12VDC to 150VDC Converter

[nashvillebill]

Okay, it's winter and I'm spending too much time thinking up crazy ideas. So as I was going through my tube stash, my eye kept coming back to some of the last-generation miniature tubes. like the 5719. Then I thought about an imported bass sitting here that I converted from active back to passive, so it has lots of available room in the control cavity....and I started thinking:

Put two of the 5719's with their heaters (6 volts) in series (total 12V, using 150 mA for the heaters) inside the bass. Make an external 12 volt power supply, good for about 500 mA or so. Use it to supply power via the third wire in a regular 1/4" shielded TRS cable...the other two wires would be ground of course and signal. So the bass would use a traditional 1/4" TRS jack just like it would have with a regular 9V battery-powered preamp.

It gets crazier...now also use the 12V DC to power a 12 VDC to 150 VDC converter onboard the bass. I'd only need about 10 or 15mA total to supply the two plates of the 5719's. And there we have it...an onboard tube preamp, running a pair of triodes at 150 Volts. (I'm assuming the 150 VDC that's produced is clean enough to use as B+, I have no experience with them).

I just need a 12 to 150 VDC converter that's a) small and b) cheap....only need 15mA output. I checked Mouser, they had a 5 watt version but it was close to $40 each. Any ideas? Again, I have no experience with modern day DC to DC conversion. (I do have a few dozen vibrators from 1950's car radios around, but they wouldn't exactly work in a bass...)

Of course, I could just put the 9V battery back in and whip up an op-amp preamp for a couple of dollars in parts, but what's the fun in that?

[R.G.]

It gets crazier...now also use the 12V DC to power a 12 VDC to 150 VDC converter onboard the bass. I'd only need about 10 or 15mA total to supply the two plates of the 5719's. ...
I just need a 12 to 150 VDC converter that's a) small and b) cheap....only need 15mA output. I checked Mouser, they had a 5 watt version but it was close to $40 each.

150V * 0.015A = 2.25W
5W isn't all that out of line. It's a little generous, but not terribly. And $40 is pretty cheap compared to finding or winding your own magnetics.

The bigger issue with an onboard high frequency converter may well be switching noise. Some converters are LOUD in the RF.

Conversion efficiency on a switcher can be in the 80-85% range easily, 90 requires competent work, and 98% is getting near magic. So this thing needs maybe 2.25W/0.85 = 2.65W in at 12V. That's 220ma by itself. If you run the filaments in series and they pull 150ma, then you're needing 370ma of 12. OK, a 0.5A 12V supply would work.

[Chuck H]

And let's not forget how the onboard fan will mess with the pickups Or is the cavity with the tubes in it NOT going to be cooled? This doesn't even account for some anomalous failure putting 150V in your hands just waiting to find a ground.

[eschertron]

And let's not forget how the onboard fan will mess with the pickups Or is the cavity with the tubes in it NOT going to be cooled? This doesn't even account for some anomalous failure putting 150V in your hands just waiting to find a ground.

Bill mentioned it would be 'crazy'... I think 'exciting' goes without saying.

[J M Fahey]

It would be worth pursuing if tubes worked better than transistors, but since they do not ....

[es345]

I just need a 12 to 150 VDC converter that's a) small and b) cheap....only need 15mA output.

This might fit (shop in Germany)TT VPump - Spannungskonverter - Tube-Town GmbH

[Mick Bailey]

I've done this plenty of times using a simple SMPS, though my target has been 250v from a 12v supply - enough to power a couple of 12AX7s. My inductors are just a few dozen turns over a 3/4" long piece of 3/8" ferrite rod taken from a transistor radio. You can buy commercial ones for very little anyhow.

Take a look at Nixie power supplies - here's an excellent circuit that I can verify works. The switching transistor needs a very low on resistance - the lower the better. The IRF740 gets pretty warm with full-size tubes, but I manage to run them with a DIY copper flag heatsink. The inductor isn't critical, but is the key to efficiency. Plenty of room for experiment and it will build into a small space. You may need to screen it, but I've never had problems with switching noise due to the high frequency.

http://www.turbokeu.com/myprojects/n...ixie%20psu.gif

[trobbins]

Perhaps some ebay options for about $10 delivered - the 75W option is very compact and I can't really fault it :
http://dalmura.com.au/projects/75W%20car%20inverter.pdf
http://dalmura.com.au/projects/Car%2...0converter.pdf

[nashvillebill]

Thanks trobbins but those are too big. Here's the Mouser one by comparison--just a through-hole DIP24 R12-100B RECOM Power | Mouser 31.8 mm by 20.3 mm x 9.4 mm

I thought of making a ventilated cavity control cover. Or making it out of aluminum and mechanically anchoring the back of that Mouser chip to the aluminum as a heat sink. Tubes could go in the (now empty) battery compartment, again with a ventilated cover...

[eschertron]

It would be worth pursuing if tubes worked better than transistors, but since they do not ....

Make sure the tubes are visible through a transparent cover, and the exercise will be worth the 'wow' factor!

[R.G.]

Make sure the tubes are visible through a transparent cover, and the exercise will be worth the 'wow' factor!

Even there, I'd use a carbide drill bit and drill through the glass button on the bottom of the tubes and insert an orange LED.

[tedmich]

Even there, I'd use a carbide drill bit and drill through the glass button on the bottom of the tubes and insert an orange LED.

if you work fast you might not even have to glue the LED; vacuum tubes suck!

[eschertron]

Even there, I'd use a carbide drill bit and drill through the glass button on the bottom of the tubes and insert an orange LED.

That's such a DIY thing to do. The mainstream manufacturers simply put the bright LED behind the tube. From a distance, through beer goggles, it'll still look pretty cool!

[g1]

I'm waiting for a tube with a little ship inside the bottle. Maybe led's for port & starboard lights.