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Old 5th November 2012, 03:42 PM   #1
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Default Push-pull implemented with KT88

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
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Old 5th November 2012, 04:00 PM   #2
SandyG is offline SandyG  United States
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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
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Old 5th November 2012, 08:30 PM   #3
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I have had a look at that, seems quite interesting

www.triodedick.com/pdf_files_td/Bill_En.pdf
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Old 5th November 2012, 09:34 PM   #4
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by regiregi22 View Post
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
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Old 6th November 2012, 03:01 PM   #5
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In addition to the Bill/Mono Bill, here are a few more:

Mullard 5-20 topology with PP KT88's:

"Mullard 5-20 KT88 PP blocks!

Mullard 5-20 topology with MOSFET followers:

OPUS 5.0 A Modern Mullard

Differential front end with MOSFET followers:

6L6GC AB2 Amp
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Old 15th November 2012, 07:08 PM   #6
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Quote:
Originally Posted by tinitus View Post
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?
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Old 15th November 2012, 07:39 PM   #7
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by regiregi22 View Post
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
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Old 15th November 2012, 08:32 PM   #8
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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
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Old 15th November 2012, 09:25 PM   #9
tinitus is offline tinitus  Europe
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monobill 2 schematic shows 5K6
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Old 15th November 2012, 09:31 PM   #10
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OK! Thanks!
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