Simple PSU for tube microphone - need some help :)

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ln76d

Well-known member
Joined
Aug 11, 2012
Messages
2,486
Location
Gallifrey
Hi Guys,

i need to build simple PSU for microphone with one 6028/408a tube.
Filament: 20V/50mA
Plate: 105V
I have transformer with secondaries:
200V/40mA
60V/70mA
10V/200mA

For plate voltage, my idea is to connect 60V and 200V windings in parallel - lowering voltage to 130V and get higher current supply.
For heaters  voltage, my idea is to use voltage doubler.
Schematic attached.
Could someone check that for me?
Is it filtering enough?
Is this configuration of voltage doubler would be ok for current load?
 

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What do you mean "connect 60V and 200V windings in parallel "?
You want to compete with electroBOOM?
NO WAY!
You would get more current IN the transformer and blow it.

Now regarding teh voltage doubler, you need to increase C1 &C2 by a factor 10 at least.
 
Thanks!

Now i see how stupid idea it was :D
Also current consumption should be less than 1mA...
eh...  I'm tired and not clearly thinking.

I guess, that in both cases voltage doubler would be best option.
I never before used voltage doubler.
Is there any formula to calculate C1 and C2 values?
Doesn't double 1000uF rise current draw?
 
ln76d said:
Thanks!

Now i see how stupid idea it was :D
Also current consumption should be less than 1mA...
eh...  I'm tired and not clearly thinking.

I guess, that in both cases voltage doubler would be best option.
I never before used voltage doubler.
Is there any formula to calculate C1 and C2 values?
Doesn't double 1000uF rise current draw?
For calculations, you must consider C1 & C2 are in series and it's single-wave rectification

dV=.I.dt/C
with dt=1/60 for US and 1/50 for the rest of the world and C being 1/2 of C1 (or C2).
And after that you must calaculate the ripple attenuation provided by the filter, but I see you have a simulation package.
The 6028 is indirect heat so noise on heater voltage is not a major issue, as long as there are no sharp spikes that could propagate.
In fact I've been pessimistic; it turns out that 2x100uF could give an acceptable result, but I would use a higher value because it gives nasty spikes at the rectifier's output.
A good compromise would be using 4x470uF caps and 2 x68ohms res.
 
ln76d said:
For plate voltage, my idea is to connect 60V and 200V windings in parallel - lowering voltage to 130V and get higher current supply.

You want to say  "to connect 60V and 200V windings" in anti-serial - "lowering voltage to 130V".
Connecting two secondaries that way it would work. The maximum current you can get is limited to lower value of both.
 
Hi moamps!
Thanks for the input ;)

What's the "anti-serial"?
Are we talking about the same connection?
I had in mind something like in  attachment.
After abbey road d enfer reply i found only one source that confirmed it is stupid idea.
I know that two windings with the same voltage can be connected (let say) in parallel.
I don't need higher current but only lower voltage.
 

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ln76d said:
Hi moamps!
Thanks for the input ;)

What's the "anti-serial"?
It means the windings are connected in series but one is out-of-phase respective to the other, so voltages substract instead of adding.
I had in mind something like in  attachment.
In your example, the windings fight each other, dissipating a lot of heat (you may verify that by probing current across the windings and across the voltage source).
 
Ahh!!!

Now i see :D :D :D

Multum thanks Guys!

Something like this, right?

140V make sense :)
 

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abbey road d enfer said:
You want to compete with electroBOOM?
NO WAY!

Ha, that was the best thing I saw all day yesterday.  So much that I've ripped your phrase off to title my following drawing.


For some reason I felt the need to made some diagrams using voltage sources to show the "Anti-serial" connection being discussed and the parallel electroboom drawn out as two sources connected together through their DCRs.  You can see in that one that you will get an intermediate voltage at the middle, as you simulated, but that happens by driving absurd amounts of current from the 200V side to the 60V side.  You're basically shorting the 140V difference  through the windings of the transformer, which are not going to like that one bit.

(Note  that the 60V on the left side is wired with positive at the bottom)
 

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