Uploaded August 2026 | Updated September 2026, 2 weeks ago
Welcome to the beginning of a new Blueglow Electronics series focused on one of Fisher's classic little tube amplifiers, the Fisher 30-A.
In this first video, we'll introduce the amplifier, take a look at its overall design and schematic, and lay the groundwork for a much deeper circuit analysis in the videos that follow.
Rather than simply discussing how to restore a Fisher 30-A, this series will focus on understanding how and why the amplifier works. We'll work our way through the circuit section by section, examining the engineering decisions Fisher made and using real-world measurements and calculations to see how closely theory matches what we find on the bench.
Throughout the series, we'll dig into the power supply, ECC83/12AX7 voltage amplifier and phase inverter, push-pull EL84 output stage, output transformer, biasing, gain, negative feedback, frequency response, stability, and other aspects of the design.
We'll also work through many of the calculations ourselves, including operating currents, tube gain, open-loop and closed-loop gain, feedback, RC filtering, power-supply ripple, load lines, and output power.
The Fisher 30-A may look like a relatively simple amplifier, but there's a surprising amount of interesting engineering packed into this little chassis.
If you enjoy vintage tube audio, circuit analysis, amplifier restoration, and learning not just what a circuit does but why it does it, I think you'll enjoy this series.
Thanks for watching, and welcome to the Fisher 30-A deep dive.
===
Video Breakdown:
0:00:00 - Introduction
0:02:42 – The Fisher 30A
0:03:05 – The Schematic
0:06:38 – MATH!
0:09:23 – Component Can Play Multiple Roles
Welcome to the beginning of a new Blueglow Electronics series focused on one of Fisher's classic little tube amplifiers, the Fisher 30-A.
In this first video, we'll introduce the amplifier, take a look at its overall design and schematic, and lay the groundwork for a much deeper circuit analysis in the videos that follow.
Rather than simply discussing how to restore a Fisher 30-A, this series will focus on understanding how and why the amplifier works. We'll work our way through the circuit section by section, examining the engineering decisions Fisher made and using real-world measurements and calculations to see how closely theory matches what we find on the bench.
Throughout the series, we'll dig into the power supply, ECC83/12AX7 voltage amplifier and phase inverter, push-pull EL84 output stage, output transformer, biasing, gain, negative feedback, frequency response, stability, and other aspects of the design.
We'll also work through many of the calculations ourselves, including operating currents, tube gain, open-loop and closed-loop gain, feedback, RC filtering, power-supply ripple, load lines, and output power.
The Fisher 30-A may look like a relatively simple amplifier, but there's a surprising amount of interesting engineering packed into this little chassis.
If you enjoy vintage tube audio, circuit analysis, amplifier restoration, and learning not just what a circuit does but why it does it, I think you'll enjoy this series.
Thanks for watching, and welcome to the Fisher 30-A deep dive.
===
Video Breakdown:
0:00:00 - Introduction
0:02:42 – The Fisher 30A
0:03:05 – The Schematic
0:06:38 – MATH!
0:09:23 – Component Can Play Multiple Roles
