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The "Unnecessarily Complex 300B Amp"

Having never built a single-ended 300B amp, I figured the right thing to do would be to go overboard.  So I designed and built this:

There is an article in audioXpress magazine (May, 2009) I put together on this, so I won't post all the details about the design and construction - please buy the magazine!  But I will post detailed photos and schematic here that are more readable than those in the magazine.

Here is the schematic (39kB PDF file)

I started with a single-stage driver using a triode-connected EL802 (you could also use the plentiful PL802 but would need a separate filament transformer).  The EL802 design performs a little better than the one above (a 2-stage driver using 7044/7119/5687), but suffers from lower gain and high input (miller) capacitance, so it is problematic to use with a passive volume control.  But if you intend to drive this with a preamp that has an output impedance of less than about 10kohms, and some gain, this might be a better choice.  Here is the schematic (17kB PDF file).

Also, a schematic of a more conventional power supply (19kB PDF file).  Note I have not built or tested this!

Mechanics: I'll post source CAD files as well as some PDF files for this as I built it.  If you have access to CAD tools or want to use Front Panel Express to make the top plate, even if you plan on using some different parts (like transformers), this will give you a big head start.

Here's a PDF plot of the AutoCAD layout, viewed from the top (154kB PDF file) or viewed from the bottom (144kB PDF file).

If you have AutoCAD or a compatible CAD program, you can download my mechanical drawing in .DXF and .DWG format (406kB ZIP file)

If you want to use Front Panel Express, here is a ZIP archive with my FPE files (2kB ZIP file)

Pictures:  Below are photos of the amp as built.  The 640x480 thumbnails are linked to full-size images that you can zoom into for better detail...

And just because it looks cool...