Does your new offices have a light with a dimmer switch? If so, try plugging the amp into another outlet.
I have a slightly different problem, where I have to use a noise gate in my axe fx presets because my pickups pick up the hum from the dimmer switch. It took me years to discover this source of hum, because I always leave the lights on full in my office 
Doesn’t appear to be!
No dimmers! I made sure of that. I picked up a power conditioner / fillter so we’ll see if that helps with other types of periodic noise which I think might be power line related. But with this amp the hum is constant so I suspect it is something with this amp specifically.
I’m not sure what model you have, but poking around Google a bit suggests that the Carerra, at least, has a tube-driven reverb and FX loop, and I suspect if one of their amps does, the rest do. That said, if you already tried swapping out every single 12AX7, that would sort of imply that the tube in the reverb circuit isn’t the culprit…
If you ruled out preamp tubes, a tech might be best. It’s more than likely bad power, a issue with the caps, or a ground issue somewhere. That’s a wide spectrum. A good tech can track the problem down.
I would assume this is similar but that’s over my pay grade! If it’s a tube it’s not one of the ones I swapped. Maybe power tube?
Oz Noy just left, he used our JCM800 and a couple pedals and it sounded great, so off to a shop with the Cornford.
I’d say most likely not, but if you’ve owned the amp more than a year or two, played it a couple times a week, and haven’t swapped tubes, you’re probably due for a new set anyway, so you lose nothing by trying, I guess…
And yeah, I guess we should keep you poring over slo-mo picking videos, and not amp schematics! 
I think it has residual AC ripple on the supply, which means hum in the output of the amp
To get the ac ripple filtered usually a choke filter is installed
The jcm800 has the choke factory installed,thats’s why it doesn’t hum as much
Its not a difficult task to install one on the conford,but i suggest you to leave that to an experienced tech,there is electrical hazard danger 
A single preamp tube can really lower or raise the noise floor of an amp. The issue with lowering it could affect the amount of gain on tap, depending on the kind of tube you’re using.
It could also be just a noisy tube. Maybe you could swap it for a similar gain level tube and see.
Are you using NOS tubes or current production?
I’m betting that Cornford uses a tube for the reverb.
The issue with new production tubes is that they often are gainier than they should be. They also aren’t as robust as NOS tubes, and are more likely to degrade and get noisier quickly.
If you’ve got a Cornford, you should try some of the lower cost NOS preamp tube offerings still out there. There are decent 12at7 options that have a ton of character, and almost as much gain, as a 12ax7 without breaking the bank.
What model Cornford do you have? The Cornford Hurricane appears to have the reverb tube in the second preamp tube next to the power tubes:
Also, using a lower gain preamp tube in your reverb spot should not affect the overall preamp gain of the circuit, though it could shift the way the reverb sounds.
Ok, so I guess we’ll see what the tech says.
V5 is your reverb tube. I would try swapping that one alone and see if it helps, but you may need to get a lower gain tube. To my ears, off the shelf production tubes these days are often gainy with a crappy character. A nice NOS 12at7 may tame the noise in your reverb.
http://el34world.com/charts/Schematics/files/cornford/Cornford%20Hellcat.pdf
Very cool guys! Way over my head with all this but interesting nonetheless.
It’s back, and it sounds great. I used Main Drag Music in Williamsburg. The tech is Pat who I haven’t used before but is a super nice dude and really seemed to know his stuff.
The power tubes were cooked, as in actually blackened, so he replaced with new EL84s. Then he moved preamp tubes around for lowest noise and replaced the first one with one of his own that he liked better. He kept the others.
The hum is mostly gone unless you really crank the knobs. It was probably always present to some small extent given its high gain, and I just didn’t notice until things started to go bad and it became loud enough to leak into our mics. It’s now back down to a level where it won’t cause a problem and I probably wouldn’t have noticed.
Glad you got it sorted out!
