Switch Mode Powersupply for tube preamp, DIY.

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The schematic for the stock power supply is here
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The transformer coils have the Turns listen, times the strands that are in parallel.
The other number is the layer counting from the bobbin, I also used it as a phase dot, putting in on the side I'd put the phase dot on.
I'll draw out the primary circuit in a bit.
The driver IC is a KA1L0380R, fixed at 50khz.... at this point I'm desperate to get some kind of power supply working so I'll just stick with this not-ideal choice, I know it was working. :D

After looking at the numbers in every orientation there doesn't seem to be any correlation between anything and the V/turns ratio.
I'm just worried that the voltage will be WAY off for the HV winding, I'll use the heater winding for the voltage refrence so that's not a problem but the HV winding would be a problem if the V/T ratio suddenly jumps up or down as the turns go up.
 
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Well there's the entire schematic for the supply, minus the mains rectifier and power factor correction thingies.
Core is an EI33
 
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Ok I give up, after spending hours studying math and winding the transformer, it barely works, and by barely, it only works when there's around a 200mA load, no less, no more.
The original circuit was whack too, all the math was yelling at me to also rewind the primary and auxiliary windings but I refused, I didn't want to mess the primary up, but that perhaps would've made it work instead.
I'll probably revisit the circuit some day but as for this preamp, I guess I'll just have to go with that external power supply unit.
If anyone's interested in the winding layout (that did not work), from the core going out it was this:
25T Primary, ?turns aux, 4T*2 Heater, 4T*5 Heater 2, 25T Primary, 70T HV, 50T HV, 80T HV, 25T-CT-25T "Medium voltage".
The high voltage winding gave me like 20 volts just with the multimeter as a load. and the transformer got hot too so perhaps there was a short in the HV winding.
 
Ok I give up, after spending hours studying math and winding the transformer, it barely works, and by barely, it only works when there's around a 200mA load, no less, no more.

I made a SMPS for a Stereo EL84 PP Amplifier before, including transformer design, getting everything production reliable etc.. It was based on a similar IC (also QRP) but from Fairchild.

Primary and secondary windings must be interleaved and wound for low capacitance etc...

It worked great once fully done, but it was significantly non-trivial and took a lot of effort. Plenty of gotchas in this, definitely not something for casual dabbling.

Thor
 
Well a cathode follower has a lot of negative feedback, that's why the high anode impedance of the tube doesn't ruin the output impedance.
The 10K plate resistor will severely limit the output current of the WCF. The lower triode is the only load correction and even if it's in cutoff in order to supply more output current there's still the plate resistor and plate resistance in the way.

Trust me. I have lived this one. I think you're caught up in theory that doesn't account for the limited current. As I said, a P-P totem pole output will kick ass.

Again, best of luck.
 
The 10K plate resistor will severely limit the output current of the WCF. The lower triode is the only load correction and even if it's in cutoff in order to supply more output current there's still the plate resistor and plate resistance in the way.

Trust me. I have lived this one. I think you're caught up in theory that doesn't account for the limited current. As I said, a P-P totem pole output will kick ass.

Again, best of luck.
The anode impedance of a cathode follower only matters when the anode-cathode voltage is low, otherwise it works as a cathode follower - with it's low output impedance.
Driving the output stage so hard that the cathode voltage goes up nearly to B+, and the bottom stage goes into cutoff, doesn't seem very likely in a mic preamp. it would equal like 12.5V on the output, going into 600 ohms...
This is not a Rode microphone, I don't need an output stage that can drive 20 watts into 100 ohms :D
 

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