PSE KT88

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Hey Guys,

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

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

Thanks,

Min

[Geek]

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!

[kheper]

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.

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

[kheper]

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?

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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

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

[kheper]

http://www.audiodesignguide.com/my/se.html