thebugger

modified 9 years ago

Vacuum Tube Power Supply

196

02:55:47

This is how I'm thinking of rebuilding it. I think this is the perfect filter, but the voltage drop is a little too much. Most tubes i use, work on higher voltages of 300V, but i guess 250V or 300V isn't much of a difference. The ripple rejection is -67dB. The 760ohm resistor is 2W and the 170ohm resistor 1/2W. Since I'll be using this supply for almost every load, and a typical amplifier will have a varying draw I'd say for the 760ohm resistor 5W and for the 170ohm one 2W would be best. 

published 10 years ago

WTFCircuit

10 years ago

How big is a 4H inductor?

giomix

10 years ago

@wtfc : it is depending from maximum current. Usually current can be 60 - 100 mA and choke is like a little transformer , around 6 x 4 x 5 centimeters

WTFCircuit

10 years ago

Nice and big

giomix

10 years ago

@thebugger: thanks for your schema, it's simple and efficient. I have a question for you: using a center tapped transformer and two diodes it is possible obtain HT anodic voltage fully rectified and negative voltage respect ground for a tube grid, simply using a resistance partition between HT and center and a diodes and capacitor. Do you know a way to obtain this using a no-center tapped transformer and four diodes? Thanks.

hurz

10 years ago

http://everycircuit.com/circuit/6278769735106560

thebugger

10 years ago

Hurz thanks for the proposal but the tranaformer resistance is 125ohm, can't do anything about it except add a few hundred ohm resistance in series. And i prefer 1k because I'm currently using an EL82 and it's maximum sustained plate voltage is 250V and this provides the needex drop. I guess it wouldn't be a problem to run it at 300V but i want to preserve the tubes as long as possible, so im running on nominal parameters. Gio

thebugger

10 years ago

@Giomix, just dont use the central tap. Use the other two points with a bridge. If the voltage is too high between these two points, then you must disconnect the central point, detaching the two windings from one another, and use whichever suits your requirements best

hurz

10 years ago

@thebugger, yes i know 125Ohm is dc resistance of the coil, that was clear. 4H and 47uF needs 580Ohm for critical dampening. 125ohm you get for free as i said. The rest you can and should add or you get an unstable filter behaviour. And together with the notch i propose you can even lower the total resistance by half the 1kohm. Just a proposal....

thebugger

10 years ago

Yes, thatnks for the proposal. It's appreciated, but i think the 1K resistor and the 47uF capacitor should compensate for any ringing, correct?

thebugger

10 years ago

It's just i got a 1k 5W resistor, and it just gets me the right amount of drop, that's why i use it ;)

hurz

10 years ago

The RC 1k 47uF does not damp enough the LC one and wont stop the ringing. Best case it only hide the ringing. Anyway, if you keep anyway from 11Hz resonance (draw current only >>11Hz) then its probably uncritical.

thebugger

10 years ago

Actually I'm not entirely sure that the choke i have is 4H. It only says ДР-2Л and i wasn't able to find any data for it. I determined it mostly by proxy,looking at its size, and i took the 2 in the designation and doubled it because it's a dual choke and I'm using both of the chokes. Is there a way to determine its inductance, and actually if there's any ringing?

hurz

10 years ago

Yes sure, i guess you do not have a function generator by hand, so apply another little AC source/transformer to the coil and measure the current and voltage which represents Z. R you already know and with the geometric addition formula Z^2=R^2+X^2 you can solve for X and with the given frequency of 50Hz you can calculate L with X=2×pi×f×L

thebugger

10 years ago

Okay I'll give it a shot. So i connect it to the transformer, measure the current the voltage, than what's that formula why Z^2? Can't it be just Z? After i know thw reactance, I'll figure it out, just the Z formula.

thebugger

10 years ago

I got exactly 6mA at 50Hz/16.5V. Now please follow my math because I'm not very good at it :D by ohm's law i get R=U/I R=16.5/0.006 R=2750ohm. Now i substract 125ohm from that and get 2625ohm. Using the Reactance formula i get that at 50Hz 2625ohm is 8.356H. Am i correct? I just noticed that the circuit is a little different than the one i posted i am gonna change it to the way it's on the board and wait for an opinion.

thebugger

10 years ago

It turns out there is ringing the way i did it, and the caps are rated 400V so there's a good chance this will blow in my face sometime.

thebugger

10 years ago

I think that the ringing will stop if i increase the 125ohm resistance to 340ohm, and take one of the 47uF caps that are in parallel and put it at the output. Correct?

hurz

10 years ago

Almost correct ;-) the square is important if Z and R are closer. In this case it would be already a good approximation. Cuz Z=2750 is dominating. Anyway to be correct it is X=sqrt(z^2-r^2) = 2747Ohm. L=2747/6.283*50=8.74H

hurz

10 years ago

http://everycircuit.com/circuit/6618833581244416

hurz

10 years ago

And one more unlisted http://everycircuit.com/circuit/4892040637710336

thebugger

10 years ago

Okay let me redo the schematic and tell me your opinion.

thebugger

10 years ago

Okay will try to remember to use the square for most accurate calculation.

thebugger

10 years ago

So the critical dampening resistance will be 430ohm for 8.74H and 47uF? 430-125=305ohm, and i placed 220ohm. I'm not sure i have a 300ohm/1W resistor. Isn't 220ohm close enough?

WTFCircuit

10 years ago

How much phisics

thebugger

10 years ago

Believe me, that's not physics. Try to understand how dark matter reacts to black holes and then we'll speak haha. It's mind boggling :D

thebugger

10 years ago

That's merely engineering ;)

WTFCircuit

10 years ago

Yes, you're right

hurz

10 years ago

430 Ohm would be under damped. 860 is critical damped. >860 is over damped. Anyway, this is only valid for LCR only. In your case input and output has also impact. So give a try.

thebugger

10 years ago

So, bottom line, should i keep it this way or further increase the dampening resistor?

thebugger

10 years ago

How do you determine the dampening factor? Why do i get 550ohms at 100Hz? Isn't critical dampening at 1/10th of the fundamental frequency?

hurz

10 years ago

Ringing is a resonace, check thus http://everycircuit.com/circuit/6618833581244416

thebugger

10 years ago

R=2/sqrt(C/L) is the formula for critical dampening? I've forgotten these formulas since the 9th grade :/

thebugger

10 years ago

I have an 820ohm resistor at 2W, I'm thinking of using. But 820ohm+125ohm from the internal resistance equals an overdampening. Hmm I'll think about how to do it.

thebugger

10 years ago

I can parallelise 820ohm and 10kohm to get 760ohm. 760+125=885ohm which is a little overdampening.

hurz

10 years ago

Does it work?

thebugger

10 years ago

Yes it does. Even with the 220ohm resistor it works normal, with no apparent ringing, and no extreme dampening also. It works good ;)

thebugger

10 years ago

I found out why there isn't any ringing. It turns out that the old radio 📻 I'm using it on has its own filtering capacitor of 200uF that seems to be damping the ringing completely.

hurz

10 years ago

Could you update the schematic and description :-) otherwise its difficult to talk about.

thebugger

10 years ago

Everything's the same. The only difference is that in parallel to the 2x output capacitors there is one more (200uF). I'll add it to the circuit.

thebugger

10 years ago

Actually this is how I'm thinking of rebuilding it.

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