Looking for ideas to reduce power used by a tube heater

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Learning to Wiggle
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Looking for ideas to reduce power used by a tube heater

Post by Elahrairah » Fri Jun 26, 2020 11:00 am

I've built a handful of valve modules in eurorack. I like the imperfect behavior using the analog of analog transistors. Specifically it's a 12ax7 but should apply to others, since it's "effectively" got a 33Ohm resistor inside to self-heat when power is applied.

Since it's a dumb heater, I assume I can lower the power used and the only drawback is the heating time, and wont impact the final temperature if the room isn't refrigerated.

My first thought was to reduce voltage with a resistor divider, but that may be just wasting the power elsewhere, it reduced the power usage of the heater element, but doesn't reduce the power usage of the whole module. Similar with an in-series resistor: putting another 33Ohm in series gives the heater half power but I guess wastes the full amount from 12V to 0V? I'm a bit confused, since it seems like putting a 100KOhm between power and ground doesn't get super hot, but in the case of the series heaters both parts are getting hot. Ideally I'd have a trimmer in there to configure heating time vs draw, but I'm worried a dumb trimmer will burn itself up.

I started from here, and it's a mess I'd like to do better before building more modules.
https://www.lookmumnocomputer.com/proje ... orting-vca

When researching ways to reduce power usage, there's a lot of talk of trimming features off your microcontroller, altering clock speeds, or reducing voltage. If I use a 5V line instead of a 12V line... well the 5V line is just a 7805 on the 12V line, so I guess that would have the same or worse overall power consumption!

Ed: I can add the original designs were measured using about 250mA on cold start, declining to 150mA after a minute or two. If I could sit the thing at 50mA constant I could run 5 times as many modules on the same capacity PSU, and I don't mind if they take 5x as long to turn on.
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Learning to Wiggle
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Re: Looking for ideas to reduce power used by a tube heater

Post by bodmin-moor-boy » Fri Jun 26, 2020 11:16 am

Yes, any regulator or other resistive divider will still use power. One way would be to use pulse width modulation (PWM), turn it on a bit, off a bit, the thermal inertia will even it all out. But your thinking is wrong, less energy going in will result in less temperature of the filament and thus less emission. But might work for your application? Cheers bodmin-moor-boy

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Re: Looking for ideas to reduce power used by a tube heater

Post by EATyourGUITAR » Mon Jun 29, 2020 9:14 am

after stasis, your terminal temperature is proportional to your power consumption in watts. reduced voltage is also reduced power therefor reduced temperature. the only way to get the power consumption down without reducing temperature is to use a tube with less mass in the heater and less mass in the tube. a sub-miniature tube is the way. there are also starved plate designs but that is probably not why you like tubes.

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