This guitar amplifier has been equipped with four 6L6 tubes.
Fender Twin Reverb amplifier, front view
At this moment, the amplifier has three anomalies and is being repaired now : One 6L6 has turned white, most likely due to the loss of vacuum, one magnetotransformer of the reverb unit has a broken wire and a 10k potentiometer has a damaged shaft.
Chassis after some thorough cleaning
I saw this collection of LP's in Utrecht recently...vinyl ("LP's") is back. A perfect combination with tube amplifiers!