There is a simple way to do this using an incandescent light bulb. You remove all tubes and put the light bulb in series with the AC power and turn it on.
The light bulb will light up, which means most of the power is being dissipated by the bulb because the caps are likely shorted. However, if they need to 'form up', the bulb prevents them from heating up by limiting the current. If the bulb goes out the caps are formed up and OK.
Time-honored technique BTW; but if this is an amplifier you intend to really play a lot don't screw around- just change out every filter cap in sight... If there is a selenium rectifier change that out too.
The light bulb will light up, which means most of the power is being dissipated by the bulb because the caps are likely shorted. However, if they need to 'form up', the bulb prevents them from heating up by limiting the current. If the bulb goes out the caps are formed up and OK.
Time-honored technique BTW; but if this is an amplifier you intend to really play a lot don't screw around- just change out every filter cap in sight... If there is a selenium rectifier change that out too.