VOX V15 – Under The Hood
So, we’ve ascertained that there is power in to the VOX V15 and some valve lights but nothing audible except for a loud buzz. Time to take it apart and see what we have.
With the amp still plugged in and the mains switch turned off, we are earthed and so can begin poking about. Loosening the four screws as shown means we can take the main board away from the cab and turn it over:
We can see 5 valves (one of which is a bit wonkily seated), what I take to be transformers, the circuit board printed on the back (nice touch!) and a mass of cobwebs:
Removing the cover from the leftmost valve in the picture – I’m guessing it’s a heat shield as it’s right next to the transformer – I switch on the amplifier and wait to see what happens.
The two larger valves and the two leftmost ones light up immediately, the one in the middle with the milky appearance doesn’t – looking closer we can see a hairline crack in the top. Uncle Google pointed me to this page which states:
- Valves can be quite dramatic if they blow with loud crackling noises and a very bright glow from the valve as the valve consumes itself.
- A valve can also blow with little or no visible effect.
- Sometimes, if the vacuum in the valve is lost through tiny hairline cracks, you will see that the silver coating on the inside top of the valve will disappear or go clear.
I can’t identify *anywhere* what kind of valves are recommended and so I created a thread in the illustrious TDPRI forum for advice. Within 20 minutes I’ve got the following:
3 x 12AX7 and 2 x EL84 are what you need. This could very well be the source of the problems, but like anything in life there are no guarantees. Good luck with the resurrection!
1 – centre tap
2 – red lead from winding to V4 tube
3 – blue lead from winding to V5 tube