Push-pull implemented with KT88

[regiregi22]

Hello,
I am planning to build a push-pull KT88 based amplifier. I would like to make it operation type selectable by using a switch, so I can operate the tubes at Triode, Ultralineal or Pentode, depending on my PWR needs, and mostly for audio comparisons purposes. Fixed bias provided by extra turn on xfmr.

I could use a different tube rather than KT88, but what the h*ck, it's among the best tubes in its power rating. I haven seen some pcb boards (like pmillet's) that come very handy if testing and breadboarding, but it will be a final assembly, not an amplifier to experiment, so I will P2P it.

What is a common, high-end, not very complex schematic to use? I don't really care if it is a complex desing, but life's such, that simpler ones use to be the better ones. I don't really need to be able to select between triode, UL and pentode, that's something I am able to put in by myself 🙂

If you were about to build ONE, with these requirements, what proved schematic would you implement?

Thank you and best regards,
Regi

 

[SandyG]

Look to the Dynaco schematics with modifications to the driver board, a ton of them floating around, for the Monoblock's look for the MKIII amps and for a stereo version the ST70. Lots of transformers from several sources and I think just an update to the driver and you will have a simple good sounding amp.

Sandy

 

[regiregi22]

I have had a look at that, seems quite interesting

www.triodedick.com/pdf_files_td/Bill_En.pdf

 

[tinitus]

I have had a look at that, seems quite interesting

www.triodedick.com/pdf_files_td/Bill_En.pdf

Mono Bill or Mono Bill II are later KT88 designs

don't know if its true, but I got the impression that the KT88 quality could be an issue

 

[boywonder]

In addition to the Bill/Mono Bill, here are a few more:

Mullard 5-20 topology with PP KT88's:

http://www.diyaudio.com/forums/tubes-valves/156699-mullard-5-20-kt88-pp-blocks.html

Mullard 5-20 topology with MOSFET followers:

http://www.diyaudio.com/forums/tubes-valves/161702-opus-5-0-modern-mullard.html

Differential front end with MOSFET followers:

http://www.diyaudio.com/forums/tubes-valves/133034-6l6gc-ab2-amp.html

 

[regiregi22]

Mono Bill or Mono Bill II are later KT88 designs

don't know if its true, but I got the impression that the KT88 quality could be an issue

Why? Ain't KT88 good enough performers?

 

[tinitus]

Why? Ain't KT88 good enough performers?

ahh, yeah, I guess they are ok
I meant, a KT88 may not be all good just because it says KT88 on the bottle 😉
hope its ok to call it a good alround performer and 'middle of the road', so to speak

 

[regiregi22]

I think I am going with Triode Dick's, but I can't find anything related to output transformer impedance, power and other characteristics on its website. Do you know what is used in the original design or should I just calculate it?

Link to the translated website:
Bill Part 7

 

[tinitus]

monobill 2 schematic shows 5K6

 

[regiregi22]

OK! Thanks!

 

[crispycircuit]

No feedback ?

This type of circuit usually benefits from some low feedback. The feedback will also affect the gain of the amps input/driver stage. Does anybody else think feedback would help on the amp?? What's the sensitivity or the voltage needed to drive the amp to full power?

 

[scott17]

Have you looked into this design?

PP2012 - KT88 Hi-End Push Pull Amplifier

 

[regiregi22]

Have you looked into this design?

PP2012 - KT88 Hi-End Push Pull Amplifier

mmmm another very interesting option, will look about it. thanks!