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Small SE tube amplifier using 12B4A and ECC802S
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=1358
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Author:  Beftus [ 13 Jan 2010, 17:24 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Bennybuis wrote:
That is also a killer headphone amp, really. That little thing really rocks. Idid all the little improvements, like grounding the filament circuitry with 0,01 uF respectively to ground, that made it even more quiet.

Could you show and tell what exactly you modified in the JAN6418 thread? Thanks.

Author:  azazello [ 13 Jan 2010, 17:28 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

HI!
Where I can buy 12B4A? I lake it's Ri - 1 kohm!

Author:  Soundbrigade [ 14 Jan 2010, 03:12 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

azazello wrote:
Where I can buy 12B4A? I lake it's Ri - 1 kohm!

I can send you a pair. Guess I still have some left. I also have some CDs for you but I have mislaid them ... :confused:

Author:  Bennybuis [ 14 Jan 2010, 03:51 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hallo everybody,

well here is the final schematic, just like I build my amp. Any suggestions are as usually more than welcome, since I don't really know what I am doing, I kind of get liucky :smoking:

Author:  Bennybuis [ 14 Jan 2010, 04:08 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Note, tat the 8,2 uF poly cap located on the amp schematic is located right where the two output transformers are connected together for B+ and this cap is common for both channels. Should be really 10 uF, if you can get them, I can not, or almost not, got only one and wanna keep it for a "serious amp".]
Anyway, I closed the lid on that little amplifier and I am so ready to start something mew, I am already sanding the bigger cigar box.......

Author:  azazello [ 14 Jan 2010, 07:10 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

BEN!
Connect el. cap 100 uf from cathode preampl. direct to ground, not between meddle point of resistors!
It will be better to sounding!

Magnus!
Thanks!

Author:  Bennybuis [ 14 Jan 2010, 12:02 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hallo everybody,

Nikola, you are right about the 150 ohm resistor, it is only there, because I wanted to feed it NFB to this point, but since there is no feedback, I can take the resistor out and replace the 330 ohm with 470 ohm, it will sound even a bit better. But I am not sure yet, if the amplifier really doesn't need any feedback, with my ears I cannot determine that, I tried, the differences to hear are to small to adjust the feedback loop by ear, you can surely do that with the proper amount of experience, but this I lack as well.

Author:  azazello [ 14 Jan 2010, 13:18 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

BEN!
How is anode current of output tube and pre tube? You can measure U every cathode ...I=U/R.

Author:  Bennybuis [ 16 Jan 2010, 00:09 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hallo Azazello,

I have across the cathode resistor 21 volt, does that help? Otherwise I have to unsolder and measure with the multimeter.

Author:  azazello [ 16 Jan 2010, 03:48 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Ben!
You have 26 ma for output tube. It's small for good sound. Put in cathode 620 ohm/3-5 watts
to increase current to 35 ma.Try to change ECC83 to 12AT7 and resistors 470 ohm to 220
and compare the sounds....

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