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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:  moonbird [ 11 Feb 2010, 02:40 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Bennybuis wrote:
... a little while ago I build a simple amp for my telly using those output transformers I got from Magnus and the 12B4A ...

Ben - Would u mind sharing the schematic for your 12BA4 guitar amp. I also play a tele guitar and might try to build it. Thank you.

Author:  Bennybuis [ 11 Feb 2010, 15:02 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi Jim,
sure. Here you go.
Attachment:
12B4A simple amplifier.jpg

That is the output stage, sounds very good, here comes the complete amp with css, the css resistor is wrong, should be 50 ohm or so.

This amplifier is worth building it, Jim, I will build it definitely again

Author:  moonbird [ 12 Feb 2010, 15:43 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Bennybuis wrote:
... here comes the complete amp with css, the css resistor is wrong, should be 50 ohm or so

Hi Ben -- thansk again for posting this? I am confused - is there a preamp???? Plus I don't see a css or at least what I think a css is. Looks like a common bypassed cathode bias setup to me -- am I missing something :confused:. Did you get a chance to post everything? Thanks again for your time Ben.

Author:  Bennybuis [ 12 Feb 2010, 16:22 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Sorry, wrong picture, here comes the complete schematic, just the css resistor should be 50 ohm at 275 volts B+
Attachment:
12B4A amp.jpg

Author:  moonbird [ 13 Feb 2010, 00:27 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Bennybuis wrote:
here comes the complete schematic ...

Thank you Ben for your continuing kindness. This looks like a fun amp to build - I will do this one first. Can yo tell me which leads you used on the 100V Output transformer? I think Magnus sent me a picture. Better yet could you measure the DC resistance between the two primary leads? Then I can try to reproduce that her. Thank you again Benny - you are nice to help me.

It is strange I still have not received the sub-minis. I am not mad at you or anything. It is just strange huh?

Author:  Bennybuis [ 13 Feb 2010, 00:44 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi Jim,
I used the Yellow and black leads for the primary, yellow going to the plate of the 12B4A and black being B+. Wait if I can dig up a picture.
Attachment:
output transformers.jpg

And the two leads on the other side, I think its red and black, black is ground and red is output. To the primary leads, yellow and black works real good with 12B4a, so good, that i didn't try the other leads, to my shame. Maybe another one will work even better, you are welcome to experiment. Please share any improvement you may find. I am using this amplifier every day for as long as my telly is running, and my lay is watching a lot.

Author:  azazello [ 13 Feb 2010, 03:58 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi, Ben!
How is the resistance between yellow an black primary, compared to another prim. wires?

Author:  Bennybuis [ 13 Feb 2010, 07:54 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi Nikola,

measured with a cheap multimeter it is about 400 ohm, all the others are less impedance.

Author:  cnpope [ 13 Feb 2010, 11:14 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Ben, I am puzzled by the role of your CCS in this schematic. If the cathode current is constant, then so is the anode current, and hence no audio output at all. (Quite a different story from a PP design like the Oddwatt, where the *total* current through the two output tubes is constant, but the relative proportion through each is varying with the signal.) But for SE amps, surely a constant current through the output tube is not what is wanted?

Chris

Author:  Bennybuis [ 13 Feb 2010, 14:11 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Well, I get your point, you are right! But why is my amp then working, and good, too? I am listening to it right now, it is connected to my main television and running all day long (My wife is a real TV baby),


Cheers

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