Fender Vibrochamp Repair

Specifications

• Serial number: A609298
• Circuit: Fender AA764, all-tube combo amplifier
• Output: Approximately 5 watts from a single-ended, Class A 6V6 power stage
• Tubes: Two 12AX7 preamp/tremolo tubes, one 6V6GT power tube, and one 5Y3GT rectifier
• Speaker: One 8-inch speaker with a nominal 4-ohm load
• Controls: Volume, Treble, Bass, Speed, and Intensity; two instrument inputs
• Effect: Tube-driven tremolo

Download the Vibrochamp Repair schematic (AA764 PDF)

4/17/2024

Andrew and i fixed the vibrochamp

We re-soldered the filter-capacitor connection. Vibration from the internal speaker was opening the intermittent ground connection and disrupting the power-supply filtering.

With an external cabinet connected, the chassis did not vibrate as much and the fault did not reproduce.

The single-ended 6V6 power stage conducts through the full 360-degree signal cycle. The tubes tested okay.

3/22/2024

Took it to andrew R. to test

Worked normally with an external cabinet and produced no unusual sound.

The fault returned with the resident speaker, pointing to either the speaker or a vibration-sensitive connection inside the amplifier.

3/12/2024

Swapped the 6V6GTA—the amplifier's single power-output tube—because the amp was not producing sound.

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