 60W power supply 88% efficient under nearly full load. meeting all the requirements above. Looking back I would now design the supply to run off of 120V instead of 24V. I would also move to a GaN switching FET. But this works...