These amps always have a certain level of noise / gain hiss to them at around 2khz.
Does the volume control in either channel make a difference in the level of hiss being heard?

In terms of the reverb hum that is most likely due to the pan having been taken out of the amp and reinstalled the wrong way .
The end of the tank with the connection marked output can not be the end closest to the power transformer which is on the right side when viewing the open chassis from the front of the amp.