Interesting power converter - anyone use these?

[mlabbee]

I ran across a dc-dc converter at hosfelt (listing pasted in below). It appears to take a 12 volt/3amp input and converts it to 100 v.  

I've been toying with building a pre-amp or amp with 6021 tubes (like in the nanohead and powerman).  I haven't really sat down to do the calculations yet, but it seems like these tubes will work fine on 100 volts (any thoughts on that number also appreciated).  

Has anyone used one of these d/dc converters?  I can't find the data sheet on line and don't want to order one if it's no use, but it seems like this would be a really easy way of eliminating a transformer and simplifying the power system.

Thoughts appreciated.

+-100V DC/DC Converter   $US9.95      

Mfg. - SPRAGUE
Mfg. # - 200ZDCP88101
2-1/2" x 2" x 7/8"
Input:  12 VDC @ 3 amp
Output:  +100 VDC
               -100 VDC
Ripple and noise output.
500 mV peak to peak max
from 50 Hz to 200 Hz.  
Transient response 500
micro seconds.  Spec sheet
included.

[Gilles C]

The only downside is that it is a switching power supply.

Some people say it's not good in audio. You can hear its switching frequency in the signal.

But Craig Anderton uses one (a switching PS) in his preamp design, so I suppose it can't be that bad...

At that price, you should try it.

Gilles

[mlabbee]

That's what I was thinking - so cheap.  I'm guessing it's no longer made since I can't find it anyplace else and the Sprague website (now a part of Vishay) has nothing on it.

What exactly is a switching supply?  I've heard that comment before about whine, but as far as I can tell, the nanohead uses a switching supply (at least that's what I thought it was - there was a post on it by Vex a while ago).

[Gilles C]

What exactly is a switching supply?  I've heard that comment before about whine, but as far as I can tell, the nanohead uses a switching supply (at least that's what I thought it was - there was a post on it by Vex a while ago).

A switching power supply is a circuit that converts the DC input to a sine or square wave, rectify it with diodes the same way any AC is rectified, and uses voltage multipliers (or a transformer while it was still an AC voltage the step before...)  to produce a higher voltage than what was fed in. It is then filtered and regulated to the voltage needed.

Added: Oh, "switching" means that the DC is switched ON and OFF to produce an alternative voltage

[mlabbee]

OIC - thanks for the explanation!

It seems like you'd be able to filter any noise out, like you do with rectified A/C.  Is there something else going on with switching supplys that induces nosie that can't be filtered out?

[Peter Snowberg]

The thing to do is to find DC/DC converters with oscillation frequencies that are WAY above the audio range. Many of those little converters run around 100KHz which is wonderful.

Zachary's converter is a "boost" style converter which uses an oscillator to feed pulses of high current into an inductor which then creates a magnetic field. When the supply power is removed the magnetic field around the inductor collapses and the result is "inductive kickback". That collapsing field provides a nice boost in voltage at the expense of current and finally a diode and capacitor are used to store the resulting kick-back.

Most DC/DC converters that come in sealed modules use a transformer approach and work very much like a computer power supply.

http://www.powerdesigners.com/InfoWeb/design_center/articles/DC-DC/converter.shtm

Again... the important thing is to use a high frequency so that simple RC low-pass filtering removes the noise, and what noise does make it through is not in a frequency range that you're going to hear or that will rob power from the frequency range you want amplified.

[mlabbee]

Well, I can't get any specs on the darn thing on line, so I guess I'll just blow teh $10 and see what I get.  Hopefully, it will be useable.  Sure would make life easier . . .

Is anyone familiar with the operating specs on the 6021?  From what I can tell from the data sheets I have, it should work fine at 100 volts B+, but everything I've seen on the Powerman and Nanoheads suggests higher voltages (180 to 230).  Am I missing something on the datasheets?

[Ansil]

http://hereford.ampr.org/cgi-bin/tube?tube=6021

[mlabbee]

Ansil - that's the kind of datasheet I've been looking at (I have a full blown data sheet with all the performance curves and other info).  It says max plate voltage 165 volts, class A operation, 100 volts.  I've been working under the assumption that you should run it around 100 volts (running things at the max not usually being good for their longevity), but the comments I've seen on the Powerman and Nanohead suggest much higher voltages.  

Is there a good reason for running these things as hot as possible? More headroom, perhaps?  I guess the my question is really this - I have reams of information telling me how to desing a circuit around a tube once I've decided what voltage to run it at - I haven't been able to find anything that really tells me what voltage you should start with.  Thus, with the 6021, I guess I'm supposed to run between 100 and 165, but why would I pick any particular voltage?