Killed my Neovibe while biasing. Advice requested

[andrew_k]

[edit]Read my second post before wasting your time going through this long post. 

I was so happy when I first built this thing and it fired right up... months later, I seem to have killed it while adjusting the 500R lamp trimpot. Yes, I have gone through pages of neovibe debug threads trying to find a solution; I really didn't want to have to create another one 

Lamp driver is 2N3904, all other 2N5089. This circuit was complete and working without issue on a previous, crappy power supply. That power supply has since died and I'm now running it off 2 lines from my BBE supa charger in series.

Power supply = 21.5v DC
DB102 + = 20.1v

I've replaced the bulb (I blew the original one while tweaking the trimpot, have only got 1.5v/9v/12v 100mA bulbs now), replaced the 2N3904 (multiple times to be sure) and I'm getting some odd voltages at the lamp socket that lead me to believe I've fried something; hopefully the trimpot...

Primary symptom - bulb not vibin or lighting up'. With the depth at zero and the trimpot at halfway, I get a voltage reading of 20.1v on the left bulb terminal and 0v on the right. Sticking one probe in each side of the bulb socket gives a reading of 19.8v. I might be wrong, but this appears to be far to high of a voltage to be feeding the bulb. When it was working, I think full swing (depth at full) when reading from the bulb socket was 0v to just over 9v.

Here are the voltages:

supply = 21.5v DC

DB102 + = 20.1v

7815:
I = 20.1v
G = 0v
O = 15v

Q1:
C = 2.1
B = 1.38
E = 1.0

Q2:
C = 4.36
B = 2.1
E = 1.57

Q3:
C = 11.09
B = 4.36
E = 3.75

Q4:
C = 14.98
B = 4.76
E = 4.36

Q5
C = 11.22
B = 4.36
E = 3.75

Q6
C = 14.98
B = 4.77
E = 4.37

Q7
C = 11.22
B = 4.37
E = 3.76

Q8
C = 14.98
B = 4.73
E = 4.33

Q9
C = 11.27
B = 4.33
E = 3.72

Q10
C = 14.97
B = 5.97
E = 5.46

Q11
C = 20.1
B = 8.6 - 10.1 (11.8v measured on far side of 2.2m resistor)
E = 10.1 - 12.4 (couldn't get stable reading)

Q12
C = 20.1
B = 10.6 - 12.4
E = 9.5 - 11.8

Q13
C = 0
B = 0
E = 0

Any assistance is very, very welcome 

[andrew_k]

AHA! 

I found one of the large 1.5v 25mA bulbs from SmallBear in my parts drawers, and that fired up fine! So it's the 100mA bulb I've used that stops it from working. The large bulb and socket won't fit in my enclosure, so I still need to get more of the 'grain of wheat' style bulbs.
Shame none of the local electronics places stock a suitable bulb, looks like I'll order a pile of them from SmallBear so I don't have to go through this again.

[bluesdevil]

Well, that's good news! I blew a bulb on my build when biasing too..... I think I then replaced the trimmer with a bigger value or replaced a connecting resistor to make it harder to burn up bulb when adjusting.