The wiring on the top plate for the 6EM7 “Bloodwood” Amplifier is essentially complete.
But as I was just looking at the picture I realized that I had not included the ground tie between signal ground and chassis ground. So one wire short. Here’s what it looks like.
The layout is actually pretty clean. Individual stage power filters are at the top underneath the output transformers. The signal sections are below, wired directly to the octal sockets.
There are a few minor changes to some circuit values. I will post both an “as built” schematic as well as an “as designed” schematic including acceptable substitutions when I post the final project page. The next step is to install the top plate on the chassis and wire in the mains, panel indicator, primary filter choke, volume control, and speaker terminals. Then it will be time for some testing.
As always, questions and comments are welcome.
Is there a concern of hum with the chokes mounted underneath the output transformers? What speakers do you use? What is the sensitivity?
There is no concern with choke placement. Buy the time the B+ gets to these the ripple level is very small. Any radiated external magnetic field is far too low to cause any problems. I use a variety of speakers. I generally like higher sensitivity 2-way cabinets in the 90dB/W @1M sensitivity range. I haven’t measured the amplifier sensitivity yet but the calculated is around 300mV rms/W. I’ll have better numbers once the detailed measurements are complete.
Thank you