Power Supply

[stephenl]

A plate and screen supply is a common element we all use.

I've used this several times. SiC Schottky diode rectification and a capacitor multiplier make for a great clean power supply. Not too stiff, just very low ripple. It also takes advantage of high quality, compact snap in elytics as well.

I can't take credit for the design. It's elements of other people's work. Merlin discusses cap multipliers in his PS book, I added the SiC rectifiers. The sag resistors and snubber caps are from John Broskie - caps probably aren't necessary with the Schottky diodes since there's no reverse recovery.

I've never designed a PCB, but I thought I might try to take this schematic and put it into KiCad.

Fixed errors and ran simulation:

PowerSupply08252018.pdf

Plate Supply Trace.pdf

[stephenl]

I'm slowly teaching myself KiCad.

Anyone see any mistakes so far?

KiCad Power Supply.jpg

[pompeiisneaks]

Hi, I was just wondering if anyone can tell me what current and polarity the power supply for the PX5D uses. The information should be on the back of the plug if anyone has it. I cant find this information anywhere.

I have no idea what the PX5D is. could you specify more detail? Is it a specific PCB? All Google gives me is a power supply for korg Pandora PX5D.

~Phil

[Aurora]

That circuit cannot work.. you need a voltage divider to ground to set the gate voltage.... Why resistors in series with the diodes??? If used they must be very low value....

[DimenBrun]

I'm wondering about the load. You're showing a 13.8k resistor in the .pdf, so at 400V that would be ~ 29ma. What power amp is this for? Idling at 29ma, a single pentode?

[LightningPhil]

That circuit cannot work.. you need a voltage divider to ground to set the gate voltage.... Why resistors in series with the diodes??? If used they must be very low value....

Yep, also wondering what the circuit is for.

But resistors in series with diodes can be useful, makes the on to off transition a little softer and can dampen noise coming from the TX. Quite right, they have to be small unless you're aiming for a current source (handy for sag).

[stephenl]

The series resistors are 10ohm, 1watt or so - just to emulate some sag if you wish and can be omitted. The FET circuit is an active filter to reduce ripple - cap multiplier. The transistor after it is for current limiting/soft turn on for B+.

[Colossal]

Steve,

I remember how good a KT88 sounded running in SE/UL with a cap multiplied power supply. Very tight!

[stephenl]

If I remember correctly, you lose about 20vdc across the filter.

[LightningPhil]

It might be a silly question then...

Why put a cap multiplier after sag resistors. Would that not make the time constant a wee bit too long?

[stephenl]

The cap multiplier's primary function is to filter out power supply noise / ripple.
It's not a replacement for an inductor - like a gyrator. Sag is the power supply's reaction to load changes.
The cap multiplier does a great job of cleaning up B+ without having a big effect on sag. I've used this type of supply on several amps and it really lowers the noise floor a lot.
I didn't include the sag resistors (transformer's impedence is enough for me) or the caps around the diodes (I used SiC Schottky rectifier diodes, little reverse recovery - pretty quiet by themselves.) I just added them in case I wanted to try them out....

As Colossal noted above, SE and UL amps benefit from really clean power supplies even more so.