The things being discussed are 2 seperate type problems. The Vibrating hum if bad enough, can be heard without headphones. The PT will vibrate or make a buzz type sound. Most PTs will have a very slight same type thing happening, but its normal. Its the PT that is excessive that is the problem. And pretty sure some od the PTs don't even have a hum band.
Some PTs you may not feel,hear or notice anything,some very slight,which is normal. Its when you get one that is just way too much,that it vibrates the chassis,and can be picked up and heard through the amp,which makes it even worse.
The other type they are talking about is a hum, because of the placement of the transformers or fields interacting. And the headphone test in comparison, would be if you had a strat and single coil pickups, you can turn a different angle and the hum gets worse or is less. Thats what you do with the transformer,you turn it till you hear the least hum or no hum at all.
So 2 different things here. Back in about 68 Marshall turned their output transformer, one of the ways to tell if its a stock amp, which way the bells are facing.
Since we are on the subject, i answered another question on another forum a few minutes ago. They had a buzzy recto tube. Even made a clip of it. I was suprised to see many pople have all kinds of different answers,some from people that were tube guys.
I would have thought that they should have seen this many times over. Or to me it seems a common thing. Some recto tubes will have a slight mecanical rattle or buzz, nothing wrong with them other than having the annoying buzz.
This too can be picked up,and heard through the amp. Most all of these tubes that do this, you can place your wood dowel on the top of the tube, or your finger [just don't get burned] and the noise will stop. Like loose parts inside the tube.
Even a tube dampener can sometimes cure the noise. The tube may be fine other than the noise,and never have a problem.
Seems as some tubes wear, they get very rattley or noisey,even power tubes can make low rumbles,and be microphonic. And even some NEW tubes can be the same. I have heard the noise from about every recto tube type that is used in amps. NOS to whatever.
But its always nice to have one that doesn't make the buzz rattly noise..
Just saying, sometimes you have to figure out where and what the noise is,and what and where its coming from or causing it.
And a lost note, sometimes a noisey or vibrating PT, you can mount the PT on rubber gasket, or rubber washers, it can help keep down the vibrations getting picked up on the chassis,than a PT that is mounted solid on the chassis.
