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6B4G Push Pull Interstage Coupled Push Pull Stereo Amplifier

Built for Nikhil Suvarna of Redwood City, CA

Completed on 2/01/12

Those that follow my work would be familiar with my affinity towards buidling single ended amplifers, e.g. about 90% of my builds are single ended amplifiers. Having said, here is a build that might change that a little.

When Nikhil approached me to build this amp based on Ralph Powers schematic ( http://www.digitalakuten.com/circuits/ralph_amp/ralph-amp.htm), the first thing I did was to study the schematic. I have to admit, the circuit was by far the simplest PP circuit I have laid my eyes on. That was good. I like simple. I also read the following remarks by the designer, and I quote, "So you wind up with a sound that is not quite single ended and not quite push pull, but instead one that borrows the best from both worlds." I had to see for myself what that sounded like. See below for my comments:




Nikhil provided me with all the tubes and those beautiful Sansui 1000A output transformers. The Sansui tube amp legacy still lives on through Hashimoto products.



I replicated the circuit faithfully with an exception of the interstage transformers. The original circuit calls for the LL1635, but as per Kevin's (K & K Audio) recommendation I went with the LL1692A (25mA version) and it seemed work nicely.
My overall impression of the amp is very positive. I was trying to figure out what Ralph was saying about combining the best of both SE and PP and I seemed to have an idea what that might be. The amp has a plenty of the SE finese in the high to mid frequencies but with a lot more gusto at the lower frequency. The amp also sounds very balanced. It almost sounded like a very powerful 45 amp minus the speaker unfriendliness. I also love how simple the circuit is, e.g. no phase inverter tube to wire, no NFB, no bias circuit, etc. If you're looking for a relatively simple amp to build that will give you a hi fi performance, I would really give this amp a chance. Happy listening! Min

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