Amplifier 16: Triode push pull amplifier with cathode feedback

In amplifier 16 the screen grids are connected to their anodes. This means that half of the output power of the power tubes is available. The cathodes again are connected to the secondary winding of the OPT. This creates extra local feedback. Click here to download the measurement results.

The sound character of amplifier16 is very clear and detailed. Again this is a real high quality high end amplifier, but there is something wrong with this amp: he sounds boring. There is nothing to complain about, everything is extremely correct. In spite of all these goodies, the amp is not alive, he does not breath, he does not pull you into the music. It seems as if the extra local feedback has killed the lively character of the amplifier and has passed a certain frontier. By means of a story I can explain what happens in this amplifier.
Long time ago, in those days where even valve amplifiers did not exist, there was a tiny little man with a tiny little voice. His ideas were brilliant and he wished to tell the whole world about his gospel. To do so, he hired a tall heavy man, with mighty lungs and a huge mouth. His voice was so loud that he could make the walls of a town to collapse. There they went, the two of them, traveling all over the world to preach the gospel of the tiny man. While traveling from town to town, they discussed the gospel and after some time the huge man understood its content. When they arrived in a town, they immediately went to the marketplace. The huge man started to tell, while the tiny man stood besides him, very satisfied. Everyone clearly could hear the message and many disciples were the result. Years later, the tiny and tall men had traveled a lot, they started to irritate each other. The tiny man was not satisfied anymore about the wording of the gospel by the huge man. That really could be improved. He decided to control every muscle and even the lungs of the huge man. Now this big voice did exactly as he wished, without any mistake. The next day, they arrived at a town and the tiny man was very tensed about the results of his new approach of preaching the gospel. But the result was a disaster, nobody listened, people started to talk with each other and after a while they threw rotten eggs to the evangelists.
The moral of this story is that too much control kills the lively character of the amplification. Of course, this story is a very limited reproduction of what really happens, there are many more things to say about it. However, the essence is clear: too much control creates a boring amplifier. Somewhere a balance should be created between magnificent specifications and a pleasant musical reproduction. Going from amplifier 10 to amplifier 16, in my opinion, amplifier 15 has the right balance for true musical high end reproduction.

Next time: amplifier 17