6v smps

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ed
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6v smps

Post by ed » Fri Nov 29, 2019 7:52 pm

Has anybody come across a 6v smps(the meanwell frame type). I've spent a good while searching and can't find anything. There are 5v, 7.5v, 9v and 12v but no 6v. I'm sure I remember seeing 6v versions in the past.

I wanted to try direct heating without stepping down or using regs. There are a few web sites showing how to frig existing units to produce variable voltage but they are all complicated...and complicated was what I was trying to avoid.
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Re: 6v smps

Post by Ray P » Fri Nov 29, 2019 9:38 pm

Assuming you're looking to power two 6.3V filaments, you could use a 12V SMPS and run the filaments in series?

This Mean Well SMPS looks like it'll do the trick and the output voltage is adjustable between 10.8VDC and 13.2VDC;

https://uk.farnell.com/mean-well/rs-25- ... dp/2816009

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Re: 6v smps

Post by Mike H » Fri Nov 29, 2019 10:05 pm

If it helps, I'm going to try 12V output net book SMPS + a series resistor for my 801A's, admittedly 7.5V not 6.

Don't hold your breath tho I bought them off Maplin yonks ago and still not got anything together yet. :D

But I now have the resistors :lol:
 
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Re: 6v smps

Post by simon » Fri Nov 29, 2019 11:41 pm

If I'm thinking of the right bit of kit don't they have a multi turn pot to adjust the volume? So 7.5V can be set to 6V. I run my 24V cheapo SMPS at 19V for the class D amps.

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Re: 6v smps

Post by ed » Sat Nov 30, 2019 12:16 am

thanks guys...

I am already using 2 x 12v with coleman regs. The big ones are too bulky and they need monster heat sinks...I wanted to try and simplify things.

My head doesn't seem to like the idea of running 2 DHTs with one PS, I can't see how that would work.

and 10% off 7.5 wouldn't get me safely low enough......actually with the 12s and 24s I've got I've never actually manged to get 10% variation.

I might be dreaming but it's nice to think those 6v units are still out there and I just haven't found them yet.
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Re: 6v smps

Post by Ray P » Sat Nov 30, 2019 6:45 am

ed wrote:
Sat Nov 30, 2019 12:16 am
My head doesn't seem to like the idea of running 2 DHTs with one PS, I can't see how that would work.
Ah! I had assumed indirectly heated valves so a single supply isn't such a good idea.

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Re: 6v smps

Post by pre65 » Sat Nov 30, 2019 10:10 am

I'd go for 7.5v, and use the inbuilt pot + external resistor to achieve 6v.

My theory is that DHT valve performance is directly related to the "quality" of the filament supply.

Have you got any filament chokes in the spares box ?
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Re: 6v smps

Post by izzy wizzy » Sat Nov 30, 2019 11:22 am

I was using a 24V Meanwell SMPS on the GM70 for a bit. I used dropper resistors in each leg to a CM choke and then the filament. They have adjustable output over quite a range for some of the models. Worked fairly well.

I found Meanwell Direct to have the best prices

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Re: 6v smps

Post by ed » Sat Nov 30, 2019 4:39 pm

I was just fiddling with what-ifs and I realised whatever I do I'm going to have to deal with some heat...

in the scenario below the 2 R12 droppers will be passing 4 amps so will need to be 5 watts each and then I'll bet they still get toasty...6v smps still looks like the best solution....unless I've missed something obvious
filaments.jpg
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Re: 6v smps

Post by izzy wizzy » Sat Nov 30, 2019 5:31 pm

I've used 2x5v SMPS in series to get 10v. Could you use 2x3.3v in series to get close to 6v?

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Re: 6v smps

Post by simon » Sat Nov 30, 2019 5:39 pm

Yes, I don't think there's really a way around heat if you want to regulate filaments. Better to embrace it!

6.3V @ 4A is "only" 25ishW. Shouldn't be too difficult, though it's the voltage drop across the regulating bit that needs the sinking. I've bolted mine to lengths of ally angle and never had a problem. The GM70s also had heatsinks and barely get warm.

You've had problems with yours though I know.

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Re: 6v smps

Post by Nick » Sat Nov 30, 2019 6:54 pm

Must be wrong but I make the dropper resistors 0.08 ohm each.

1.5 || 50 = 1.45 Ohm

6,3 / 1.45 = 4.35A

7 - 6.3 = 0.7V

0.7 / 4.35 = 0.16 Ohm

0.16 / 2 = 0.08 Ohm

0.08 * 4.35 * 4.35 = 1.52W
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Re: 6v smps

Post by ed » Sat Nov 30, 2019 9:44 pm

you're probably not wrong

I was messing about with a 7.5 volt meanwell and I ran all sorts of scenarios between 7v and 6.75v(10% which is the max adjustment). I just happen to have the spice model set at 7v when I took the snapshot.....

I did all my previous testing with a 6v 25w bulb, before I risked a 572 filament. This time I used a piece of paper and arrived at a 1r5 resistor to mimic the load(I used 6v and 4amps, cos I'm precise like that). It was close enough to see where all the heat goes, and how well I could minimise it.....

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Re: 6v smps

Post by Mike H » Tue Dec 03, 2019 10:00 pm

ed wrote:
Sat Nov 30, 2019 12:16 am
My head doesn't seem to like the idea of running 2 DHTs with one PS, I can't see how that would work.
Have to admit I'm the same. I feel each filament needs to be "free" to do its own thing. In series is possible but then same prob with grid bias, if like me you like cathode bias.


There is another possible issue I've just thought of, the 6V SMPS may not like the very low resistance of a cold filament and thinks it's a short so keeps dropping out.

However, you could use the 12V supply then follow it with relatively simple small buck converters, I even got some MC34063 chips to play with, but haven't done it yet. They'll only do 1 Amp tho unless an extra external transistor is added.
 
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Re: 6v smps

Post by izzy wizzy » Tue Dec 03, 2019 10:12 pm

The Meanwell SMPS I have overload on startup but recover and then startup slowly when driving the fils direct. I've had other SMPS fail to start after overload.

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