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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:  cnpope [ 14 Feb 2010, 01:18 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hmmmm... Maybe the CCS is operating outside its constant current range? A measurement of the cathode current (for example, by adding in a 1 ohm resistor between the CCS and the cathode, and measuring the voltage across it) would be interesting. Also, what is the cathode to ground voltage?

Didn't you say a while back that the CCS was passing 200mA, which was dragging the B+ way down? With 50 ohms in the
CCS circuit, it should only be about 1250/50 = 25 mA. And 200mA is much too high for that poor little 12B4A! Maybe the LM317 got fried, and now the "CCS" is just behaving like a resistor? Hard to say, without knowing the cathode current and voltage.

Anyway, whatever is happening, it seems it sounds good! That is what matters in the end!

Chris

Author:  Bennybuis [ 14 Feb 2010, 13:56 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hallo,

I believe the CSS is simply not working. I haven't had a chance this weekend to check on it, but I will. The first try with css was a failure anyway, bad LM317, which I reused in my kt88 amp which blew up a hundred € power transformer trying to save a little money. :blush:

Well, at the end it was a blessing in disguise, because out of desperation I used a power transformer which I thought would be not strong enough, but it is, so it is all good there now.

Back to my 12B4A amp. Gio let me have a link on how to figure out the primary impedance on opts, that I wanna try on the pseudo opts I am using for this amp. And I will demolish it and reuse the parts for my new pre amp headphone amp. I need a pre amp with phono in, on Thursday I will get a DUAL record player and I still got no RIAA pre amp, but that I will fix tomorrow. Still not sure if I want to use the 12B4A as the output stage for my pre amp (it is really primarily for headphone use) or use the ECL86b and trannies I got from a vintage DIY amp. Gotta sleep on that one one more night.

Author:  CrazzyAbtTubes [ 26 Apr 2010, 16:41 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

That amplifier looks great Ben, you try some better output transformers, it would really sing using Edcores. Maybe you should try a push pull amp when you get more 12B4's. ;)

Author:  Bennybuis [ 27 Apr 2010, 12:40 ]
Post subject:  Re: Small SE tube amplifier using 12B4A and ECC802S

Hi Allan,

well I am happy with those opts, they scope good enough, too. Till maybe 2 watts, they are HiFi quality even though, no air gap. More power and the little core will be saturated and it won't sound nice no more, but for the 12B4A it is a perfect match. That setup also gives a hell of an headphone amplifier, really. I am eager to build that again, using your 12B4A's.

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