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Author Topic: Tecky Q SMPSU  (Read 2570 times)

phatt

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Tecky Q SMPSU
« on: April 08, 2011, 11:12:01 PM »
Hi All,
        A recent posting about the *SC Valve Preamp Kit* got the brain thinking again.

I am trying to establish if this power supply from the silicon chip Valve preamp kit
can run a small pp power stage.

I have built one of these kits and it works great.
The schematic and pictures of the SMPSU can be viewed here;

http://diyaudioprojects.com/Tubes/12AX7_Preamp/

As I'm not up to speed on this technoligy I'm at a loss as to how to establish just how much current can be safely extracted.

My understanding is that it may well be able to deliver a lot more current as these switcher transformers are highly efficient.
one only has to look inside a computer to see that the ferrite tranies are small yet deliver massive current.

The plan is to use 2 6GW8's (ECL86) and one AX7 with the whole thing running from a 17VDC plug pak (wallwart)

So the heater demand @ 12VDC will be around 820mA, which can be supplied via a seperate supply if need be.

The current draw from the wallwart in the unit I built is around 230mA, which of course runs the heater of the AX7 at 12 volts after regulation as well as the HT supply.

So I measured the heater which draws 140mA which tells me the switching circuit is using 90mA to run VHT for 2 triodes.
As triodes only draw a couple of mA then it's a big leap to run two pentodes which need 140mA.

The original artical did hint that the SMPS could run a lot more Valves but gave no estimate of it's actual potential. Darn. :grr

I did find a nixie tube SMode circuit which is tiny and yet can deliver 25mA @ 170VDC. Got me thinking again.

Any help in this regard would be great.
If it's all to scary I can then set my mind at rest as I do have a normal transformer which will give me 320VDC for HT but I'm trying to make this super compact and the SC Valve supply might just be the trick.

I know switching supplies are voodoo to some audio folk but I'd still like to try it out. 
Thanks, Phil.

mozwell

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Re: Tecky Q SMPSU
« Reply #1 on: September 19, 2011, 07:49:36 PM »
I know this is an old thread, but here is the the section of the article for the power supply.
It can supply 40mA at 260VDC out, but that may be the 12VAC plugpack limitation.
Slowly increase the load, monitoring the mosfet temperature & choke temperature. Measure the output DC volts. When the output volts starts to drop, we are out of regulation.
We can increase the wire size in the inductor, use a bigger mosfet & bigger heatsink on the mosfet to get more output current.

phatt

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Re: Tecky Q SMPSU
« Reply #2 on: September 23, 2011, 08:29:20 AM »

Hello mozwell,
 Thanks for the insight :tu: I think the LM7812 would limit things first but someone way back mentioned that if you bypass the reg chip then it maybe capable of a lot more than 40mA.
(assuming you use a decent DC supply of course)

I'm of the impression that the mosfet will not get hot if the switcher is working correctly but I'm only going by stuff I've read on Smode psu's.
This one is a little different as it uses an auto transformer.
Not having a scope to see real time what happens inside puts me back but I have fun blowing things up anyway. :o :duh

Anyways,,, A whole lot of other projects are in the way of real progress at the moment so this one is under the bench for latter.
Cheers, Phil.
ps, Your first post I notice?  So Welcome aboard. :)

 

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