Its been a very long time ago since I am resisting te idea of using an SMPS for heating my tubes, but lately I am toying around really big flaments in the class of 10 to 30 amperes and the SPMS seems the way to go especially considering that SMPS technology has advanced alot. My initial tests with an old PC power supply are good, although alot of HF random noise is (checked this with my scope) present at the output of the supply but is not making its way at my speakers (ears anyway) at all.
So, my question is, has anybody any suggestion for lets say 5V 30-40A capable SMPS with good noise figures diy or ready made?
I checked and there seems to be a huge avalability of very good quality SMPSs from servers which seem excellently made, power factor corrected and very small too!
On the other hand maybe is time to start a colaborative project for a dedicated SPMS for our Tube experiments as SPMS technology seems very advanced and available too.
So, my question is, has anybody any suggestion for lets say 5V 30-40A capable SMPS with good noise figures diy or ready made?
I checked and there seems to be a huge avalability of very good quality SMPSs from servers which seem excellently made, power factor corrected and very small too!
On the other hand maybe is time to start a colaborative project for a dedicated SPMS for our Tube experiments as SPMS technology seems very advanced and available too.
run it through a 2 -5 uH air core inductor then into 4700 uf / 16 volt cap. Most of the noise will be gone. the real problem is that noise seeping into the audio input via RF propogation, moving the power supply away from the amp will eliminate this.
I used SMPS for several amps: 10V for GU-13, 20V for GK-71, as the result got compact amps with bright lamps! Also, silent DC for amps on 6P15P and 4P10S!
What noise? No noise if all wires are soldered in proper places, without weak signal sharing wires with dirty big currents - it is the common mistake that leads to noises fast recovery diodes, vacuum rectifiers!
What noise? No noise if all wires are soldered in proper places, without weak signal sharing wires with dirty big currents - it is the common mistake that leads to noises fast recovery diodes, vacuum rectifiers!
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Unique Tube Heater Supply
Unique Tube Heater Supply
I've always wanted to try SMPS for 6AS7G OTL designs, but the trouble is finding 6.3V @ 20-40A off-the-shelf. 5V is very common, as is 12V - but neither are exactly suitable. Even a 'small' OTL of that type needs 20A per channel, with mid-range designs needing 40A / chan.
One would think (...) that there must be a relatively simple way to tweak a 5V supply up to 6.3V (~20% increase) but I for one wouldn't know how. If it's as easy as locating a basic voltage reference (like a zener, etc) and altering the value, then that's pretty simple. But I don't know the first or second thing about SMPS designs such that I'd be able to do it.
It might also require changing a couple of output-side caps, if they're not at least 8-10V. But that's no great issue either.
One would think (...) that there must be a relatively simple way to tweak a 5V supply up to 6.3V (~20% increase) but I for one wouldn't know how. If it's as easy as locating a basic voltage reference (like a zener, etc) and altering the value, then that's pretty simple. But I don't know the first or second thing about SMPS designs such that I'd be able to do it.
It might also require changing a couple of output-side caps, if they're not at least 8-10V. But that's no great issue either.
Off line switchers can probably be modified for the correct output voltage by a change of the resistor divider in the voltage sense circuit.
Or you can put a linear post regulator after the switcher if you don;t mind burning up some Watts/
Or you can put a linear post regulator after the switcher if you don;t mind burning up some Watts/
Usually there is a TL431 with a voltage divider. I remove a SMD resistor, put a variable one, set voltage, then measure the pot's resistance and solder there some constant one, or 2 in parallel to get an exact 6.3 or 12.6V value.
What's stopping you from putting two heaters in series and use cheap-as-chips 12V SMPS? Slightly lower voltage for the heaters is good for longevity. Most SMPS i know can be tweaked for a bit more voltage anyway. Don't forget that you have less current for the heater wires to carry as well (translates to smaller gauge).
I'm using SMPS in my GM-70 ALL DHT project with no problem whatsoever. There is no noise at all. Amp has been measured with R&S Audio Analyzator.
Main thing is that for correct voltage I have additional RCRCRC filtering.
Main thing is that for correct voltage I have additional RCRCRC filtering.
So, all in all, let me carfy things about measured noise, when I said "alot of HF random noise" I meant about 700mVp-p at 0,5 μsec setting on my scope when the PS provided 5V @ 25A measured at the socket of the 304TL. On the other hand there is absolutely no noise at my tannoy speakers even 20cm away. What I am asking is your proposal of the PS you actually use successfully as the one I am currently use is big and old. If you check ebay, alot of 500-1000W excellent PSs are available at less than 50$ with the extra bonus of small size and PFC too. Problem I noticed is that almost all of these are 12V 30-100A and none 5V at more than 5-10A. Modifying these for 5V operation is very hard as these are truly very high tech designs with all controlling circuitry very small SMDs.
usually the problem of RF propagation owes to inadvertent "turn on" of PN junctions in low noise circuitry -- leading to "unexplained distortion" from non-linear behavior, as Analog Devices puts it. Not to big a problem for tube stuff i would hope.
Of course, back in the day you could cause a lot of problems with TV front ends if you didn't filter the output of your ham transmitter!
7.5v switching power supplies are a commodity item and they generally have an adjustment trimpot.
This 46-amp 7.5v (nominal) SMPS can be adjusted from 6v to 9v:
http://www.mouser.com/ProductDetail...=sGAEpiMZZMsPs3th5F8koPF2exM897jTt6agwSuewXQ=
Or, tube design allowing, you can run pairs of tubes with their heaters in series and use a 12v supply.
I didn't even think to look at Mouser -- here's a 6V 50W supply which can be adjusted +/- 10% http://www.mouser.com/ProductDetail...GAEpiMZZMsPs3th5F8koFzyKJ2w%2burhd5suldYEHqQ=
Would appear ideal for Pete Millett's "Engineers Amplifier" which has 4 6JN6 + 4 6CB6 = 6.3V @6A
Would appear ideal for Pete Millett's "Engineers Amplifier" which has 4 6JN6 + 4 6CB6 = 6.3V @6A
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Not usually. Yes, sometimes they have Zener and triac that engage before the voltage you want 😀
I grabbed a smps I have and tried the output adjustment. On the 5volt output it says it can be adjusted to max 6.0volts. Well it went to 6.25volts. For fun I hooked it up on my pre since theres an easy to get to umbilical connection. Even tho the b+ is only 65volts it sound very good. 6BX7 tube.so if u get 5volt smps with some adj it may well go to just over 6volts.
Of course I am ignoring the hf noise from the way over size smps going burst on me. But I may just keep the 6volt smps on heater and use the old linear on b+.
Of course I am ignoring the hf noise from the way over size smps going burst on me. But I may just keep the 6volt smps on heater and use the old linear on b+.
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I use a pair of nice 24V switchers with Rod Coleman regs after them for my GM70 amp.
I lowered the the output voltage slightly using the mentioned trick with the output sensing potential divider. I only dropped it by a volt or so to minimise dissipation in the linear regulators. No noise whatsoever.
Something else to watch for with switchers is that they often have an X class capacitor from the negative output to mains earth. This can introduce noise and if you want a true floating output will need to be removed. Trouble with that is that the leakage reactance of the tiny switch mode transformers is quite high. So that also introduces noise. Try it with and without the cap. Also check that without the cap the output doesn't drift up to around half mains voltage due to leakage capacitance in the transformer.
Cheers
Matt
I lowered the the output voltage slightly using the mentioned trick with the output sensing potential divider. I only dropped it by a volt or so to minimise dissipation in the linear regulators. No noise whatsoever.
Something else to watch for with switchers is that they often have an X class capacitor from the negative output to mains earth. This can introduce noise and if you want a true floating output will need to be removed. Trouble with that is that the leakage reactance of the tiny switch mode transformers is quite high. So that also introduces noise. Try it with and without the cap. Also check that without the cap the output doesn't drift up to around half mains voltage due to leakage capacitance in the transformer.
Cheers
Matt
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Specifically the OP was asking about Directly heated tubes... I would suggest floating the supply. As stocktrader200 said use a small choke into a good sized cap (I would go with 10000uf 16v) and ground reference it from side to side with resistors. Keep in mind that too big of an input choke will cause instabilities in the SMPS.
Cheers.
Cheers.