DC supply for Vacuum tube filaments (2/2)
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- Опубліковано 27 лип 2024
- #160 This time I build and test the circuit I simulated in a previous video. As always, real life is not exactly as the simulator says it will be... but its close enough. As with any interesting circuit, there are a few hiccups but it turns out well in the end.
Schematic: drive.google.com/file/d/11WIE...
Used Datasheet:
www.st.com/resource/en/datash...
Tube data book: Radioamatorok Zsebkonyve, Magyari Bela, 1967
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Very informative👍
Howdy.
I would call this true gourmet electronics. The persistence of vision !!!
For myself I would probably settle for a Schottky bridge and a two or three legged CRC filter. I would use a 6V2 zener diode at the end. The zener I would say is mandatory not to overload filaments when commissioning one tube at a time.
High Regards.
The LDO regulators for high currents are quite expensive. For just $2 one may get a DC-DC 5A convertor designed for battery charging. It has voltage regulation and current limiting. It's voltage drop is reasonably small (about 1 volt) even at high currents. The current limiting will come very handy to avoid the initial peak of the current, and warm up the filaments slowly and safely. It's 150 KHz noise is not a problem for audio equipment as it feeds into the isolated filaments and will roughly have the same effect on the sound as any of the room LCD lights.
Great detail, thank you
Thanks for the video.👍🏻
The filaments are basically for 6v3 A.C.@ 50/60Hz..where the worst case maximum peak in rush current is ,if it's switched on @ peak of wave will last only for two or three millisecs. only.....whereas in this dc. ckt. the
peak inrush current , (though @ slightly reduced start voltage ) is sustained for longer duration..i.e .3-5 seconds or more....,until the filament reaches its high temp. resistance value..,...
...implimenting an electronically controlled dc voltage...A better option would be a current
controlled soft starter ...or simpler still , two suitably selected N.T.C. 's , one in each leg of
either positive or negative rectifier diodes , each managing one half of AC cycle ... 👍
Excellent! Thank you.
Be careful with C2. This one is inside the feedback loop. So it might cause oscillations or poor regulation because it makes the loop very slow. I usually use a pnp on the feedback resistor R2 to ground. Or better is to use the enable pin if possible.
Instead of the large inductor I would have used a capacitance multiplier. Although in general I don't think it's really needed.
A capacitance multiplier has a too large voltage drop. So it cannot be used in this situation. We want the voltage drop to be as low as possible.
I think a safer soft-start could be implemented by using bjt transistor inplace of capacitor, and a much smaller capacitor with huge resistor to the base of bjt.
bravo!
Interesting video. But I don't really like the way the soft start is done. We could just use a Nmosfet on the negative supply of the load with a RC powering the gate. It would turn on slowly. This avoid playing with the regulator's feedback which could have side effects.
Interesting. What do you mean with 'negative supply'? Ground?
@@breedj1 between the - side of load and ground. The load is not directly connected to ground anymore.
The Nmos circuit you proposed will probably work well! I guess I went with this approach since the load (the filament) is very static - no load variations occur over time so you don't need a fast loop response in the regulator.
Nice, those high current Regulators and others getting expensive these days. I did this in a classic way with opamp, reference and MosFet. I doubled the rectified voltage with a LT1054 or a little DCDC Converter to supply the opamp and the reference and have enough headroom for the MosFet and used a low Vgs on type like the IRL540N. Sure a tiny bit more complicated but works fine. Thanks for the video!
To get a higher voltage for OPAMP usually is enough a voltage doubler with just a capacitor and diodes from the same iron core transformer winding and lm317 or simple zenner. DC-DC adds a noise
There might be a simple explanation for that inductor thing: your power coming from the wall is not sinusoidal. Where I live, for example, voltage peaks are chopped off flat.
As always a good job!
Please video on using CC source.
Need for larger tubes like GM70 (20V / 3A). Thank you in advance.
I guess your transformer has a significant amount of leakage inductance which had much the same effect as your big choke.
I think you are right! In the simulations, I never took into account the non-ideal elements of the power supply - I only used an ideal voltage source.
Filaments are designed to run on clean AC. Using DC introduces problems that don't exist otherwise, especially for directly heated filaments - the polarity has to be reversed periodically to prevent the cathode from being used unevenly. For indirectly heated cathodes, the output of a regulator is a far cry from pure DC. At least some of that random noise will be picked up by the grid and amplified.
Very good video, and interesting topic - LDO for vacuum tubes filaments.
I'm pretty sure it's possible to build the same from gelly-bean/dirt-cheap components, is it possible for part 3? ;)
The decision to go for LDO or just a regular linear regulator has to do with voltage drop; if you have enough headroom, no point in using the LDO. Sure you can build a regulator from components, but with bit of component hunting, I think the dedicated regulator component will be cheaper, or at least you can be far more confident it will work as expected.
Why not make use of a "Latour doubler" from 6.3V AC to get more headroom at the regulator input and a simpler (and cheaper) LDO regulator as the LD1085 (rated 3A), plus a simple soft start (RC network and Power NPN) ahead ?
I did not want to use a voltage doubler to improve efficiency - with the doubler, more than half of the input power would have been wasted as heat; like this the efficiency is somewhat better.
@@FesZElectronics Yes, if efficiency is the prime keypoint, I understand your point of view , although aiming at efficiency with tube amplifiers seems worthless. As I'm facing issues with "rumble" on one of my tube amps that disapears when driving the heaters with an external linear PS , I'm really interested in your work. Thanks for your answer !
one question: what is the power value dissipated on heatsink?
Being an transformer iron core for your inductor, should it not be gapped to keep it from saturating? Being it's behaving so much like a wire, I'm wondering if that is happening.
Iron can handle 7times more current than ferrite even without an air gap. With such a core size I believe it can handle 5A. The whole reason is to avoid EMI emissions, so try to avoid air gaps.
Can someone name equivalents for the schottky diodes and mosfets?