Tube power from +/-16vdc

[Denyle]

What's the best method to power tubes from a lunchbox power supply. The heaters seem like they would be tricky as they draw so much current. I'm beginning a nuvistor tube preamp and I'm wondering if it's worth the effort to stick it in a lunchbox. I was thinking I could float the ground and use a voltage doubler circuit for the HT. Any thoughts or insights?

[ajwells]

The heater current will be what kills you on this. If I remember correctly, a 12AX7 pulls just at 1/2 amp heater current. If there are multiple tubes, you can series the heaters, depending on their voltage, of course, or use both rails for 32 volts with several heaters in series. Also be aware that some tubes use the heater as the cathode, and putting a tube like that in series with other tubes will seriously whack out your circuit. To be even close to current specs per module, you would probably want to make a 2 slot module. As far as B+ supply goes, there are any number of dc/dc converters out there, depending on the plate voltage you need. Again, current will be a factor. Best wishes on this.

[Denyle]

Yeah, I've seen some high voltage (300v+) dc-dc converters, mainly marketed for lasers or photo flash bulbs. I wonder how efficient they are though.

[peterc]

I have been looking at a 500 series toob project, & my most likely candidate will be the 6418. Only has a gain of 8, but can be cascaded.

http://secure.oatleyelectronics.com//product_info.php?products_id=722&osCsid=f7b834300989b3f55c05416c1db52f44

Peter

[ajwells]

Depending on whether or not you're intent on using full sized tubes, there are any number of low voltage tubes out there, most of them made in the late days of tube manufacturing. I can't remember any specifically offhand, but they were made for car audio, most have a plate voltage of 12 volts, they were trying to get around the weird circuitry that was necessary to get high voltage from 12 volts.

As far as dc/dc converters go, a lot of them will have high frequency hash because of the way they work. This could be tamed by a small bypass cap to ground to remove the high frequency component. The rest of it should be ok, again depending on the plate current.

The 6418 is indeed an interesting looking tube. There was some concern on a couple of forums about life expectancy, but this may have more to do with the filament voltage not being regulated than actual life expectancy of the rest of the thing. The spec on the filament is 1.2 volts +/- .25 volt. These were military tubes, and you can pretty well expect that the military would not use tubes that would crap out after a couple of hundred hours. Googling 6418 will bring up a Tung Sol spec sheet on these. Filament current is rated at 10 milliamps, which would definitely fit within the VPR specs.

We actually have several projects underway using the 6418, should be interesting to see how it all turns out.

[pan60]

glad to see you here ajwells!
thanks for the input: )~
pan

[ajwells]

Hey, thanks

I'll be nosing around here as time permits.

See us then.