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Oddwatt Push Pull Tube Amplifier Projects
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Author:  knightsofni [ 29 Apr 2020, 10:33 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Awesome thanks guys!
My only experience is with guitar amps so there is a bit of a learning curve.
And thank you Bruce for sharing your designs and knowledge.

Author:  metaldog99 [ 12 May 2020, 11:26 ]
Post subject:  Latest schematic

Hello, all -

I finally finished my Groovewatt build, and I now plan to build the Oddwatts. The Groovewatt sound is phenomenal. It surprised me.

I have found several schematics for the power supply dated from 2012 and 2013, with different titles:

  • May 19, 2013: "Power Supply for Oddwatt Audio KT120 Power Amplifier"
  • March 13, 2012: "Unified Schematic for Oddblock Amplifier Power Supplies"
  • February 22, 2012: "Oddblock Octal Power Supply"]

Are any of these the most current version to use? I plan on using KT88 or KT120, as my current speakers are power hungry and inefficient. I will consider biamping and building 4 mono blocks, but that's further down the line, of course.

Thanks in advance,


Author:  HT Performance [ 12 May 2020, 12:20 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

If your speaker are inefficient and you donĀ“t pretend to upgrade, then my advice is to go with KT150...



Author:  gofar99 [ 12 May 2020, 13:57 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, What are your speakers? The actual difference in the power available (remember this is class A operation not AB) between KT120s and KT150s is unlikely to matter. The change in loudness is a logarithmic function. 10-20% more power is not going to give you 10-20% more sound. More likely about 5%. IMO not worth the extra cost for KT150s and the transformers needed to handle the DC current. The KT120 Oddwatt outputs consume close to 300ma all the time. This is pretty substantial and I had to go to 70 watt transformers to keep them from saturating. With KT150s I suspect that 100 watt ones would be needed as well as a larger power supply. Think....costly. BTW I use a quad of KT88 amps on my system. It is however about 92 db/w for sensitivity. The unified PS is the one to use although any PS that can deliver the voltages and currents is fine.

Good listening

Author:  metaldog99 [ 12 May 2020, 14:19 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

My speakers are sealed Ellis 1801b's that I built many years ago. They work nicely in my listening area They are about 85dB sensitivity. I would assume 40 watts or so output is plenty? They are currently being driven from a ca. 1980's Adcom rated at 100 watts per channel 8ohms, 150 into 4ohms, 2.8dB headroom.

What is the approximate voltage output of KT88 vs KT120 build?

Author:  gofar99 [ 12 May 2020, 21:37 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, The power output for the KT88 amps is between 25 and 33 watts RMS and 40-45 watts RMS for the KT120 version. There are several variables on the exact levels such as brand of output transformer, actual B+ voltage and so on. I am not familiar with your present amp, but if it is solid state they do need to be be larger than a tube one for similar levels of loudness. Contrary to often mentioned watts are not bigger than SS ones. Watts are watts. The reason is that most SS amps when pushed hard clip horribly and sound really bad. You need extra headroom to stay away from that. Tube amps (these included) overdrive much more benignly and don't need the extra head room. They usually compress the signal on over driven peaks. I can use a 5 watt rms per channel Poddwatt on my ESLs and listen at a pretty loud level and not get any distortion from running out of head room. I normally use the KT88 size amps on them with KT120s running at the KT77 (lower) power level. The sound is really nice. It has something to do with the physical construction of the tubes. Power output then is right at 19 watts RMS. It can get much louder than I can stand . I have a pair of the KT120 amps but prefer the mid size amps. The KT120 amps are quite nice and the differences between them and the smaller ones are sonically minimal, but the heat generated is hugely bigger. You certainly would find the big ones adequate, perhaps overkill depending on your room size and music tastes.

Good listening

Author:  dimitris1811 [ 15 May 2020, 13:23 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi to everyone. I have built Kt88 and Kt120 PP monoblocks, following Bruce drawings with excellent results. Now I tried another one but tried to have pre amp and two KT88 PP monoblocks in a tower arrangement as an experiment. First operation attempt was ok but some humming observed. I did some rectification work and tried again but sound now is too low. I checked preamp stage with another amp and is ok. Then checked both channels power supply and is fine. Also, changed all tubes ... but same. Too low sound although seems clear
Any ideas? Filaments ok

Author:  dimitris1811 [ 15 May 2020, 13:41 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Is it possible to be the LM 317?

Author:  gofar99 [ 16 May 2020, 16:09 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, If the values when you balance the tubes are normal then the LM317s are fine. The values will be way off if the LM317 has failed. I would suspect a wiring error or a serious mismatch of the components. (preamp to amps). If you indicate exactly what you are using and how it is connected we can probably assist.

Good listening

Author:  dimitris1811 [ 17 May 2020, 09:06 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Thank you Bruce. I attach the schematics that have not been changed comparing to the attachment. Same was built as monoblocks with separate pre-amp, but now I try to do it as a tower with monoblocks and 4S-CF pre-amp all in one place.
Today I managed to bring back in operation one channel with a small hum.... it was a cable only well hidden!!!
Then I tried to fix second channel and found again something out of place (it is too heavy and difficult to access). When tried it I heard a hisssss and no voice. I changed tube and problem solved. But that was temporary testing. I re-assembled all tower and when tried it hisssss came again. I changed again 3 valves, all new but nothing happened so far. I suspec something with tube socket (audio note new) or attached wiring. But it is strange to me how i listen this hisssss like empty radio signal, and no sound at all. Any ideas on this?
The small humming remained in one channel is affected by the volume so I suspect something from input jack to pre-amp input

Note : I used 6SL7 tubes

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