The reverb recovery circuit is fairly straightforward.

Figure 1: The Accutronics Type 4 reverb pan The driver circuit takes the signal from the guitar amplifier's preamplifier and sends it to the reverb tank.Tube amps can hold and store potentially LETHAL voltages for some time after being unplugged, and they should never be opened up unless you know what you're doing in there.While other companies also manufacture tanks, the spring reverb "pan" or "tank" you'll find in more amps than any other is made by Accutronics.The driver and recovery circuits can be either tube or transistor based, but in many tube amps, tubes are also used for the reverb.We're going to keep things simple this time and stick to only things that can be done without opening up the amplifier.Fender used long decay time tanks in the vast majority of their amps, but other decay times are also available.If you want to shorten the decay time, use either a 4AB2C1B (1.75 - 3 seconds) or a 4AB1C1B (1.2 - 2.0 second decay time) tank in your Twin.