univibe neovibe GGG problem, bulb does not glow

[hamedbb]

hi I making a univibe from GGG schematic and pcb I etched. well I soldered everything and now it doesnt work. I checked solderings and  parts to be correct but voltages of Q11,Q12 and Q13 are not right and I cant realize why? any ideas?
votages:
Q E B C
1 1.01  1.4 1.98
2 1.06 1.97 4.38
3 3.78 4.4 11.61
4 4.43 4.83 15.5
5 3.83 4.43 15.5
6 4.57 4.96 15.53
7 3.97 4.57 11.3
8 10.7 11.3 15.53
9 10.01 10.7 10.2
10 6.5 7.03 15.5
11 7to13 6to11 18
12 7to13 6to11 18
13 2.5to4 3to5 18
i think Q9 is not right too

[Kevin Mitchell]

Your measurements don't make sense in some places. Q11 pin 1 should have the same voltage as Q12 pin 2.

Power supply voltages look good.
Any oscillation of the bulb?
Any signal passing through?
Did you use the recommended parts in the bill of materials or did you choose any alternatives?

Think of it as two circuits on one board. If you have no signal there is something wrong in the signal chain (Q1 through Q10). This section is where an audio probe will aid you tremendously.
If the lamp isn't pulsing then you have a problem between Q11 through Q13.

A common mistake that can cause problems in both sections is incorrect or bad wiring. I only say this because there aren't any obvious shorts in your readings which would be the first thing to inspect.

Share photos of your work if you can. Another set of eyes is always good when things aren't clear.

[hamedbb]

Your measurements don't make sense in some places. Q11 pin 1 should have the same voltage as Q12 pin 2.

Power supply voltages look good.
Any oscillation of the bulb?
Any signal passing through?
Did you use the recommended parts in the bill of materials or did you choose any alternatives?

Think of it as two circuits on one board. If you have no signal there is something wrong in the signal chain (Q1 through Q10). This section is where an audio probe will aid you tremendously.
If the lamp isn't pulsing then you have a problem between Q11 through Q13.

A common mistake that can cause problems in both sections is incorrect or bad wiring. I only say this because there aren't any obvious shorts in your readings which would be the first thing to inspect.

Share photos of your work if you can. Another set of eyes is always good when things aren't clear.

well i checked some voltages again and Q1 to Q10 are ok. signal passes through the circuit and vol knob works but no effect, no bulb light and nothing. one other thing, in the GGG pdf file there are some voltage for debugging and between R40 and R41 it must be 11.7 and in my curcuit its 10.7. all voltages of Q11 to Q13 are not stable except for collectors.

[hamedbb]

for Q1to12 i used bc545 and for q13 2n4401. and q13 gets hot

[Kevin Mitchell]

Okay looks like you were mindful of the pin changes on your substitution but I'm unsure if these will function 1:1 as the suggested general-purpose NPNs. 2N5088 or 2n3904 are suggested for Q11 & Q12.

Collectors should be stable as they're tied to +18v. You will see unstable voltages elsewhere as this is the LFO circuit (Low Frequency Oscillator) that generates a sine wave to pulse the lamp.

As for the 11.7v note. This node is supplied voltage via a resistor divider. Let's calculate.
R39 = 3300 ohms
R41 = 4700 ohms
Supply voltage = 18.
Vout is (18*4700)/(3300+4700) = 10.575. Will not be perfect due to the 5% carbon film resistor tolerance & not dead-on supply voltage.
So your observation is more correct than the notes on the schematic.

Have you possibly burned out the drive transistor/Q13? Try a 2N3904 or a higher gain transistor.

You also need to isolate the LDRs/Lamp or else the LDRs are stuck at an "on" state due to room lighting.
To verify the phase shifting for the signal path, any action when you wave your hand over the LDRs?

[hamedbb]

Okay looks like you were mindful of the pin changes on your substitution but I'm unsure if these will function 1:1 as the suggested general-purpose NPNs. 2N5088 or 2n3904 are suggested for Q11 & Q12.

Collectors should be stable as they're tied to +18v. You will see unstable voltages elsewhere as this is the LFO circuit (Low Frequency Oscillator) that generates a sine wave to pulse the lamp.

As for the 11.7v note. This node is supplied voltage via a resistor divider. Let's calculate.
R39 = 3300 ohms
R41 = 4700 ohms
Supply voltage = 18.
Vout is (18*4700)/(3300+4700) = 10.575. Will not be perfect due to the 5% carbon film resistor tolerance & not dead-on supply voltage.
So your observation is more correct than the notes on the schematic.

Have you possibly burned out the drive transistor/Q13? Try a 2N3904 or a higher gain transistor.

You also need to isolate the LDRs/Lamp or else the LDRs are stuck at an "on" state due to room lighting.
To verify the phase shifting for the signal path, any action when you wave your hand over the LDRs?

well I desoldered Q13 (2n4401) and it was ok. well  i isolated ldrs and bulb barely glows(it glows dimly) in its (and with pot set to zero Ohm) bc546 is almost identical with 2n3904 in spec only with higher voltages and the ggg says NPNs are not critical. do you think I should replace them with 3904 or 5088?

[Kevin Mitchell]

What is the DC rating of the bulb you're using? Too high and it won't burn so bright. I've seen 5v to 12v here with no trouble.
Do you get any response on the bulb when adjusting speed, depth or the the trimpot? Diming your room lights may help show more details of the behavior.

And the hand over the LDR trick was so you can listen for phase shifting without the LFO. That way you know for sure half of the circuit is well.

Also, this is in the build notes.

You may have to increase the 47K resistor from the base of the driver transistor to ground (Q50). Some transistors
like this at 100K-330K, and some like it open. The right point to hit is where the bulb is glowing dimly orange when
the amplitude pot is all the way down. Twiddle the emitter resistor and base-to-ground resistors until the board
mounted pot lets you dial in the proper bias.

[anotherjim]

Kevin is giving good guidance.
The small silicon BJT transistors in modern production are generally mid specification, but older production can contain odd examples that are weak. For example, newish 2N3904 often has a gain hfe of at least 220 but I've found the odd one in old stock that tested at 40.
Does your DMM have transistor test sockets?

[hamedbb]

What is the DC rating of the bulb you're using? Too high and it won't burn so bright. I've seen 5v to 12v here with no trouble.
Do you get any response on the bulb when adjusting speed, depth or the the trimpot? Diming your room lights may help show more details of the behavior.

And the hand over the LDR trick was so you can listen for phase shifting without the LFO. That way you know for sure half of the circuit is well.

Also, this is in the build notes.

You may have to increase the 47K resistor from the base of the driver transistor to ground (Q50). Some transistors
like this at 100K-330K, and some like it open. The right point to hit is where the bulb is glowing dimly orange when
the amplitude pot is all the way down. Twiddle the emitter resistor and base-to-ground resistors until the board
mounted pot lets you dial in the proper bias.

Kevin is giving good guidance.
The small silicon BJT transistors in modern production are generally mid specification, but older production can contain odd examples that are weak. For example, newish 2N3904 often has a gain hfe of at least 220 but I've found the odd one in old stock that tested at 40.
Does your DMM have transistor test sockets?

well bulb dc rating is 12v. its fully responsing to all control knobs. i changed Q13 to 2n3904 with higher hfe(around 350) and bulb gest a little lighter. but not light enough. i changed R50 to a 200k pot and set it to  max change light just a little

[hamedbb]

well i changed the bulb and it works but there is a cracking sound after a while in the sound. i think its because of current Q13 cant handle and it gets hot. I think I must test some NPN or maybe a TO220 package.

[Kevin Mitchell]

well i changed the bulb and it works but there is a cracking sound after a while in the sound. i think its because of current Q13 cant handle and it gets hot. I think I must test some NPN or maybe a TO220 package.

Popping or clicking would suggest the need for more decoupling - raising the 1000uF caps.
Cracking is likely a connection issue - especially if it comes and goes. This would be within the signal path & not the LFO circuit with the hot transistor (which will likely burn out one day). A darlington NPN would be a better fit. I used MPSW45 in a couple and worked great.

[antonis]

I think that Q13 issue relies on bulb's power (Wattage)..

[Kevin Mitchell]

I think that Q13 issue relies on bulb's power (Wattage)..

Pretty sure you're right. Let's try to get a rough figure a for a max rating.
What is it... W=V*A?
So in my case with a 12v lamp @ 60ma it would be...
12*0.06 = 0.72 watts
Max dissipation for 2N3904 (from tayda at least) is 0.625 watts.

Figure it would take less current to drive it as it's oscillating and never at full power. This is likely why I haven't burned a 2N3904 drive transistor yet when using those lamps.

The rating of a 2N4401 is identical to a 2N3904 which would discredit my suggestion for the swap. So I'll guess the lamp in this build is more power hungry than what I use.