Marshall thor (super lead simulator) problem

[dot1q]

Hi!
I'm new for this forum,
I would want to ask a question about  the THOR marshall superlead simulator.
I found the pcb and the electric diagram of the circuit in the site http://www.runoffgroove.com/thor.html
I put like transistor Q2 a BF245c instead j201 (because I can't find it)
I have regulated the drain's voltage...I  observed that the circuit works well for little time, then the sound (distortion) becomes thin and weak..
I observed also that the circuit doesn't work well, when the switch (bright) is connected to pcb...
I  found the possible failure, I 've replaced the IC tl071 with another new ; the circuit worked well, for a little , but then the circuit does the same lack. Where's the problem ? 
Can someone help me Please!!
Sorry for my bad english. (I'm a Italian boy) 

Thanks to all!!

[dot1q]

my values are:
Q1(2n5457)
g: 0v
s: 0.46v
d: 6.4v

Q2(2n5457)
g: 0v
s: 2.65v
d: 4.5v

Q3(2n5457)
g: 2.21v
s: 4.8v
d: 8.79v

Q4(2n5457)
g: 0v
s: 0.58v
d: 4.21v

IC1(tl071)
1: 0.69v
2 :6.42v
3: 3.76v
4: 0v
5: 0.68v
6: 8.16v
7: 8.76v
8: 0

[Ardric]

Pin 2 on the TL071, the negative input, should be at the same DC voltage as pin 6, the output.  There's probably a wiring problem.

The PCB layout at ROG needs two jumper wires installed on the component side of the board.  They're shown as red lines on the part placement diagram.  Did you possibly forget these?

[dot1q]

thanks for your answer!
no, i put the jumpers 

The circuit has worked since I put the switch 1 (bright) on the circuit... is it possibile cause? 
other solutions??
Thanks!!

[dot1q]

...when the circuit was working well, the IC1(tl071) values were
1: 0.18v
2: 4.41v
3: 4.02v
4: 0v
5: 0.18v
6: 4.41v
7: 8.83v
8: n.c
What can be happened?

[Meanderthal]

 Could be when you installed the switch you knocked loose a teeny weeny solder bridge...