Tube Rectified Power Supplies

[Sheldon]

BTW, I should have mentioned that the safest way to measure the secondary of the transformer is to feed the primary with a lower AC voltage - let's say 6V. You might also want to include a something like 100k across the secondary. Then multiply the secondary reading by your line/6 (using the exact measured voltage for each). This will give you the unloaded secondary voltage at your actual line voltage.

Sheldon

 

[trobbins]

Psud2 has good help documents. Well worth reading to start your learning curve.

 

[Miles Prower]

I'm sorry if this topic has been covered in another thread. How do I calculate the resistor values in a tube rectified power supply? I have a Hammond 269jx transformer, 500V CT . I'm using a 6x4 rectifier. The unloaded voltage after the 6x4 is approximately 330V. I need to supply a circuit with 295V @ 30 milliamps. The trans is rated 250-0-250 @ 69ma. How do I calculate the resistance needed to drop the 330V to 295V?

What kind of ripple filter? CLC or CRC?

That 330V is the unloaded output. You will see that drop under load due to the increased forward voltage across each section of the 6X4. Furthermore, that's just 35V over the design nominal 295. Remember: transistors have ratings; vacuum tubes have suggestions. Going 35V (and you'll lose some under loaded conditions) is nothing. Nothing will poof here, unlike the more sensitive solid state.

You will probably find that your actual voltage will be somewhat under the design nominal value here. If I_surge is ~ 140mA/plate, you're already losing the excess to forward drop. There will be added losses due to PTX winding resistance, drops across choke R_DC, voltage averaging at the reservoir capacitor. You might find your actual voltage is under the design nominal 295V if you do nothing at all.

 

[TonyTecson]

^yes, the dc resistances of the transformer secondary referred to primary will ensure that the unloaded B+ of 330v will drop once current starts to get drawn....

 

[TonyTecson]

OK John,
You state "Ohm's Law"....How about expanding that a little? How do you use Ohm's law if you know the starting voltage of 330V, and know that 295V is required? I know my question may seem obvious to others, but I am new at building tube circuits. In fact this is my very first hands on prototype build. I'm not building anything special, just a simple tube rectified power supply. Eventually when I get through the learning curve, I will use the power supply in a preamp. As far as using PSUD2, its not all that straight forward for me.
If you could please show me the actual calculation it would be a great help in me learning how to calculate how much voltage I would wind up with after adding the caps and resistors to the circuit. Thanks in advance, PK

if you are merely building and not designing, computations by ohm's law are hardly of use to you, i say just do it and learn from it..

 

[crazyfrog]

My life changed since I use PSUD2! 😀 Very useful. Especially if you use tube rectifier.

 

[TonyTecson]

yes, that software lets you see the voltage ramping up....
here is a good link about tube power supplies....powersupplies