Fender Twin Reverb — No Reverb (Dead Recovery Tube)

Symptom

Reverb completely absent. Not weak — fully gone. Reverb knob from 1 to 10 produced no change in the dry signal whatsoever. Amplifier otherwise sounded normal: loud, clean, full output.

Diagnosis

First suspect was the reverb tank — easiest and most common failure point. Opened the tank and found a broken wire on the transducer inside. Resoldered the wire carefully. Reinstalled tank, reconnected RCA cables. No change — reverb still absent.
Swapped the RCA cables and cleaned the jacks. No change.
With the tank and cables ruled out, fault moved inside the amp. The Twin Reverb reverb circuit uses two 12AX7 tubes — one to drive signal into the tank, one to recover the signal returning from the tank. If the recovery tube fails, the tank can be working perfectly and nothing comes back. Swapped the reverb recovery 12AX7 with a known good tube.

Fix

Replaced the reverb recovery 12AX7 tube. Reverb restored immediately — full splash and decay returned on power-up. Amp verified at multiple reverb settings. Original broken wire inside the tank was left resoldered as found; the tank itself was not the cause of the fault.

What I Took Away

Classic example of a repair that took an extra step. The broken wire in the tank was a real find and looked convincing as a root cause — but the actual fault was the recovery tube downstream. The tank fix was real work that needed doing anyway, but the tube was the reason there was no reverb. Follow the signal path all the way through before closing a fault.