SMPS for B+ ? it works! Rainy Day Project #1

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SMPS for B+ ? it works! Rainy Day Project #1

Postby EWBrown » Wed Dec 02, 2009 4:41 pm

I broached this topic earlier in the year, but until today, it just remained as mental vaporware.

Since I had pondered the availability of a "ready to play" HV DC SMPS for tube amp B+, and could not find anything suitable, I decided to try what is basically a "crazy mad scientist" eperiment.

Some time last year, I "rescued" a number of NIB 48VDC, 380 mA SMPS
from the dumpster at work. Along with numerous others including one for 12V, 5A DC. These 48VDC, 380 mA PSUs reportedly have an output impedance of approximately 10 ohms. Rock steady stuff!

I did some resistance checks and found that the secondary side of these SMPS were totally isolated from the AC primary side, with only a 0.1 uF, 1KV disc cap connected from the third wire safety ground to the DC negative side. So, stacking these things in series, for more voltage, theoretically, should work.

Since today was a gloomy coolish rainy day, and I had nothing much else better to do, I ended up hanging five of these supplies in series, for 240VDC, and connected a 6.8K, 2W resistor across each supply, just to act as "sharing" and bleeder resistors.

Upon the first power-up into no external load, I got a very steady 241VDC.

OK, lets hang a load on this "trainwreck"... I dug up a 40W, 230V Philips bulb, and connected it across the 241VDC. Powered it up, and it lit up as it should. Measured the DC voltage, still 241VDC, nice and steady, with approximately 167 mA current loading..

Left it to run for about an hour, the five SMPSs barely got warm.

OK, I really needed about 285VDC for a project, and 288VDC is more than close enough, so I added a sixth unit to the string, and got a nice steady (unloaded) 289VDC. The bulb drew about 200 mA, and was quite bright, but it took the "abuse" in stride. 58 watts from a 40 watt Philips bulb. :[ (banana)

While I was at it , I added the 12V, 5A PSU, and a 6A "FCC" type power line filter, and neatened up the wiring with some terminal strips.

Even out in the open, this thing is pretty quiet, RFI wise, and I was still able to hear an AM radio station on 550 KHz from about 60 miles away, with no interference.

Just in case there are any PSU failures, I still have another three "spares" should I need them.


Next step is to put this mess into a metal chassis, and filter the outgoing DC lines, so that all the switching EMI noise is contained.

I figure, take the 288VDC, then run it through a 1N5408 rectifier, into a hefty (220 uF or higher) 450VDC electrolytic, and then through a coaxial DC filter which I already have. The purpose of the diode is to prevent the HV electrolytic from back-loading into the series connected SMPS when it is powered down. Just an extra bit of added electrical safety...

I'll filter the 12VDC separately. I have a perfect size "dumpster" chassis to contain everything, and it will even come out looking fairly neat and clean, too.

Update 3/16/11:

I finally got this all assembled into the afore-mentioned "dumpster" chassis, it produces virtually no detectable RFI on a nearby AM radio, and outputs 288VDC @ 380 mA max, and 12VDC @ 5A max.

It all fits nicely inside of a 19X 1.5X 11 inch aluminum box, black powder--coated, the DC is brought out on a six screw terminal block on the back. I still have to add the DC coaxial filters, if I decide that they are really needed, and so far it appears that they probably won't be necessary.
I used a 6 amp AC input RFI filter which really does a good job of keeping the switcher noise from conducting back out on to the power line.

The fuse and AC power switch are on the back, and the front panel is "clean", though I may add a couple of pilot lights for the 12V and 288V DC.

I still have to add the 1N5408 "safety" rectifier and the hefty electrolytic cap, though they may just go into the amp or device under test, instead.

I could build up a suitable 12V6GT / 12SL7 PPP amp into another of these dumpster chassis, and mount it on top of the PSU, and have a nice clean looking, if not somewhat over-sized 14-28WPC PP amp. Or go crazy with a boatload of 13EM7s (666) ;) (lol)

If not that, then it will serve as a convenient bench- test power supply for future tubular projects.

/ed B
Last edited by EWBrown on Mon Aug 08, 2016 5:44 pm, edited 8 times in total.
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Postby nyazzip » Wed Dec 02, 2009 7:36 pm

isn't that how they make inverter welders?
<i>the poor craftsman blames his tools</i>
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Postby Geek » Tue Jun 08, 2010 12:42 am

halumori wrote:My smps damage regularly 3 to 4 time in a month? I have a new pc duel core2. My smps damage regularly 3 to 4 time in a month. What is the reason for that? Please help me.


Respond to this post if you are not a spam bot looking to "mark" a site.
(sorry, I've seens posts like this too many times)

Cheers!
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Postby Writer Frog » Tue Jun 08, 2010 6:49 pm

Image
Sorry! 8^)
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Postby EWBrown » Mon Mar 05, 2012 12:21 pm

Still, no pics, it's just a fairly palin looking black metal box, and it would be a real "bear" to open it up for a" gut shot".

update: I opened up the beast, in order to install some more RFI filtering on the HV DC side, , and shot a couple of pics, I'll post them in the near future.

Warning, it's kinda ugly in there =:o ;) (lol)

But I just received this from Joe, about another diy'er took this approach of stacking up 48V SMPS to a new, daring extreme, with eighteen of them connected in series! =:o for an 868 VDC power supply (770V B+, and -96V for the GM70 grid bias)

http://greenvalve.wordpress.com/2011/07/11/smps-for-b/

where eagles dare....


/ed B
Last edited by EWBrown on Mon Mar 05, 2012 9:07 pm, edited 3 times in total.
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Postby kheper » Mon Mar 05, 2012 3:30 pm

It would be nice to do some A/B tests with the SMPS and a "normal" 288V @ 380ma supply. Or, an SMPS feeding one channel and a "normal" supply feeding the other on monoblocks.

The size of 18 units being stacked may be prohibitive for some.

SMPS (laptop) supplies are used for class "D" and class "T" chip amps, because they are cheap and the voltages they put out are within the chips' supply ranges. Nobody really complains about noise coming from the SMPS energizing these amps.
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Postby greenvalve » Sat May 19, 2012 2:56 pm

Some pics of the final product for you guys.

http://greenvalve.wordpress.com/the-maxim-gm70/

Thanks, and keep on having fun! ;)
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Postby azazello » Sun May 20, 2012 1:31 am

I thing, GM70 will sound better with +U about 1100-1200 v /according advices of my russian tube guys/.
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Postby EWBrown » Sun May 20, 2012 8:24 pm

GM70 is a lot like the much older (1940s vintage) power triodes 211, 845 and 276A, they are happy with B+ of 1200 to 1400VDC, at 800V, they just don't achieve their full potential.

/ed B in NC
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Postby greenvalve » Sun May 20, 2012 11:32 pm

Thanks for the tip guys.

Really the graphite plate GM70 did not come alive until 1500V in A1. 1200V was just OK. The copper plate GM70 sounds good at 1200V but if you allow a little grid current to flow, dynamics become startling with just 677V. You need a stout bias supply that can source some real current to accomplish that. I have never seen any russian GM70 amp that could source current to the GM70 grid. ;)
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Postby EWBrown » Mon May 21, 2012 2:41 pm

I've found some 20VDC, 6A switcher "bricks" for use with some laptop PCs, those would be idea for lighting up the GM70 filaments.

I have three of these, and gave a few of them to Gary Kaufman for his (yet to be completed) GM70 amp build, a few years ago.

These particular "bricks" have a small and very quiet cooling fan, just enough to keep them cool under full DC l loading conditions)

/ed B
Last edited by EWBrown on Wed Feb 25, 2015 9:08 pm, edited 1 time in total.
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Re: SMPS for B+ ? it works! Rainy Day Project #1

Postby macm75 » Fri Dec 21, 2012 11:22 pm

Hello Ed,
I am a follower of Greenvalve and replaced my "traditional" supply with SMPS's for my SE 56 DC 46 amp - 9 48V (432V) in series - probably the same model ones you used - on for hours at a time over about a year and no problems.
I use another 4 as B+ for a single tube transformer output headphone amp - also uses a SMPS plus RC filter for the IDHT heaters.
I cannot get these amps this dead quiet and dynamic sounding with transformers, tube/ss rectification, and LCLC filtering.

All this talk about noise and SMPS's - I just don't get it. In particular, my headphone amp - when it's on and volume pot at zero - you would think it was a dead box. (btw, I did have an experience with using an SMPS as heater supply and heard a lot of noise - not sure why I did this but I ripped off the ground plug on the 120VAC in and the noise went away)

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Re: SMPS for B+ ? it works! Rainy Day Project #1

Postby EWBrown » Wed Feb 25, 2015 9:07 pm

Image

Here, at long last, are a couple of pics of this PSU:

Gut shot

Image

top view

Image
Last edited by EWBrown on Mon Aug 08, 2016 11:42 am, edited 1 time in total.
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Re: SMPS for B+ ? it works! Rainy Day Project #1

Postby Geek » Wed Feb 25, 2015 10:43 pm

That's mad... I love it! :)) [:)
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Re: SMPS for B+ ? it works! Rainy Day Project #1

Postby TomMcNally » Thu Feb 26, 2015 10:59 am

Wow ! I just found 7 brand new 48 volt 1/2 amp supplies in the storage room. 336 volts !
Prolly just duct tape 'em together behind the amp. Hmmm ... p[

What's the other one for Ed ? Fils ?
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