Single-Ended 807 Amplifier

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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!

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How it was done: Single-ended pentode mode, with primary-side feedback, and fixed bias operation.

A look at the construction:

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4 thoughts on “Single-Ended 807 Amplifier

  1. 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.

  2. 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.

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