Single-Ended 807 Amplifier
This amplifier was built on-the-cheap. I used salvaged transformers purchased well below online prices and 807 tubes which are still reasonably priced. 7 watts per channel. I won an impromptu local “shootout” with this. Recently added speaker/headphone switch and headphone jack. Now it’s personal!
How it was done: Single-ended pentode mode, with primary-side feedback, and fixed bias operation.
A look at the construction:
Just wondering why you didn’t use a bypass capacitor on the cathode of the 807.
Ah, look again! It’s a fixed bias circuit, not cathode bias. The 10 Ohms are present for allowing the current level to be measured (50ma = .5V). Very little degeneration at 10 ohms, bypass isn’t needed. Ignore the schematic comment, it’s .5V not .05V.
Wondering what the FWB is? Also, can the feedback be eliminated with minimal affect? Russie
Full Wave Bridge. That power transformer had a bias winding. If you use one with only a bias tap, adjust accordingly. Feedback is really necessary for this, or it will sound BAD. If I were ambitious, I might change the output to triode-connected 6DQ6 and redesign the driver. That could work without feedback, kind of a poor man’s 300b amp.