Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Balticnoiseforge on January 04, 2024, 05:32:47 am
-
Iam hellbent on using x3 voltage regulators on a little experimental for fun amp iam building.
A OD3 and x2 OB3 tubes.
But iam finding so much contradictions information on the web, ive drawn up a PSU of how i first thought to use them ( forgot to add a 22uF capacitator between 1n4007 diode and choke at the Voltage regulator part. ).But would basically only using a regulated output to power a EM34 tube while rest of preamp/phase inverter would be after the second choke.
Obviously this is not the best way to design something, but it is fun with old tubes glowing and the PT have quite abit more mA than it needs.
I think this may work, even if iam sure it isnt the best way - but also had idea of simply having the vr tubes outside the psu, simply as a light bulb block - so basically a resistor sized for least amount of current but still lighting them up and have a load for them that wouldnt drain to much.
So i wonder if anyone seen a circuit out there like that? Must have been done before, and better using some mosfet or such to keep the load low etc.
So have anyone seen some circuit online like that which i could try copy?
-
If all you want is to see the cool glow then you can simplify that circuit considerably. All you need is one resistor and the three VR tubes, all connected in series and tapped onto some B+ node, probably just after the choke. The 0B3 is a 90V regulator and the 0D3 is a 150V regulator, so all three in series will regulate at 330V. I would choose a resistor that will limit the current to 10mA. Example, say you are connected to a 400V B+ node. You need to drop 400-330=70V and you want 10mA. Ohms law says R=E/I, so your resistor will be 70/.01=7000Ω and it will dissipate .7W. I would use a 6800Ω/3W resistor.
-
Ah so you would only need a resistor of that value down to the regulators in series? And they would not be needed to connect to a load also but simply grounding them to glow up?
So basically a endpoint of 150+90+90 going nowhere?
I suppose still using bleeder resistor between them would be a good idea, but i dont get the formula, ive seen 100k and 220k used, would any of those be a good choice?
-
No bleeders! All you need is one resistor and the three tubes. Use the example above to calculate resistor size depending on your B+.
-
How come bleeders would be a bad thing? Is it due to dropping the voltage to 330 already and the minimum ignition of the tubes? Or has it to do with something else?
Like increased current waste?
-
Bleeders are simply not needed.
-
Okay, simply read so much different about voltage regulators so had to ask.
But this is last time ill use them simply for glow, used before to regulate screen grid on sweep tubes.
But i thank you for informative answers.
-
Okay, simply read so much different about voltage regulators so had to ask.
But this is last time ill use them simply for glow, used before to regulate screen grid on sweep tubes.
But i thank you for informative answers.
VR tubes are directly analogous to (solid-state) Zener diodes. Both devices are "shunt regulators" and what applies to one, applies to the other. Ok, one caveat - Zeners are polar devices so it matters which way you have them installed, but VR tubes are non-polar and don't care either way.
In either case, a shunt regulator needs to be biased so that it's sinking full required current at idle, with no load - plus a margin of safety per the manufacturer's data.
The extra margin is required so that when the load is sinking most of the current, there is still enough flowing through the reg to keep it operating at its design voltage. If the current drops too low, the reg will fall out of spec.