Hum query with a Rivera R55

Kalimna

Greetings folks,
Ordinarily, I'd maybe ask about this here before taking in to a shop, but I wonder if it might be something I can try simple things on first.
I have a Rivera R55 head (conversion from a combo) that I bought a couple of years ago and has remained in a cupboard since. I am fairly certain there were no issues at the time.
Plugging into a cab a week or so ago, I noticed significant hum whenever the reverb (which sounded glorious apart from the hum) was turned up beyond 1-2, in other words - when the reverb was audible. There were no obvious issues elsewhere on the amp, though getting to grips with the channel settings not straightforward. 
A quick look around the back, and the phono-cable from reverb tank to/from amp chassis seemed to be very long and winding - and in the absence of taking apart completely, I wondered if this might be the issue? In other words, would it be reasonable to shorten these wires in the first instance?
Thanks for any advice,

Adam

ICBM

Possibly worth trying, since it has no penalty at all - but not the most likely cause, especially if the problem wasn't there before.

First, have you tried the amp in different positions or rooms? Reverb hum is often picked up from an external source.

Second, it could simply be a bad contact in the ground connection at one end of the tank, or the ones in the amp. Try wiggling the phono jacks.

A combo to head conversion can often be a problem because it brings the tank much closer to the amp's PT - at the least, the tank needs to be oriented so the output end is as far from the PT as possible - but this would have been something that showed up straight away. Likewise a problem with a ground loop via the tank, which are sometimes designed to be grounded at one end only, so replacing the tank with one that's grounded at both ends can cause trouble.

Kalimna

Thanks (once again, ICBM) - I shall have another look and a wiggle of the connectors. If there's no improvement, I shall drop it into Strung Out when that becomes possible again, as the amp sounds rather nice - but then I seem to recall you are a fan of Rivera anyway...
I think room location is unlikely in this instance to be a problem, but I shall try in a different location.

Cheers,
Adam