• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

DC/DC converter to power tube amp?

needtubes

Member
2003-05-24 9:23 pm
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?

Thanks
 

EC8010

diyAudio Moderator Emeritus
2003-01-18 7:57 am
Near London. UK
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...
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
> 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).