amp repair, amp tech,Guitar,Effects,valve amplfier,Vintage Amplifier,Amplifier Mods,Amplifier Service,Amp Service, Devon, Cornwall, Lewdown, Okehampton, Launceston, Plymouth, Bude, Exeter, Teignmouth, Torquay, Tavistock

How a Reverb Tank Works

When an electrical signal is applied to the input coil a magnetic field is generated which acts upon a tiny magnet on each of the springs. This field causes the magnet to twist. This movement then propogates up the helical spring until it reaches the output coil. So, at the output coil, the twisting motion of the magnet produces an electrical signal that is a delayed version of the original. In addition, the twist is reflected back up the spring to the input and then again back to the output coil. The process continues with sound bouncing up and down the springs, getting quieter each time so giving a seres of reflections just as though you were between two walls.

These movements are very small, therefore it is important to prevent any external vibrations from getting into the mechanism. This is done in two ways. First the springs are mounted on a metal tray which is then suspended into the larger outer housing. Second, the outer housing has four rubber mounting feet with brass inserts to damp vibrations transmitted via the mountings.

What's Your Orientation?

Reverb tanks are pre-adjusted to be mounted in certain orientations. On the short 9.25in long tanks the inner tray mounting springs are strong compared to the weight of the tray and so can usually be mounted in any orientation as gravity has little effect. For the longer 4 and 9 series ones the tray is much heavier and so the tray mounting springs are located in different holes on the outer chassis to prevent the inner tray from touching the chassis. So, if you were to take a tank specified for open side down mounting and turn it upside down you will see that the inner tray is touching the chassis. Similarly for input connector up and down mounting. It's just a matter of moving the mounting springs to keep the inner tray away from the chassis. It's quite easy using a pair of needle nosed pliers to move these springs if you can't get the style you want off the shelf. The last letter of the part number specifies the pre-adjusted orientation.

  • A - Open side up
  • B - Open side down
  • C - Connectors Up
  • D - Connectors Down
  • E - Input Connector Up
  • F - Input Connector Down


There is an old Accutronics tank application note in which they state that the magents are set differently between orientations. Since the mangnets are rotated by the applied signal and the displacement due to gravity is negligiable, this does not seem to apply to the modern tanks that we supply. This has been confirmed by the tests we have done. Therefore, by simply adjusting the suspension springs you can use them in any orientation.

Styles of Reverb Tank

The sonic differences between the reverb tank styles are a consequence of the different mechanical components. The 8 series of tanks, i.e. the first character in the part number is "8", are a short 235mm tank with three springs, the 4 series are longer at 430mm with two springs and the 9 series are 430mm with three springs.

To give you some idea of the difference between these types here are some soundbytes comparing four types that you can download and listen to.

8 series medium decay.mp3
4 series medium decay.mp3
9 series medium decay.mp3
4 series long decay.mp3

Connector Grounding

The input and output connectors can be connected to the chassis. The specific arrangement required depends on the associated electronics and is beyond the scope of this article. The good news is that all the reverb tanks we supply can easily be re-configured to any of the four possible arrangements. The pre-configured grounding scheme is denoted by the 5th character of the part number.

  • A - Both Grounded
  • B - Input Grounded
  • C - Output Grounded
  • D - Neither Grounded

If you need to change the grounding scheme of a reverb tank, here is how to do it.

Replacing a Reverb Tank


Reverb tanks usually fail for one of a couple of reasons. They contain two coils with very fine wire and this can break over time. The springs can slowly stretch under their own weight and foul the chassis. In either case the best option is to replace.

The reverb is secured to the frame with four screws, sometimes it it also enclosed in a bag and you just have to figure out how to get that off. Most importantly, don't disconnect the leads yet. Once you have the tank loose, position it so you can read the labels next to the connectors. One is input and the other is output. Label the leads so you know which is which as there is no standard color code. OK, now you can disconnect them.

Grab the new tank and remove ALL the foam packing materials. Put the old tank to one side and plug in the new one connecting the leads that you labelled just a few moments ago to the corresponding places. You did label them, right? Rest the tank somewhere where the springs are not fouling anything and try it out. If all is good you can proceed with the reinstallation. Do take care with combos as the speaker magnet will try to wrestle it out of your hands and no-one will take a scratched tank back.



amp repair, amp tech, amp mods, valve amplifier repair, effects repair,guitar amplifier repair,vintage amp repair, bass amp repair