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KaffiMann 6th October 2009 08:50 AM

KT88 blocks? With E80CC + 6922 driver?

I have no idea where I should start.
I have an amplifier I want to kill (reads; salvage parts from). So I have some kt88`s, and a bunch of 6922 + one pair of E80CC that match very well together. The transformers are good enough, so I will use them too.

I looked around for something to base the project on (I have no clue about tubes, been soldering a lot, but not much on tube gear). I found this PCB in some thread here:

And I have been looking at this "Einstein" solution for a while:

Again, I have no real knowledge about tubes, the last link is evolved around an EL84 design, and it`s also SE, is it possible to make something like this with KT88 tubes, and with PP/UL?

The amp I have now annoys me with noise, I can barely hear it, but it`s enough to know it`s there, since I am planning new 103 db/w speakers, i have to do something about it. I have some brand new caps in there i will also salvage, but the rest is going to the bin.

So to keep it short, I want KT88 ultra linear with E80CC + 6922 driver stage, with NO NOISE.


SY 6th October 2009 10:39 AM

Suggestion: input/driver tubes are cheap. Instead of deciding what the input/driver tubes have to be, then trying to design a circuit around them, why not design the circuit and then decide what the tubes have to be?

You might check the schematics at Allen Wright's site- he uses a hybrid cascode with ECC88 (6922 is a substitute), which is a fine driver stage.

KaffiMann 6th October 2009 08:51 PM

I do see your point.

I realize it's possible to use alot of different things for the driver stage, and I understand that I may have formulated things better.

The main thing is really the KT88 UL thing.
Is it even remotely possible, to combine a good KT88 design with this:


I can figure out the other tubes later, but it would be really nice to be able to use the ones I have right now.

SY 6th October 2009 09:13 PM

That's probably not your best starting point. A PP design will be intrinsically quieter because of the common mode cancellation. So you really don't need to do anything exotic in the design like Broskie does here for the SE circuit. I'd still recommend a more conventional PP circuit, but pay close attention to grounding and use a good quality regulator. That should satisfy your need for quiet operation and excellent dynamics. Allen Wright's PP1C amp could certainly accommodate KT88 in UL.

New Mandated FTC Disclosure: Broskie has given me circuit boards. I have given him transformers. Earl Grey has provided the tea I'm drinking. Allen Wright bought me a beer and autographed his book.

boywonder 6th October 2009 10:43 PM

Kaffi: Are your output transformers single ended or PP?

SHiFTY 6th October 2009 11:18 PM

What amp are you starting with? Why not rebuild it if it is in working condition? Perhaps if you have some pictures and / or a schematic that would help.

Allen Wright 6th October 2009 11:33 PM

I don't use hybrid cascode front ends in my poweramps - they are all tube.

I do use hybrid cascodes in my phono sections of my preamps, but that's kinda different.

Regards, Allen (Vacuum State)

SY 6th October 2009 11:36 PM

I stand corrected.

I used both a ECC88 cascode diff amp and a hybrid cascode diff amp with a 2N5566 on the bottom in some PP amps and found that both ways worked very well.

KaffiMann 7th October 2009 06:35 AM

boywonder: the transformers are for PP.

SHiFTY: It's a Music Angel XDSE-800 MK2 or MK3, not really sure. It was bought as an MK2, but it there are some changes in it that makes it seem like an MK3.

I've changed most big caps, most of the wiring, and put in faster diodes. I am still not satisfied with the noise floor. And it also seems to oscillate just a tiny bit (was far worse to begin with). It's a lot better than what i thought i would get originally though.

Was thinking of just making mono blocks with the best parts, making it all point to point, and make the psu external.

boywonder 7th October 2009 10:49 PM


Originally Posted by KaffiMann (
boywonder: the transformers are for PP.

Was thinking of just making mono blocks with the best parts, making it all point to point, and make the psu external.

Since your OT's are PP, looks like SE is out of the question. (your schema posted above is SE, that's why I was asking about your transformers)

Have you checked out the Mono Bill? It's PP KT88 UL

There is also a version II of the Mono Bill:

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