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SMPS for vacuum tube power amplifiers.(status: back at it)

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TimNJ:
I think you are smart to not inflate the scope of your project by using an off-the-shelf transformer. My experience in designing SMPS transformers is fairly limited, but I can tell you a few things.

1.) Getting a first “working” prototype is not that hard, even if you have little experience. But, optimizing the transformer can be quite a thought experiment, forcing you to think in terms of magnetic/electric fields, circulating currents and so on.

2.) Hand winding a transformer is not hard at all! Getting your hands on all the supplies can be a bit challenging, but these days, you can buy sample kits on eBay inexpensively. For example, you might want various diameters of enameled wire, litz wire, triple insulated wire (TIW), TIW litz, poly tape (the yellow stuff), Teflon tube etc.

It’s probably not worth the trouble at the moment. But sometime in the future, it may be worth it to give custom a shot.

SK_Caterpilar_SK:

--- Quote from: TimNJ on April 20, 2019, 03:52:01 pm ---I think you are smart to not inflate the scope of your project by using an off-the-shelf transformer. My experience in designing SMPS transformers is fairly limited, but I can tell you a few things.

1.) Getting a first “working” prototype is not that hard, even if you have little experience. But, optimizing the transformer can be quite a thought experiment, forcing you to think in terms of magnetic/electric fields, circulating currents and so on.

2.) Hand winding a transformer is not hard at all! Getting your hands on all the supplies can be a bit challenging, but these days, you can buy sample kits on eBay inexpensively. For example, you might want various diameters of enameled wire, litz wire, triple insulated wire (TIW), TIW litz, poly tape (the yellow stuff), Teflon tube etc.

It’s probably not worth the trouble at the moment. But sometime in the future, it may be worth it to give custom a shot.

--- End quote ---

Very well said, to say my first ever HV experiment was a hand wound transformer and it was working better than expected but it definitely wasnt powerfull enought- 10W is not really useable for anything other than preamps and the ferrite was not glued and it was screming soo..but it worked. I much rather use the off the shelf stuff because the specifications are already there measured and I only work with those value instead of guesstimating and I really cant calculate that stuff, wire width inductances coupling coeficient and other stuff. So I did make a hand wound one but it was less than ideal. And also the enameled wires are not cheap. Their maybe look cheap for you but for some reason all the wires I would like to buy have either crazy postage and or crazy price.

About the overinflation- its MUCH cheaper for me to buy a switching transformer that was designed more or less for the application im using it at. And a whole lot simpler. The first transformer I got I payed for and then now looking at the transformers I realised I can ask coilcraft for samples so I did and hopefully, the transformers will arrive so I can have test PCBs to experiment with.

T3sl4co1l:
XFMRS may be more likely to prototype small quantities, or others that I've since forgotten; and also, any local motor rewind shop will likely have the tools and materials to do the same.

Don't expect an amazing design from any of these sources, though -- to get that, you'll have to supply at least a basic drawing, preferably a drawing accurate down to the last turn, and designed based on transmission line transformer principles, and, probably, based on a lot of experience too.

Custom voltages don't preclude the use of commercial parts, but it does severely limit the choice and performance.  For multiple outputs, consider multiple single-output transformers wired in parallel (parallel primaries, of course).  Any extra aux windings, of course, just leave open.  (By the way, don't be tempted to use one as secondary-side aux: the pri-aux insulation is usually not full reinforced.  If the datasheet says it is reinforced, though, that's fair game!)

Tim

SK_Caterpilar_SK:

--- Quote from: T3sl4co1l on April 21, 2019, 12:53:02 am ---XFMRS may be more likely to prototype small quantities, or others that I've since forgotten; and also, any local motor rewind shop will likely have the tools and materials to do the same.

Don't expect an amazing design from any of these sources, though -- to get that, you'll have to supply at least a basic drawing, preferably a drawing accurate down to the last turn, and designed based on transmission line transformer principles, and, probably, based on a lot of experience too.

Custom voltages don't preclude the use of commercial parts, but it does severely limit the choice and performance.  For multiple outputs, consider multiple single-output transformers wired in parallel (parallel primaries, of course).  Any extra aux windings, of course, just leave open.  (By the way, don't be tempted to use one as secondary-side aux: the pri-aux insulation is usually not full reinforced.  If the datasheet says it is reinforced, though, that's fair game!)

Tim

--- End quote ---

Yeah about the aux windings- no I only use the transofmers as specified in the datasheet. Now that im thinking about it, a all in one powersupply would be the ideal thing to do. 6,3V 35W for heaters, 400-600V for anodes about 80W, and another aux that would deliver almost no current , in some tube amps there is a -50V supply for biasing the output tubes. In cathode biased circuits you only need the heater and the HV, but cathode biased amps have their drawbacks, I would definitely want to try and make a fixed bias amp at some point. So yeah 6,3V 35W, -50V 5W, 400-600V anode voltage at about 80W of power would be ideal, a replacement compatible with most common amplifiers.

I would like to do that but I have no idea how to calculate SMPS transformers at all and I cant really find literature that would explain it to me at the level of my understanding. But I will very likely do something like that as a grand finale for the PSU.

SK_Caterpilar_SK:
Since I found that blowing with a fan on my original HV PSU was UNACCEPTABLE I went and redesigned the whole thing. This time using the TL494 as the controller. Operating frequiency will be set to 50kHz. Also have a soft start function, NO OPTO ISOLATION YET. Im still working on the mains powered solution.

So basically I want to listen to my amplifier while I work on its powersupply some more without that fan blowing on the PCB lol. The reason the fan has to blow on the PCB is because i made the traces to thin (2mm) for the required power about 60W. It would require at least a 3,5mm trace with...but not to worry this time I bombproofed the thing and went 6mm trace width where I could and massive ground and power planes. And my pull is to tin it with liquid tin or the traditional handsoldering, depends how fast I can get it done :D

The TL494 should give a way more stable output that I could ever get with my hacked together quad op amp controller I designed previously.

The TL494 also extends the operating voltage up to 40V. About the efficiency- I have no idea what to expect so far, I will find out after loading and measuring the characteristics of the powersupply.

(The board layout is not done completely.)

EDIT: The IGBT will be mounted vertically to a heatsing not to the PCB (its also related to the not completeness of the board..)

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