diytube.com

Hey Guys,

How does this circuit look? Any technical scrutiny would be much appreciated.

http://www.diyparadiso.com/psekt881.htm

Thanks,

Min

Ability to go class A2, but other than that, somewhat common.

A trick I'd pull on that, like putting the secondary inline with the cathodes so the DC unsaturates the iron a tad and gives some local cathode feedback

KT88 isn't given to a low output impedance, even in triode, without NFB of some sort.

Cheers!

Hybrid SS FW bridge/tube FW rectifier for slower start up and better reverse voltage blocking than a pure SS bridge. DC on the filaments. Lundahl iron is big coin. For stereo: 2 interstages, 2 outputs and 4 chokes (the chokes are not specified as Lundahl however) are needed.

In audiodesign's SE, he uses the same Lundahl interstage, but he goes volt amp -> volt amp -> interstage with a 6sn7, instead of the parallelish 6sl7 -> interstage as in diyparadiso.



You could go cheaper and just parallel a KT88 in the schematic (or a similar one) below:



If your intent with the PSE is go into A2, a chip amp -> Electra-Print interstage for the driver would be more reliable and cheaper than the 6sl7 -> Lundahl interstage. I do not know how may clean Watts the 6sl7 -> interstage combo can put out, but a chip amp -> interstage can do around 10W, perfect for reliable A2.

Thanks, gents! How does the cascaded 6sn7 compare to the paralleled 6sl7? Will the latter have enough drive for the KT88s through the IT?

The voltage gain (and mu) in paralleled triode sections will be the same as a single section (provided the plate and cathode resistors are dropped by half as in a single section and the grids are strapped), so cascaded triodes for this circuit should supply more voltage swing.

http://tubes.nekhbet.com/math.shtml#para

You can't go wrong with this design, but it seems a bit pricey for PSE KT88s. The designer may not have needed that much swing to drive 2 KT88s. Maybe you could email him to ask why this set up?

I am actually building a pair of monoblocks for someone else and he is pretty adamant about using Lundahls and wants ITs in the circuit. Cost is no object here since he is paying. I have built amps with the 6SL7 in SRPP configuration with good success as well as paralleled 6SL7 driving a single 807 through a coupling cap but I have never ventured into a paralleled 6SL7 driving a pair of KT88s through an IT before. That cascaded 6sn7 looks pretty good. It's my favorite tube too. I might just go with that setup instead. Thank for the suggestion!

Min

Do you have a link to the PS schematic for the 6sn7 cascade driven circuit? Thanks. Min