Testing a Reverb Tank with an Ohm Meter
If the reverb in your amplifier no longer works and you suspect the reverb tank itself is the issue, you can test the tank with an ohmmeter by doing the following.
Disconnect your reverb cables from the amplifier's chassis. Check the resistance of the reverb tank's output using an ohmmeter. To do this, put your ohmmeter leads across the tip and shield of the reverb tank’s return cable (the shielded cable). For most MESA amps with tube reverb circuits, the reading at the shielded cable's jack will be approximately 200Ω. Leaving a lead on the shield of the return cable, move the other lead to the tip of the input cable. When you read the impedance of the input (the thinner, unshielded RCA cable), the reading will be approximately 1Ω. If either point reads open (.000) the tank is at fault. This procedure not only checks the resistance of the transducers inside the tank but also confirms the common ground/shield connection that is made through the metal of the tank.
*Note: For Reverb Units that are IC driven, approximately 28 ohms is the input resistance & 220 ohms the output resistance (this applies to F-Series, Nomads, Rectoverb 50 both Series I & II, and Road King Series I amps).
Testing a Reverb Cable with an Ohm Meter
You can also check reverb cables using an ohm meter. The 2KΩ setting or continuity test setting works best. If you touch the probes/leads together, you get an open reading (.000). Touch one lead to the tip of one end of the cable and the other lead to the tip at the other end. You should get an open reading (once again .000). If your meter has a continuity test setting and you set your meter to that function, it should beep. Do the same test between the shell/return terminals of the RCA plug to see if you have continuity there.