Say a fella wants to build an SET monoblock based on the 300B..

Charles,
I played with the AC filament heating for a while, then decided to add the DC heating as I was using sensitive speakers. That was a good move,  reducing the noise floor substantially. At the time I had 100 dB Zu Audio Soul Superfly speakers with a Dynaudio Sub 6 to handle the low end. Right now I am awaiting shipment of a set of Jager speakers from Bottlehead to build and try, hopefully without a sub. I am using a BeePre 2 as a preamp, and have a Rega P6 turntable with a Bottlehead Eros 2 tube phono preamp as my source for analog. Call me a DIY devotee a Bottlehead fanboy! 
Scott

Hi Scott,
I’ve followed Bottlehead’s Paul Joppa on Audio Asylum (SET Topic)  for years and have always been impressed with his electrical engineering knowledge as it relates to audio products. Very curious how the Jager will compare to your Zu Audio Soul Superfly.

Some purists believe that AC filament heating is a bit more natural but many builders disagree and say well implemented DC heating is as good sounding if not better.
Charles

O.P., since you mention you're planning on building your speakers, are you inclined to scratch build your amplifier?

If so, consider this (scroll to page 22): http://www.jumpjet.info/Pioneering-Wireless/eMagazines/VTV/VTV05.pdf 

Eric Barbour's SV811-10 amplifier might look simple, but it is surprisingly quiet and has a great sound stage.  I've built 3 pair of them and have a pair still as backup amplifiers for my Elekit 300B amplifier.

I found the SV572-10 had a nicer presence, smooth and pleasant.  The SV572 triode is quite rugged.  It would take a catastrophic failure of the stage coupling capacitor or grid resistor to drive the 572 into hyper conduction.

SV572 data sheet.

https://frank.pocnet.net/sheets/164/s/SV572-160.pdf

Beware!  If you do build this amplifier, don't get the high gain (µ=160), SV572, you'll be sorry!  Stick with the lower gain µ=10 and enjoy.

Eric gave no parts list as he assumed the builder was capable of finding all the parts necessary.  The parts are indeed still available, just not the PCB ladened Cornell-Dubilier 121 series electrolytics. 

I've upgraded the output transformer to Lundahl (giant leap forward!), replaced the stage coupling capacitor with Jupiter oil/wax type (another notch forward) and the input stage cathode bypass capacitor with an organic polymer type.

6EM7 tubes are still widely available and fairly cheap.  You want a "black plate" RCA, there are lots of them around.

I used an ugly "potato masher" 5R4WGB (Cetron) as Eric shows in the article.  These are also readily available from many sources.

There are some updated rectifiers (SiC) that can be used in the 811/572 filament supply that give even quieter performance.  Although not necessary, I did add a DC supply to the filament of the 6EM7.

This will definitely give you an excuse to buy a set of Greenlee punches to make nice, round holes in your chassis.  (versus something that looks like a rat gnawed it out)


Happy listening