Thorsten wrote:

Not quite. What is wrong is not the Amplifier, but ....

Interesting, I was searching the reasons of the headphone’s headache (read above) and I it looks like there was no oscillations (they should be seen on the 100MHz scope). However, while I was “there” I decided to look at the frequency response of the Little Amp. It looks very nice (the possitive feedback was disconnected for now):

Each square is .45V. I was not able to drive the Little Amp into the clipping. I drove it with 10.5V input as my generator does not output more. The above is 1000Hz

Above is 100.000Hz

Above is 20Hz. Longer exposure to get the entire wave.

Above is 5Hz. Longer exposure to get the entire wave.

Over the course of the past year I was very slowly experimenting to the sound of my headphone amp. I know much more about it sound then I knew last year and I learned a lot more how to get “different” sound from it. The more amps ages and the more I am familiarizing myself with its sound the more I hate this damn thing. I usually take a headphone amp at my work and listen though it during operation time but over the last year I find all imaginable justification not to do it. I made a number of changes with the amplifier trying to get out of it any more or less civilized sound but whatever I did made me more and more to hate this amp. Well, the smartest thing is to declare the entire project as a complete fiasco and to forget about it. So, I do…

Still, there are some afterthoughts that I feel are worth to share…

Now I know defiantly that the problem of this headphone amp was my selection of the 6C19P tube. The 6C19P is hell of a tube and it has a very good reputation in Russia. It is very linear, it has very low plate resistance and many Russians call it “baby 6C33C”, some even claim that 3 parallel 6C19P outperform one 6C33C. The Japanese love to use 6C19P for OTL,  of course it a very good regulator and have seen in US people use it in preamps… Wonderful tube, isn’t it?

http://www.tubes.ru/techinfo/GlassTubes/6c19pv.html

Well, the data looks very good, the audio on 6C19P measures OK but the reality of sound with this tube is a cleats and undeniable evidence that this tube should not be used for Sound under any circumstances. Probably in regulators it would be OK, I built a few regulators on it – was not impressed with their pound – but it was not the end d of the world. However, when you begin to drive actual sound via the tube then it acts as a nightmare. I never have head so harmonically stupid tube that juts push out a very high quality independent frequency without any understanding that those frequencies are part of Sound - no wonder that Russians love it. In other worlds the tube is sonic deserter and form what I have learned it should be avoided at all cost.