12V to 250V schematic? (Tube in pedal platform)

[mirage_indigo]

Hiya gang,
Does anyone have a favorite 12V to high voltage (250vish) schematic anyplace? I can build a small self contained preamp power supply from wall voltage, but I'm trying to get something compatible with my DC7 at 12V, .5A.

I'm waiting for my spot to come up in the Kingsley Pedal lottery, but figured I'd mess around with a couple ideas for a stand alone preamp to put in front of a new HX Stomp (heresy! modelers! I know).

I'm planning out a dual envelope preamp, something along the lines of the KoC design in Tonnes of Tone, but in an effort to make it pedalboard friendly, was looking at powering it off of a 12V .5A rail from the pedal powers supply.
I'm assuming also that running some kind of isolation for the filaments might be a good idea? I'm looking at running a pair of 12A_7s, so I could theoretically just string the heaters across the 12V in parallel, but this seems wrong somehow, but I couldn't explain why.

[martin manning]

Look here: https://ampgarage.com/forum/viewtopic.p ... 16#p421716 Common boost converter circuit, which you can power with 12VDC.

[SoulFetish]

You’re not giving yourself much headroom with a limit of 500mA for your 12V supply. That pretty limits you to only using 12AX7s. 300mA of that is already allocated to the 2 heaters. So, if you are really optimistic and hope to get around %90 efficiency, that only leaves you with an availability of 8nA or so For your 4 triodes.

[Pacosipulami]

You’re not giving yourself much headroom with a limit of 500mA for your 12V supply. That pretty limits you to only using 12AX7s. 300mA of that is already allocated to the 2 heaters. So, if you are really optimistic and hope to get around %90 efficiency, that only leaves you with an availability of 8nA or so For your 4 triodes.

heaters directly on 12V take 150mA per tube (dual triode), Booster circuit takes roughly 120-150mA in a dual tube configuration with roughly 2mA current @ HT voltage 250V

The PSU in the link above is also known as the Nixie PSU (Boost Converter) - but the circuit above works at 32kHz, for a higher switching frequency, replace C24 from 2.2nF to 1nF (roughly 70kHz)

[SoulFetish]

Right. Two 12A_7s are going to demand 300mA of the supply. That’s not leaving you much flexibility or room for error. Switching supplies are inexpensive, even for good ones. Why not use a 12V/1A supply? That way you have more options for tubes, and more likely that the supply might survive a short term overload down stream.
Also, you might need to add some inrush current limiting on the heaters when powering on from a cold start. Most switching supplies have short circuit protection, and the cold resistance of the filaments can appear as a dead short in the load, and the can go into a protect mode.

[Andy Le Blanc]

Back to back 12v/120v transformers. A 12v ac wall wort (120v to 12v) externally with sufficient ma. 12v to 120v internally with a voltage doubler.
From DC you could run a chopper. Old school, just like an old car radio, step up to the required B+.