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Old 10th March 2006, 10:20 AM   #1
Lucas_G is offline Lucas_G  Netherlands
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Default Please advice on KT88 Push Pull

Dear Tube experts,

After modifying a Dynavox 70 with better tubes and caps, I am so convinced by the performance of a push pull tube amp (my speakers are 89 db at 4 Ohm) that I would like to build such an amp myself with KT88 instead of El34.

I have been looking around and found these two designs:

http://www.triodedick.com/monobill_deel_1.htm
scheme is here:
http://www.triodedick.com/monobill/m...versterker.GIF
Psu is here:
http://www.triodedick.com/monobill/m...%20voeding.GIF
(This design by Triodedick has got much laud by dutch diy folks).

and another design for 2 or 4 KT88:
http://jastrid.xs4all.nl/Dalojan/KT88_PP.html
scheme: http://jastrid.xs4all.nl/Dalojan/Schema_KT88PP.html
psu: http://jastrid.xs4all.nl/Dalojan/Sch...ng_KT88PP.html
scheme 4 KT88: http://jastrid.xs4all.nl/Dalojan/Schema_4_KT88PP.html
psu 4 KT88: http://jastrid.xs4all.nl/Dalojan/Sch..._4_KT88PP.html

The latter provides a balanced entry. Could one also modify the other amps with 2 KT88s for balanced operation?

Which one seems better on paper?

I am a newbie with regards to tubeamps.
To me, a good reproduction of space/reverb in a recording is paramount. And of course the ability to drive my speakers. Others have warned me that a SET would have difficulty here.

Any suggestion or hint is most welcome!

Lucas
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Old 10th March 2006, 10:49 AM   #2
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Hi Lucas

All schematichs are pretty alike, I didn't read the story behind the Dalojan, but guess it is a kind of copy of the bill amp from triodedick.

All amplifiers use a LTP as phase splitter/driver, implying that all can be driven by a balanced signal. Just copy/paste everything that comes in front of the ECC99 in the schematic of the Dalojan with 4 KT88's to the Bill and the 2 KT88 dalojan.

The use of 4 output tubes instead of 2 just delivers more power or a reduced output impedance. I would go for the 2 KT88 / channel. This will give enough power for your speakers. I can't comment on the use of the CCS for the KT88's in the Dalojan. Maybe you could at a first moment just build the Bill, and when you get more confident about this CCS stuff you give it a try for the KT88's. Nice thing here is that you don't have to rebuild the whole output stage!
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Old 10th March 2006, 01:53 PM   #3
Lucas_G is offline Lucas_G  Netherlands
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Quote:
Originally posted by ErikdeBest
Hi Lucas

All schematichs are pretty alike, I didn't read the story behind the Dalojan, but guess it is a kind of copy of the bill amp from triodedick.

All amplifiers use a LTP as phase splitter/driver, implying that all can be driven by a balanced signal. Just copy/paste everything that comes in front of the ECC99 in the schematic of the Dalojan with 4 KT88's to the Bill and the 2 KT88 dalojan.

The use of 4 output tubes instead of 2 just delivers more power or a reduced output impedance. I would go for the 2 KT88 / channel. This will give enough power for your speakers. I can't comment on the use of the CCS for the KT88's in the Dalojan. Maybe you could at a first moment just build the Bill, and when you get more confident about this CCS stuff you give it a try for the KT88's. Nice thing here is that you don't have to rebuild the whole output stage!
Hi Erik,

Thanks for your comments.
So starting with the monobills seems a good idea...
Any thoughts on further upgrades?
Is the PSU as described there stable and clean enough?

Any other recommendations from other countries?

Regards,

Lucas
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Old 10th March 2006, 02:01 PM   #4
beamnet is offline beamnet  Netherlands
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I've been fiddling with these a lot. Very ease first project, can't go wrong there. I ended up with different tubes, but essentially it's the same.

Triodeick is known to be in the grey area between engineering and high-ending. But this one's rather well calculated. The coupling caps to the output stage are a bit lean. I greatly preferred 0,47 uF there.

In my case, the amp sounded better with 6n6p tubes instead of ecc99, but that is grossly subjective and dependent on music choice.

If you want, i have some really cool input tubes for you that can substitute the 6sn7. They look waaaay cooler and sound heaps better than any 6sn7 tube which is completely hyped up at tha moment. they are single triodes thoug, so they are ideal for monoblocks.
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Old 10th March 2006, 02:13 PM   #5
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Hi Lucas

I see you are (at least a bit) like me, thinking about upgrades even before building the first version. If you recognize yourself in this position: I would go with the monobill, but with separated chassis for the PS and for the amplifier itself. This way you get a total of four chassis. Buy four (secondhand) 19 inch enclosures and put the prototypes build on breadboards in there. Cosmetics won't be that good, but you've got great freedom and space to change circuits to your taste!

Erik
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Old 10th March 2006, 02:41 PM   #6
beamnet is offline beamnet  Netherlands
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To my taste, the recommended input xfrmr from ae is too small. I am researching inrusch current limiting stuff, beacause it has a hard time filling th huge caps and providing current for the cold fillaments.

Bas
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Old 19th May 2006, 05:37 PM   #7
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Default Re: Please advice on KT88 Push Pull

Quote:
Originally posted by Lucas_G
Dear Tube experts,

After modifying a Dynavox 70 with better tubes and caps, I am so convinced by the performance of a push pull tube amp (my speakers are 89 db at 4 Ohm) that I would like to build such an amp myself with KT88 instead of El34.

I have been looking around and found these two designs:

http://www.triodedick.com/monobill_deel_1.htm
scheme is here:
http://www.triodedick.com/monobill/m...versterker.GIF
Psu is here:
http://www.triodedick.com/monobill/m...%20voeding.GIF
(This design by Triodedick has got much laud by dutch diy folks).

and another design for 2 or 4 KT88:
http://jastrid.xs4all.nl/Dalojan/KT88_PP.html
scheme: http://jastrid.xs4all.nl/Dalojan/Schema_KT88PP.html
psu: http://jastrid.xs4all.nl/Dalojan/Sch...ng_KT88PP.html
scheme 4 KT88: http://jastrid.xs4all.nl/Dalojan/Schema_4_KT88PP.html
psu 4 KT88: http://jastrid.xs4all.nl/Dalojan/Sch..._4_KT88PP.html

The latter provides a balanced entry. Could one also modify the other amps with 2 KT88s for balanced operation?

Which one seems better on paper?

I am a newbie with regards to tubeamps.
To me, a good reproduction of space/reverb in a recording is paramount. And of course the ability to drive my speakers. Others have warned me that a SET would have difficulty here.

Any suggestion or hint is most welcome!

Lucas

In my experience SET KT88 should still provide plenty of power to drive a 89db speaker (my speaker is only 87db still run alright). it also depends on how big is your listening room bigger room less bass
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