Simple Variable Tube Power Supply

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Sal Brisindi

Sal Brisindi

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Joined 2006
tuberadios.com
#1
If you are interested building a tube based high voltage adjustable power supply, I just scanned and uploaded to my website an article from January 1963 Popular Electronics. Its a simple power supply to build using just 1 6L6GC or other popular audio tubes with an output from 60 to 300 vdc. Its not regulated but functional for you experimenters.

http://www.tuberadios.com/temp/powersupply1.jpg
http://www.tuberadios.com/temp/powersupply2.jpg

Regards,
Sal Brisindi
 

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#5
Sal Brisindi said:
There is one thing that puzzles me, you will notice the center tap of the transformer feeding the filament to the 6L6 tube is connected to the B+, very strange. I would think it would be connected to the ground.
Click to expand...

It's connected that way so that the insulation between the heater and cathode doesn't break down.


And as I mentioned before, its not regulated.
Click to expand...

More like an active decoupler, actually.
 
#7
Maybe a stupid question, but, anyway, I'll throw it in, as I may have a use for it, in case it works. Can I substitute the tube for a well heatsinked mosfet (IRF820)? A 1M pot between B+ and ground, wiper to gate, drain to B+ and source as output?

Erik
 
#9
ErikdeBest said:
Maybe a stupid question, but, anyway, I'll throw it in, as I may have a use for it, in case it works. Can I substitute the tube for a well heatsinked mosfet (IRF820)? A 1M pot between B+ and ground, wiper to gate, drain to B+ and source as output?

Erik
Click to expand...

You asked for it, here it is. A solid state mosfet 0-300 vdc variable power supply with a minimum of parts. I wanted to build this supply but never got around to it.

http://www.geocities.com/tjacodesign/300vsup/300vsup.html

Regards,
Sal Brisindi
 
#12
This would not be a good circuit for a regulator for a piece of audio equipment. Line/ripple rejection borders on nil. Since you just need a fixed supply, for about the same parts count you can build a simple series feedback regulator. Use the MOSFET as the pass device (remember a gate-stopper resistor) and an NPN as an error amp.
 
#14
Reasonably. But the reference voltage in this circuit is the ripply, noisy, bouncy raw supply. The source impedance of the FET, open loop, will be pretty mediocre. Even at full load current, the gm of the FET is likely to be on the order of 0.1A/V at best.
 
#15
Here is an interesting schematic. Two 6P3S (6L6) pentodes, in triode conection, are working as controlled rectifiers with surprising performance (40V to 380V @ 180mA).
Maybe somebody is so nice to translate the text.
 

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#16
#17
Sal Brisindi said:
If you are interested building a tube based high voltage adjustable power supply, I just scanned and uploaded to my website an article from January 1963 Popular Electronics. Its a simple power supply to build using just 1 6L6GC or other popular audio tubes with an output from 60 to 300 vdc. Its not regulated but functional for you experimenters.

http://www.tuberadios.com/temp/powersupply1.jpg
http://www.tuberadios.com/temp/powersupply2.jpg

Regards,
Sal Brisindi
Click to expand...

I have to revive his thread as I have a question. I would like to double the current handling on this design. Is it possible if I'll parallel connect the 1619 tubes and lower the cathode resistor to 50K (from 100K) but double the wattage?

Like Sal, I don't want a regulated B+ just a variable voltage functionality.

Thanks!
 
#18
R4 just acts as a bleeder (safety discharge) resistor for the C2 output cap and as a minimum current load for the inductor L1. But its effect is variable due to the voltage dropping in the tube. Output V will jump appreciably at low current since the V reference for R1 will change significantly. (see a tube power supply design manual for this) This is a pretty shaky design without a real Voltage reference.

R1 determines the grid voltage, and has full range variation from 0V to B+. The output V is roughly that R1 V setting. Needs gm(total) x Output current for grid drive. (not counting triode plate feedback and B+ and Watt diss. limits) The rectifier (could be SS) and HV xfmr and L1 inductor need to be rated for the current and Watts. (xfmr at least 1.1X the output current)

The 1619 lists at only 15 Watt max dissipation and 50 mA max DC current (1/2 a 6L6GC). Using two tubes will double that if they share the current equally. You will want to check the current for each tube to see if they track. (essentially you need matched tubes)

Using a single TV Sweep tube like a 6DQ5 or 6CB5A would be easier. A Heat-sinked HV Mosfet even easier yet.

Much better regulated designs:

http://www.diyaudio.com/forums/tubes-valves/118581-high-voltage-bench-power-supply.html

http://www.diyaudio.com/forums/tubes-valves/287090-bench-supply.html
 
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#19
smoking-amp said:
R4 just acts as a bleeder (safety discharge) resistor for the C2 output cap and as a minimum current load for the inductor L1. But its effect is variable due to the voltage dropping in the tube. Output V will jump appreciably at low current since the V reference for R1 will change significantly. (see a tube power supply design manual for this) This is a pretty shaky design without a real Voltage reference.

R1 determines the grid voltage, and has full range variation from 0V to B+. The output V is roughly that R1 V setting. Needs gm(total) x Output current for grid drive. (not counting triode plate feedback and B+ and Watt diss. limits) The rectifier (could be SS) and HV xfmr and L1 inductor need to be rated for the current and Watts. (xfmr at least 1.1X the output current)

The 1619 lists at only 15 Watt max dissipation and 50 mA max DC current (1/2 a 6L6GC). Using two tubes will double that if they share the current equally. You will want to check the current for each tube to see if they track. (essentially you need matched tubes)

Using a single TV Sweep tube like a 6DQ5 or 6CB5A would be easier. A Heat-sinked HV Mosfet even easier yet.

Much better regulated designs:

http://www.diyaudio.com/forums/tubes-valves/118581-high-voltage-bench-power-supply.html

http://www.diyaudio.com/forums/tubes-valves/287090-bench-supply.html
Click to expand...

Thanks Smoking-Amp for a very detailed explanation.

Good thing you've mentioned the use of TV tubes which our country still has a few. However, I could not find 6DQ5 or 6CB5A as you have suggested. Will a 6LQ6 do the job? it could dissipate 30Watts on the plate as well.

I was also considering the use of IRF840 with a string of Zener diodes(on a rotary switch) connected to the GATE.
 
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