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Oddwatt Push Pull Tube Amplifier Projects
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Author:  gofar99 [ 09 Sep 2008, 11:22 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi All, Project update. The replacement KT88 is functioning fine. I now have about 1-200 hours on the amps and all is well. I found another thread on the web about problems with JJ KT77 tubes. I have had no problems with them (I have 8) in either of the two amps that can use them. There was a good point in the tread. Make sure the grid resistor does not exceed 250K ( I use 220K). There is a problem then of drift. In all the Oddwatts this could be an issue as one grid is essentially on the ground with only 220 ohms in series and the other has 220K. This has not caused any problems I know of, but may explain why some tubes "like" to be in one or the other position. I have considered increasing the 220 ohm resistor in value to match the output impedance of the driver stage to see if it affects the symmetry of the output at high drive levels. BTW the symmetry is already quite excellent, I'm just a perfectionist at some things. If anyone has some thoughts on this, I would like to hear them either in the forum or PM to me. Full write up is close.

Good listening
Bruce

Author:  billp [ 09 Sep 2008, 20:46 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Bruce, I have enjoyed reading your tube amplifier projects and I am looking forward to reading about your KT88 version.

Author:  gofar99 [ 10 Sep 2008, 10:01 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Everyone, Another update. The first of the "Odd Mono-Blocks" is up and running. It will be in the project write up with the KT88 amps. It is quite similar in design. Lovely sound. I may need a bigger air conditioning unit with all these big tubes glowing in my listening room. There will ultimately be 8 KT88s or perhaps 4 KT88s and 4 KT77s. I haven't decided which sound better in the design. The 88s have more clout, the 77s seem a bit more refined. It could be the brands of tubes though.

Stay tuned for updates.

Good listening
Bruce

Author:  ejfud [ 10 Sep 2008, 12:53 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Any chance you're still thinking of offer kit versions of these?

Very cool amp!

Author:  gofar99 [ 10 Sep 2008, 14:26 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Ejfud, Yes a kit is still in the works. Now that the design is finalized the sourcing of parts and such are in progress. Originally there were plans to use a single main board for nearly all parts. The problem with this is that it severely restricted the actual case layout and types. A redesign is in progress to use three boards. One for each channel and one for the PS. The hope is to have some initial kits ready by Thanksgiving. At least that is the plan. I am also perfecting a "cheapskate diy" design that uses economy parts. It will not be as powerful nor as good sound wise in general, but has great potential for second systems in the house. Target is 8-10 watts/ch with under 1% distortion with a 30HZ to 20K response. It will be strictly point to point wiring and I want to source parts for diyers to build it at under $200 in parts. No kits are planned for that one at this time (perhaps later) and it could well be January before I get it sorted out.

Good listening
Bruce

Author:  ejfud [ 10 Sep 2008, 15:56 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Cool! Keep me posted.

Author:  Gio [ 10 Sep 2008, 17:25 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

gofar99 wrote:
I am also perfecting a "cheapskate diy" design that uses economy parts. It will not be as powerful nor as good sound wise in general, but has great potential for second systems in the house. Target is 8-10 watts/ch with under 1% distortion with a 30HZ to 20K response.

Second tube systems. Yes, we have problems! I hate to say it, but I am really looking forward to this! :up:

Author:  gofar99 [ 18 Sep 2008, 18:09 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Everyone, Second tube systems. I have 4 now. I'm going to have to invest in a bigger A/C unit if all are running at the same time. The Odd Block monos are complete. I have been running them for two days. Nice. They are presently using JJ KT77s and NOS RCA 12SL7s. IMHO a very good combo. Powerful and refined at the same time. A full write up is nearly done. I want to put a couple hours on the amps before full testing, but some causal inital results were quite similar to the OD225s. Much more to follow soon.

Good listening
Bruce

Author:  Endspec [ 18 Sep 2008, 22:03 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Bruce that is a nice looking unit. I am interested in a kit too, also might there be a kit for the EL 84 vertion of the odd watt line in the works?

Author:  gofar99 [ 22 Sep 2008, 18:08 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Everyone, I have the Odd Blocks up and running. A write up is nearly complete. They perform much like the OD225 (big surprise right). My initial listening is that they are better in some areas. Separation is better (mono-blocks will do that). It seems like detail is better as well and the bass is clearer. None of these things were bad before, just a little better now. Using JJ KT77s and RCA NOS 12SL7s I get up to 19 w/ch under .8% (went to 1.5% at 21 watts into 8 ohms) from 8HZ to past 19K. Down 1 db at 20K and 3db at 23K. That is intentional to prevent any chance of exciting the resonance of the transformers (at about 50-60KHZ). These are only rough first measurments. More to follow later.

Good listening
Bruce

On the possibility of an EL84 kit maybe, a 6V6GT is more likely though.

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