Simplified B-17B

The combined tube/solid state B-17 design is progressing and here is the schematic of the updated and much simplified version:

Note that the design no longer includes a complete solid state power amp, the voltage gain is handled by the 12AX7 tube and the solid state circuit is simply an emitter follower and a unity gain output stage. The tone controls have been moved between the two triodes and this means that only a single 12AX7 tube is required.  This is also the reason that no midrange control is added, to do this right would require another tube stage.

The solid-state portion has been modified for single-ended supply operation for simplicity.

This design does not currently have a provision for a global feedback loop so the distortion figures would be closer to a vintage amplifier than a modern solid state design.

This is still a very preliminary design but you can see how the concept is progressing.
More to come!

Back to the B-17

I’m back after a long hiatus for summer. For now I’ve set aside the tone control design and am working on combining the previous B-17 preamp with a solid state amplifier design. Here is the first cut – please don’t try to build this amp as the exact component values, etc. still need work.

The power amplifier is a standard 3-stage design with an old-school quasi-complementary output. I picked the venerable 2N3055 output transistors to start.

As I mentioned earlier, this circuit still needs a lot of analysis and design work before it is ready for building. For now it is useful for LTSpice analysis and trying out concepts.
Stay tuned!