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Oddwatt Push Pull Tube Amplifier Projects
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Author:  gofar99 [ 24 Sep 2018, 16:23 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, There are two of us amazed on the anodizing on the heat sinks. Yes the LM317s should be fine.

Good listening
Bruce

Author:  JoshP [ 25 Sep 2018, 09:38 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hey Bruce, I've just replaced the LM317's and used the insulators, all back to normal now, although sadly one of my tubes didn't withstand the punishment, but I've got some old spares to keep me going for now.

thanks very much for all the help, massively appreciated as always.
cheers
Josh

Author:  gofar99 [ 25 Sep 2018, 14:31 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, It still boggles my mind that they worked at all.

Good listening
Bruce

Author:  Trackhappy [ 01 Oct 2018, 03:33 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Just an update on my recalcitrant amp... As per Bruce's recommendation I put a 270 ohm (closest to 250) in place of the 317 and powered up. As soon as the B+ came on, it briefly glowed red and destroyed itself. I checked resistances on each pin to ground and across the transformer, and found no anomalies. So I plucked up the courage, replaced the 317 and swapped the tubes from the good channel (disconnected the B+ from that side temporarily). Powered up and nice clean sound from that side. So issue is definitely the tubes. I am hoping the supplier will replace them.
I also did cold checks from pin to every other pin but no issue. Powered the heaters, and got down to about 2 Megohms from cathode to the grid on one tube, and 4 Megohms on the other. I don't know whether that is bad or not.
Cheers,
Glenn.

Author:  Emsworth [ 16 Oct 2018, 07:54 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hello to all.
My Oddwatt stereo was built to replace a defunct Akai 1175 receiver (75 wpc and lots of bass).
I expected the Oddwatt bass to be less pronounced ( i.e. more realistic!) than the previous amp and have given it several months of listening to let my hearing adapt.
The net result is that whilst I love the overall sound of the Oddwatt (I listen to a lot of jazz) I would still like more bass punch in orchestral and rock music.
My Oddwatt spec. is currently 6n1p / el34, with .33uF PIO caps.

I'd welcome suggestions as to where to start and what I can realistically expect to achieve. Any ideas?
Many thanks,
Denis

Author:  gofar99 [ 16 Oct 2018, 15:41 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, I suggest you try JJ KT88 tubes. Other brands will work, but I have been notified of problems with EH and Psavne branded ones. IMO EL34s have a nice sound, but as you noticed lack in bass. Set the idle current to each tube at about 90ma. If you are already using a 10 ohm resistor to program the LM317s just parallel it with a 22 ohm one to get the right current. Be sure that there is always a resistor in place when the power is on. If even for a really brief time there is none the LM317 will fail because of over voltage.

Good listening
Bruce

Author:  Emsworth [ 17 Oct 2018, 02:23 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Bruce,
OK, thanks for the suggestion. Currently I use a seperate switch for the HT supply and want to add a timer delay as a little project over the next month - I'll try this change at the same time and we'll see how it goes.
BTW, the amp is very stable and completely trouble free. I would recommend it to anyone.
Denis

Author:  Danny [ 25 Oct 2018, 11:16 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Team,
I wonder if you can give me some suggestions on how to try to fix this.
Few months ago I built 2 OddBlocks (using KT88s & 5751s) with subwoofer outputs. They sound great with lots of power. Good bass & clarity, except for some background/white noise which you do not hear when playing music but you hear it even at a 8 feet distance from the speaker. Again, maybe it’s just me. But, it is starting to annoy me. The noise is the same regardless of the volume level.
Any suggestions on what can be causing this?
Any help/suggestion is appreciated. Thanks,
Danny

Author:  gofar99 [ 25 Oct 2018, 21:44 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, Something is very wrong. There should be virtually no noise. My speakers are 92 and 96 db/w so slightly more efficient that most. There is nothing audible beyond about 2 inches. That is the way they are supposed to be. First, is the negative feedback setting correct? If it is backwards this can cause oscillation and may sound like noise. Second, what is hooked up to them? Try shorting the inputs and see if the noise goes away. If it does then the problem is in the equipment feeding them. Let us know what you discover.

Good listening
Bruce

Author:  Danny [ 26 Oct 2018, 08:58 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Bruce,

Thanks for the reply. My speakers are also 96 db/w. FYI - The noise is not hum or buzz. It is background/white noise as the sound of rushing water in the far distance.
Questions:
1) Not clear what you mean by the negative feedback setting being correct and not backwards. The 8 ohm speaker output of the transformer is currently connected to the negative feedback SPST switch. Which is normally in the open position (negative feedback off). What do you mean by backwards?
2) By shorting the inputs you mean just connect a cable having RCA connectors between the two inputs, correct?

Please, let me know. Thanks,

Danny

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