http://www.voxshowroom.com/uk/amp/vt30_hood.html

It seems as if the VT30 is based on Vox's "valve reactor" technology:
 
 

 

 
There are several flow charts showing the Vox Valve Reactor™ topology but I haven't found one specific to the VT30.
 
In the VT30 the "output transformer" has been replaced with Coupling Capacitor Technology™.
 
 

<my apologies in advance to the OP>
Do you think there's a whole 50 volts on the plate of that 12ax7?
Ah, the ubiquitous Flux Capacitor™, right up there with Unobtainium™.
Don't look now but this:
true tube push/pull power amp
trumps this:
class-A, class-AB
every time; at least in my experience.
There are at least a hundred reasons a Vox AC30 sounds like a Vox AC30.
The Cathode biased output stage NOT being, IMHO, the "main" reason.
You can call it class-A, if you like, its STILL a push/pull amplifier...
</my apologies in advance to the OP>
 
Tom

 
So much for high voltages and large power supply caps.
 
Here's something that may apply :

 
From :  http://www.seymourduncan.com/forum/showthread.php?201710-Vox-VT30-LED-under-the-tube/page2

Thanks to all of you for your replies.  I am definately no tech when it comes to this stuff.  I can solder xlr cables and change a tube but that's about it. I will turn off and unplug power and take the brain out, replace the tube and make sure I have good connections with the connectors.  Then I will reassemble and power it up.  If the hum is still there, I will try disconnecting the headphone lead as suggested in the link I posted earlier.  It that doesn't do it, I think this unit is dead and I will not be putting any more money into repair.  
 
At that point, I might look for a tube head that might be used with the cabinet.  
What is a bummer is that this amp really sounded good before the hum happened.  It was clean and could crank up really nicely.  I am just getting into micing my leads and then this happened.  :)
 

My money is on a bad capacitor in the power amp. Likely a 2 cent component. Have a really close look at the electrolytic caps. The little cans that are soldered onto the board. One is likely bad or has a bad connection to the board. 
 
Merry Christmas

Is that 12AX7 running low plate voltage ("starved plate") operation?

ampfixer
My money is on a bad capacitor in the power amp. Likely a 2 cent component. Have a really close look at the electrolytic caps. The little cans that are soldered onto the board. One is likely bad or has a bad connection to the board. 
 
Merry Christmas

Will check that.  Thanks.

fireberd
Is that 12AX7 running low plate voltage ("starved plate") operation?

Hi fireberd, I am sorry but I don't know the answer to your question.  Where can I find out?