SMPS for tube HT

[ruffrecords]

Indeed it is.  There are a plethora of inexpensive 12V high current wall adapters on the market because of the popularity of LED strips.  I purchased mine on Amazon for about $15, and it even came with European plugs.

Excellent. I may try a couple.

This isn't so much an issue with PWM buck topologies, because the FET and inductor are both in series with the load.  Essentially the controller turns on the FET until the output voltage rises to the set point at which point it starts to PWM average the output.  I could see what you describe happening with a boost module, since it relies on charging the output cap through a diode after the FET switches off.  However I've never had any problems with using the raw LED supply for the heaters on any of the tubes I've tested so far.

I've probably logged 200+ hours on the scope with my design and would be happy to help if you need it.  I've tested half a dozen FET's, and since the current requirements for tube gain stages are modest, you don't need to use the $15 ones either.

I suspect our requirements may differ in some respects. I am mostly interested in powering tube mixers, or at the very least a 3U rack containing a number of tube modules. The heater current of the 3U rack is about 2A at 12V and for the mixer is can be several times this (typically 10A). Both Holger Classen and I have tried AC/DC  SMPS for  heaters at these sort of currents and have only been able to get them to fire up the heaters if the SMPS is heavily over rated. Simple ones I used years ago which go into SC current limit when presented with tube heaters can never input enough current to get the heaters warm enough to exit current limit even if well over rated. Only recently did I look at this again and came across hiccup mode which can cope with large capacitive loads which require similarly large inrush currents to tubes. I have had success with versions of these from Mean Well. At present I have a 100W unit that will successfully light up 4A of heaters at 12V. I am not yet convinced a 50W unit would do so but I would be very pleased if it could be so.

Thank you for the kind offer to help out with the design. I will certainly take you up on that.

Cheers

Ian

 

[Matador]

Hmm - what about a standard PC power supply? Most of the PC supplies that support the EPS12V standard have hefty 12V rails, and are super inexpensive.  Would make servicing easy as well.  8)

Here's one for example: Corsair VS400  - $34.99 on Amazon

Can do 32A on a +12VDC rail.

 

[ruffrecords]

Hmm - what about a standard PC power supply? Most of the PC supplies that support the EPS12V standard have hefty 12V rails, and are super inexpensive.  Would make servicing easy as well.  8)
t come on.
Here's one for example: Corsair VS400  - $34.99 on Amazon

Can do 32A on a +12VDC rail.

That is an interesting idea. I will look into it. I would prefer fan-less operation but the Corsair's  one is thermally controlled so it wold probably not come on. Thanks for the tip.

Cheers

Ian

 

[Tubetec]

They have a graph for output current vs fan noise for the Vs-400 here
http://www.corsair.com/en-us/vs-series-vs400-400-watt-80-plus-white-certified-psu-na
Looks like the fan runs continuously ,speeding up a bit once you go over 50% load, overall efficiency is best around the 50% point too

 

[ruffrecords]

They have a graph for output current vs fan noise for the Vs-400 here
http://www.corsair.com/en-us/vs-series-vs400-400-watt-80-plus-white-certified-psu-na
Looks like the fan runs continuously ,speeding up a bit once you go over 50% load, overall efficiency is best around the 50% point too

OK, thanks for that. The 400W version does not seem to be available in the UK but the 450W one is. I might just buy one to try out. Which output is used for regulation? Do I need to ensure that output has some sort of minimum load to ensure regulation?

Cheers

Ian

 

[Tubetec]

The question of keeping all the rails happy with a minimum load came to mind also .
I re-jigged an older X-box psu to power a battery charger a while back ,worked great, theres a wire that gets connected to the 5 volt rail to power up the main 12 volt section, I put a toggle switch in to do this ,one day I plugged in the supply without anything connected ,toggle was in the on position ,Bzzzt, fused it out . The internals of those particular units are coated in a white acrylic substance of some kind ,so doesnt lend itself to easy servicing .They can be found very cheaply and in abundance now though as that version of the x box was prone to heat related faults on the motherboard.

 

[Matador]

Most PC power supplies I've tested needed a minimum load (somewhere in the 100-500mA range on one of the rails), but I'm guessing your heater supplies would more than make up for this.  Also, that VS series that I pointed you too was their cheapest line: they have better efficiency models and even ones with no fan.  In the HX series (the ones I use in my PC's and power supplies), the fan doesn't run until about 40% load, and only if the internal temp rises some threshold above ambient.

 

[ruffrecords]

Most PC power supplies I've tested needed a minimum load (somewhere in the 100-500mA range on one of the rails), but I'm guessing your heater supplies would more than make up for this.  Also, that VS series that I pointed you too was their cheapest line: they have better efficiency models and even ones with no fan.  In the HX series (the ones I use in my PC's and power supplies), the fan doesn't run until about 40% load, and only if the internal temp rises some threshold above ambient.

Thanks for the info. I see more research ahead!

Cheers

Ian

 

[TheJames]

Picking this conversation back up...

I'm sure with some effort one could design a SMPS for a tube output stage (like a pair of 6l6's).  I guess the question is more would it be economical to do so than using a traditional PSU with a big power transformer?

 

[ruffrecords]

Picking this conversation back up...

I'm sure with some effort one could design a SMPS for a tube output stage (like a pair of 6l6's).  I guess the question is more would it be economical to do so than using a traditional PSU with a big power transformer?

I recently ordered the MeanWell SMPS mentioned in the opening post. It cost me £28.66. Probably less than than the big power transformer.

Cheers

ian

 

[pvision]

When using a PC power supply you have a 5 VDC output with lots of current capacity. Can you use that for heaters? Maybe with a small tweak to the voltage?

Nick Froome

 

[ruffrecords]

When using a PC power supply you have a 5 VDC output with lots of current capacity. Can you use that for heaters? Maybe with a small tweak to the voltage?

Nick Froome

I am sure that is possible for many projects. For mixers I use 12V heaters because it halves the current requirements. Even at 12V, Holger's 12 into 2 tube mixer needed a 10 amp heater supply. Fortunately 12V SMPS are plentiful.

Cheers

Ian

 

[TheJames]

Hey Ian...I don't see anything on Mean Well's site search that seems to due 300V+....Do you have a series or model I can maybe dig further on?

Thanks!!

 

[ruffrecords]

Hey Ian...I don't see anything on Mean Well's site search that seems to due 300V+....Do you have a series or model I can maybe dig further on?

Thanks!!

ELG-150-C500A-3Y

It an LED power supply but it seems to give 300V dc up to 500mA. I have one on order.

Cheers

Ian

 

[TheJames]

Some of those LED PSU's are pretty intense.  I noticed that the voltage was listed as "open circuit" and that the current regulation is typically well below the listed voltage.

Pretty interesting find.  I never would have thought to look at an LED supply.

 

[ruffrecords]

Some of those LED PSU's are pretty intense.  I noticed that the voltage was listed as "open circuit" and that the current regulation is typically well below the listed voltage.

Pretty interesting find.  I never would have thought to look at an LED supply.

I cannot take credit for finding it. Another groupDIY use found it. Like you I had scoured the MeanWell catalogue and found nothing I could use for HT. The groupDIY member who has tried one said the output voltage remained steady up to several hundred mA of load. There was some ripple but much less than you would see on a tube power amp supply and low enough that a simple LC filter should be able to remove it. I cannot rememeber if his posts were in this thread or another one. (I plead old age).

Cheers

Ian

 

[wlinart]

Just bumping an old thread. i saw this SMPS on aliexpress: https://www.aliexpress.com/item/4001003220219.html
Looks like a nice psu for tube amps, heaters and HT at the same time for less than €30.
Could be nice, couldn't it?

 

[ruffrecords]

Just bumping an old thread. i saw this SMPS on aliexpress: https://www.aliexpress.com/item/4001003220219.html
Looks like a nice psu for tube amps, heaters and HT at the same time for less than €30.
Could be nice, couldn't it?

This looks like an improved version of  one I tried a year or so ago.  Mine has the same spec but a slightly different foot print being 120mm long and 55mm wide. I found that the heater voltage was regulated but the HT was not. Also the HT ripple is still too high for preamp or mixer use but probably OK for a power amp which is what I suspect these are aimed at. Also it will probably struggle to power up into a 4.5A heater load because cold heaters will want to draw at least twice this amount initially. It is not clear what current limiting if any is included so this could be catastrophic.

Cheers

Ian

Cheers

Ian

 

[trobbins]

Ian, why did you say the HT ripple was too high - was that mains frequency related? 

Did the heaters eventually power up in the earlier version? I would expect that any such switchmode heater supply would hiccup its way through initial powering of the heaters - that is a common control method and has no concern for the application - I would be amazed if it was 'catastrophic' as that just doesn't sound like any switchmode control mechanism used nowadays.

The hassle I have, and the real concern is that the product has met no electrical safety standards, and in many countries would not be allowed to be used.  So it would just be for DIYers with a death wish, as no commercial product could use it.

 

[emrr]

The hassle I have, and the real concern is that the product has met no electrical safety standards, and in many countries would not be allowed to be used.  So it would just be for DIYers with a death wish, as no commercial product could use it.

I wonder when that axe is gonna fall, there are so many boutique shops selling finished audio electronics with zero certifications.