Tube regulator advice

[sumotan]

Hi Guys
Would appreciate some advice. The schematics are for a 300-0-300 ac input with output voltage being adjustable from around 250-320v . With a 250-250 ac input, what changes or do I need to make any on this circuit in order for v-out adjustment of 200-250v

Thank you

 

[jan.didden]

The principle is that the potmeter wiper sits at the same voltage as the zener reference on the other tube grid (150V).

So when you move the wiper, that '150V point' moves up and down the string R6, pot, R7. So if you can't turn it down enough (wiper max up) just decrease R6 (or increase R7) to move the regulation range up or down.

For instance, when you make R6 zero, and turn the wiper all the way up, the output voltage is 150V...

Jan

 

[sumotan]

Thank you kindly Jan

 

[jan.didden]

One thing I forgot: you can't turn Vout all the way down to 150V because there needs to be some minimum anode-to-grid voltage for the tube to work, but I hope you get the idea.

If you still need to go lower you can always replace the 150V zener by a 100V part, and all your outputs go 50V lower.

Jan

 

[sumotan]

Thank you again Jan. Btw I would like to replace R2 with a 20H choke but Im wondering why C2 is of such high value. What’s your thought on this Jan ?

 

[jan.didden]

The RC gives a big attenuation of ripple, but you pay: there's more voltage drop across R2 than you think!


If you want to play with it, download PSUDII which is a little app that lets you set the rectifier and RC values and look at the result in terms of raw voltage and ripple for a specific load. Quite insightful.

Jan

 

[Ketje]

C1 has a limited value caused by the tube rectifier, so they placed a bigger value after a current limiting resistor.
It is that big to prevent the voltage to drop to low between charging pulses.With a voltage to low the pass tube doesn't function anymore.
To answer you question on other voltages, if you keep the 50k potmeter then R7=200k and R4=83,3333.... take 82k
Mona

 

[sumotan]

Thank you Jan & Ketje

 

[jazbo8]

Thread moved to Power Supplies.

 

[bluerooster]

One thing I forgot: you can't turn Vout all the way down to 150V because there needs to be some minimum anode-to-grid voltage for the tube to work, but I hope you get the idea.

If you still need to go lower you can always replace the 150V zener by a 100V part, and all your outputs go 50V lower.

Jan

2 or more zeners with a switch.