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Small SE tube amplifier using 12B4A and ECC802S
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Author:  Bennybuis [ 09 Jan 2010, 04:14 ]
Post subject:  Small SE tube amplifier using 12B4A and ECC802S

Hallo everybody,

a little while ago I build a simple amp for my telly using those output transformers I got from Magnus and the 12B4A, also from Magnus. I did like the sound of the 12B4A's a lot. The amp I had to take apart for the tube sockets, they are now in my new amp with the 4 GU32, but I got more sockets yesterday :) so I can build another one of those little amps, this time I want to build a bit a better amplifier, using a better filtered power supply, DC heating and a real pre stage. And I am gonna paint the output transformers nicely black :) My aim is 1 to 1,5 watts pure triode power, that must be to archive with this setup. Anybody got any suggestions, feel free. One of the cigar boxes, I already prepared for tube amplification, sanded the prints away (took a long time of sanding) and painted it with clear coat many times, it has now a nice closed surface.
Attachment:
12B4A amp.jpg
Attachment:
Cigar boxes.jpg

Author:  azazello [ 09 Jan 2010, 10:51 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi, Benny!
How many volts on B+ ?
Can you try to disconnect FB 3,3 kohm & 470pf and compare both variants.
I lake Your cigar box /please, keep 1 for me !/.

Author:  Bennybuis [ 09 Jan 2010, 14:39 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hallo everybody,

well I am still preparing parts, painting and waiting, tomorrow, I will start putting things together. Here are some pics of the status quo.
I will have about 275 volts of B+ with those transformers.

Author:  Bennybuis [ 09 Jan 2010, 15:05 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi guys, so now everything is painted, cool. I will wait over night to have everything dry enough to handle. Not having cut any holes into the case for the tubes, I get second thoughts, maybe I use different tubes, instead of 12B4A I could use a GU50 in triode mode and just choose a tap on my output transformers, that has the least distortion. That would give me like 5 watts or so. Could that work? Any suggestions are welcome.

Author:  Bennybuis [ 09 Jan 2010, 16:33 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Well, here is the beginning with the high voltage transformer in place. Now I gotta let everything dry overnight and tomorrow I will put that thing together, I got most of the parts in house, missing a couple of caps and resistors, as usually.

Author:  Bennybuis [ 09 Jan 2010, 21:47 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi guys,

my cigar box starts looking like a tube amp!

In the morning I will cut the holes for the tubes. But what tubes to use? I think I will just stick to schematic and use up my 12B4A.

Author:  azazello [ 10 Jan 2010, 03:44 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi, Ben!
Of course, 12B4A,.... Output and main transf. on Your box are very small for GU50.
/GU50 needs for SE 400v, 100 ma, fixed-Ubias 30-35v, or very power Rk , 12,6 v and output transf. 10-12 sq.sm/.

Author:  Bennybuis [ 10 Jan 2010, 05:45 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hallo everybody, here are the pictures of the latest development. Much more I cannot do today, I am missing parts, as usually, not many, just a couple of resistors and caps. But here is how it's gonna look like, not bad for a days worth of work, I suppose, 24 hours ago that was just an empty cigar box with company name burned into the wood all around.

Author:  Bennybuis [ 10 Jan 2010, 13:01 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Well, I started to wire that thing: here is how it looks so far.

Author:  Soundbrigade [ 10 Jan 2010, 13:28 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

You should stop there and not mess things upp with loads of components and wires .... :smoking:

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