I spent a good portion of yesterday doing the final assembly on the headphone amp. All I had left this morning was to wire up tube and pop the top on. I plugged in the power and…
In the words of Isiah Whitlock Jr.: Sheeeeit! The LED was flashing, it’s not supposed to flash.
After a bit of poking around with the meter, I found the problem: I wired the LM317 regulators improperly. The output was shorted to ground. I carefully disassembled enough to get to the bottom of the circuit board and rerouted a few things. Once the LM317 was wired up correctly, it worked fine. I’m a bit surprised that the components stood up to such abuse.
Here’s the final product playing some classic rock: