Power supply for tube preamp

[rankot]

I am building an Alembic F2a preamp, and I am just curious if using fast switching rectifier diodes like BA157 for power supply will make any difference is sound compared to 1N4007?

[tubegeek]

It's POSSIBLE they might put a smaller turn on/off spike back into the power supply, couldn't hurt. I use fast/soft diodes on my SS power supplies.

[amptramp]

Normal 1N4007 diodes exhibit a reverse current that sweeps all the charge carriers out of the junction and this pulse can be anywhere from 27 to 35 MHz.  Since I restore an FM tuners and the third harmonic is in the 88 - 108 MHz FM band, this is a prime consideration in a lot of my builds.  If you are using it where there is an RF link from the player to the amplifier, you could get some interference.  Tube rectifiers do not have this problem.

There is another thing you can do: add a series R-C network across the B+ secondary winding (and the size of the R means the secondary winding sometimes only needs a C).  The idea here is that as the secondary voltage goes from +0.7 volt to -0.7 volt, the diodes are not conducting and the secondary is "released" from the circuitry and can ring on its own, usually at something like 100 KHz.

Some people also add grommets under the transformer mounts to keep the transformer from inducing current in the chassis.  There may still be a need to ground the core but this can be done with a wire or possibly through a resistor.  This is even more important if you use a fullwave doubler where capacitive coupling to the core can cause 60 Hz hum.  I only have a schematic for the F2b which has a halfwave doubler, so if it is different from the F2a, you may feel free to ignore some of this advice or try it - it may make a difference.

[rankot]

I have found this https://diyaudioheaven.wordpress.com/tutorials/power-supplies/snubbering/ interesting article on the topic, so I will try to add RC snubber filter. But my main question is still - is there any difference in DC voltage stability regarding different diode choice?

[rankot]

And actually my schematic is also for F2b, but with 220V mains, so it uses rectifier instead of doubler.

[BubbaFet]

Read this artical. . .

http://www.valvewizard.co.uk/smoothing.html

Personally, for that preamp, I think the capacitor charging currents are low enough where choice of diode is not something to be overly concerned about. Rather, focus on the values of your filtering capacitors.