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DC/DC converter to power tube amp?
DC/DC converter to power tube amp?
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Old 23rd June 2005, 06:54 PM   #1
needtubes is offline needtubes  United States
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Default DC/DC converter to power tube amp?

I found this DC/DC converter (may need to scroll down some) and was wondering if it would adequately drive a tube headphone amp. It states that it will take 12V, 3A input and produce +/-100V at what I guess would be 150-180mA or so.

It looks interesting, if its specs are decent enough for audio. Using this could make a decent portable tube amp, which could be powered by a wallwart at home or cigarette jack in the car. What do you all think?

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Old 23rd June 2005, 08:29 PM   #2
EC8010 is offline EC8010  United Kingdom
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At $10 it's not to be sniffed at. The key point will be whether the outputs are floating or whether they are centre-tapped to the 0V of the incoming 12V. Yes, it's noisy and will need further filtering, but it's worth a go. If the outputs are floating, you might be able to stack two convertors one on top of the other and power push-pull EL34...
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
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Old 24th June 2005, 02:35 AM   #3
PRR is offline PRR  United States
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> adequately drive a tube headphone amp.

Let's see. 36 Watts in, say 30 watts out, 200V and maybe 150mA, you have two ears, 75mA per ear. 200V and 75mA is 15 Watts DC, a simple transformer-coupled power pentode will exceed 33% efficiency, 5 Watts per ear. 5,000 milliWatts at ~90dB SPL/mW is 126dB SPL.

Yes, you should be able to build an ear-buster.

Transformer winding will approximate 200V/75mA= 2K7 impedance. If you can find 2K5, 6L6 will throw 5 Watts through it; if youc can only find 5K, you may only get 3 Watts. At $10, if the output is floating, buy four and get two channels at 12W(SEP)-20W(P-P)... this will match most in-dash car stereos on loudspeakers.

Without a transformer: you will only get 70mA-140mA peak load current. In 300Ω this is killer-loud; in 32Ω it is loud but not ear-crushing. 70mA peak in 32Ω is 2.4V peak, 4.8Vp-p, louder than a 2-AA-power WalkMan or a Cmoy. Not bad. Tube plate resistance needs to be around 1K: 6L6 will come close, some of the TV V-sweep tubes may come closer, 6080 will work though I never thought it was a very good tube. If the +/-200V is center-tapped to the power source, you will have to juggle to get things centered and still get signal in without power-rail garbage.

> if its specs are decent enough for audio.

The spec is dubious: surely this thing does not run at 50Hz-200Hz! Whatever. Drop about 10% in a resistor and then hang some monster caps on it. 10V/0.15A= 50Ω 5 Watts. 100V/0.15A= 600Ω load impedance, much-much-less than that at 20Hz suggests 100uFd 150V. Build up to two stages on that: if it buzzes or you need more than two stages of voltage gain, add a decoupling network for the input stage(s).

> If the outputs are floating, you might be able to stack two convertors one on top of the other and power push-pull EL34...

Using full-floating (500V isolation) "5V:+/-17V" fed with 6V battery, I stacked to 82V to power a beach-radio tube headphone amp. Or at least I got as far as testing the power system... never got to the amp. But the technique works within the converter's isoation rating. (Costs $10 to find that out: I can't find full specs for this part posted anywhere).
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