Converting 9V to 300V (ish)

[fryingpan]

So, there is a line of pedals by Sushi Box that purportedly take 9V as a power supply and power the tube circuit at a high voltage (300V? Whatever is required for the employed tube, which should be a 12AU7 - EDIT: the manufacturer states about 320V).

My question: are there any step-up converters that actually do this? Otherwise, I'm assuming they are using 9V to power an oscillator, buffer such oscillator so that it can output, say, 300mA (parallel devices? Class B output?) and then use a step-up transformer to then rectify the signal and get something like, dunno, a 10mA supply at a high voltage?

Otherwise you can use a boost converter but won't that present huge ripple?

[FiveseveN]

Nathan uses switching converters like everybody. See https://www.diystompboxes.com/smfforum/index.php?topic=93936.0 or look for "Nixie power supply".

[fryingpan]

Nathan uses switching converters like everybody. See https://www.diystompboxes.com/smfforum/index.php?topic=93936.0 or look for "Nixie power supply".

I didn't know there actually were such converters. I was familiar with more moderate step ups.

[drdn0]

The 555 wiggler is cheap, quiet and very easy to build. Doesn't require any fancy parts (although likes low-ESR caps), and pretty much foolproof. Here's one I built last week.

B+ is 280v

I wouldn't waste my time/money on any other setup unless you need a LOT more current (these are good for 12ma or so without too much heat). If you needed way more, use one of the cheap Royer inverter boards and just modify it for some extra filtering (and you can pull 20w out of them easily on the HV side).

[PRR]

Whatever is required for the employed tube, which should be a 12AU7 - EDIT: the manufacturer states about 320V).

That's a show-off rating. The 12AU7 is often run with 100V supply, and does OK below 24V for small-signal audio.

And don't you want 'toan', 'flavor', 'distortion'? Less supply voltage is more signal stress.

[R.G.]

I didn't know there actually were such converters. I was familiar with more moderate step ups.

As a general rule, you can convert any voltage to any other voltage, given that you have switching devices that can work that low or high, and that you are willing to pay the energy losses to any inefficiency. Car ignitions regularly convert 12Vdc to as much as 20kV, and did so even with only mechanical relay contacts. ("points")
A flyback (boost) converter can pretty easily make a few hundred volts. It's done regularly from as little as 3Vdc for radiation detectors ("Geiger counters"). Boosts of ~100x are not too hard, but may need special care in the step-up inductor/transformer.

[fryingpan]

Honestly, the idea of having even 100V in a pedal makes me feel uneasy. It may only be capable of a few tens of mA but we're talking about a device that is going to be abused (literally stomped on). That kind of voltage would warrant double insulation at the very least.

[merlinb]

You worry too much, loads of consumer gear does this, and plenty of pedals run off wall voltage too.
There are some good threads on boost converters for tubes:
https://www.diystompboxes.com/smfforum/index.php?topic=74088.0
https://www.diystompboxes.com/smfforum/index.php?topic=130852.0

[duck_arse]

You worry too much, loads of consumer gear does this, and plenty of pedals run off wall voltage too.
There are some good threads on boost converters for tubes:
https://www.diystompboxes.com/smfforum/index.php?topic=74088.0
https://www.diystompboxes.com/smfforum/index.php?topic=130852.0

https://www.diystompboxes.com/smfforum/index.php?topic=110915.msg1019214#msg1019214

just today I was running a valve at 90V with this circuit.

[fryingpan]

You worry too much, loads of consumer gear does this, and plenty of pedals run off wall voltage too.
There are some good threads on boost converters for tubes:
https://www.diystompboxes.com/smfforum/index.php?topic=74088.0
https://www.diystompboxes.com/smfforum/index.php?topic=130852.0

And old CRTs internally upped the voltage to, what was it, 3kV? And a microwave oven does something similar. Still...

[drdn0]

Honestly, the idea of having even 100V in a pedal makes me feel uneasy. It may only be capable of a few tens of mA but we're talking about a device that is going to be abused (literally stomped on). That kind of voltage would warrant double insulation at the very least.

All the tubes are entirely internal. Sockets are mounted perpendicular to the rest of the PCB. There is almost no way you could damage it to the point where HV is shorted out to the case, and even if so it's going to kill your power supply rather than you.

[Jim Hagerman]

For anyone building a custom boost converter to power tubes using an LM555, I've come up with an easy way to reduce duty cycle ("on" time) below 50%. I employ this trick in all my converters, as it allows me to let things settle better or reduce overall frequency. Normally, we are stuck with a given "on" time where the inductor field is charged up (volt-seconds), but maximum current needs to be limited. This resistor trick allows you to fix on time while adjusting off time and frequency. Up to a point...

https://hagtech.com/pdf/LM555-Duty.pdf

[PRR]

>  I've come up with an easy way to reduce duty cycle ("on" time) below 50%.

I think many such tricks have been lost as designers move on and databooks crumble.

Defrock this feline: https://www.edn.com/add-one-resistor-to-give-bipolar-lm555-oscillator-a-5050-duty-cycle/


https://www.edn.com/design-low-duty-cycle-timer-circuits/
simple addition of a bypass diode makes this timer circuit valid for low duty cycles.



Wikipedia: https://en.wikipedia.org/wiki/555_timer_IC#Shorter_duty_cycle

Just in a few minutes I found references to ideas from "as long ago" as 2006. But we know Hans sold his prototype in 1972 in-part on a super-comprehensive applications guide (which is now scarce).

Walt Jung's IC Timer Cookbook is 1977 and can be found today as PDF or on paper https://www.abebooks.com/book-search/title/timer-cookbook/author/walter-jung/  Sadly it does not cover small duty factor or mention Hans.