DIY Univibe clone issues - lamp not lighting up

[Dotoar]

As new to this forum as I am to effect box building. Having successfully put together a few Rangemasters and fuzzboxes, I decided to give the Univibe a go. I've been following the Neo-vibe schematics as found here: http://www.geofex.com/Article_Folders/univibe/vibeupdate.pdf

Not entirely unexpectedly, I did not manage to get it going on the first try, and I have been revisiting this project several times now with no success. The issue is that I cannot get the lightbulb to work. After hours of troubleshooting I finally remade the whole LFO and lamp driver part of the circuit, just to make sure I hadn't overlooked anything but the result is still the same; no flashing light to be seen.

I've measure the three voltage points shown in that part of the circuit and the values are close enough, at least for anything to happen. When unscrewing the bulb and measuring the voltage on the supply side, it reads around 17 volts (slightly lower, but in the ballpark) and with the bulb in place, naturally the same goes for both terminals. Another thing is that when shortening the base pin of the driver transistor Q13 to ground (which constitutes the cancel switch in the original setup), the bulb lights up fully, which is the opposite of what should happen. Also, when measuring the voltages on the base and emitter on Q13, it's sort of undulating up and down which to me is a token of the LFO stage doing its job, or am I completely out to lunch there?



Would greatly appreciate if anyone more electronically gifted might have an idea of what I've missed and could point me towards any potential failures.

[antonis]

when shortening the base pin of the driver transistor Q13 to ground (which constitutes the cancel switch in the original setup), the bulb lights up fully, which is the opposite of what should happen.

Hi & Welcome..

First of all, check for proper Q13 classification (n-p-n or p-n-p)
If it indeed is n-p-n, check for proper pinout mounting..

[PRR]

From here it smells like a short near that transistor. How did you build? Perfboard? Bought a PCB? Made a PCB?

[Dotoar]

I'm using a 2N3904 for the lamp driver, as per suggested in said description. (2N5088 for the rest, and I did initially have one for Q13 as well but changed it after discovering that it didn't work, albeit obviously to no avail). I have tried several ones from the batch I ordered as well, should be noted.

From here it smells like a short near that transistor. How did you build? Perfboard? Bought a PCB? Made a PCB?

I'm doing the whole thing point-to-point on perfboard.

I'll let it rest for a while and will get back to it in due time. Further suggestions are of course welcome in the meantime.

[Big Monk]

I'm using a 2N3904 for the lamp driver, as per suggested in said description. (2N5088 for the rest, and I did initially have one for Q13 as well but changed it after discovering that it didn't work, albeit obviously to no avail). I have tried several ones from the batch I ordered as well, should be noted.

From here it smells like a short near that transistor. How did you build? Perfboard? Bought a PCB? Made a PCB?

I'm doing the whole thing point-to-point on perfboard.

I'll let it rest for a while and will get back to it in due time. Further suggestions are of course welcome in the meantime.

My suggestion would be to buy a PCB.

A UniVibe on perf for a new builder is a daunting task almost doomed to failure. There are a number of preface boards available.

[Dotoar]

My suggestion would be to buy a PCB.

A UniVibe on perf for a new builder is a daunting task almost doomed to failure. There are a number of preface boards available.

I actually did order a PCB recently as a last resort. But I've set myself the task of making this one succeed. After all, history isn't written by those who took the easy road.

[Big Monk]

My suggestion would be to buy a PCB.

A UniVibe on perf for a new builder is a daunting task almost doomed to failure. There are a number of preface boards available.

I actually did order a PCB recently as a last resort. But I've set myself the task of making this one succeed. After all, history isn't written by those who took the easy road.

True, but complex circuits built by new builders on Perf is the "hard road" x100.

Can you post some pictures of your board so far and the schematic you are using?

[Dotoar]

Can you post some pictures of your board so far and the schematic you are using?

Certainly:





Note that this is just the LFO/lamp driver part of the circuit. Also note that I'm assembling the components as I go along so the ensuing tidiness (or lack thereof) definitely isn't up to any professional standard, but the first version of this part of the board was even worse, believe it or not.

And the schematics were posted in the threadstart, but here it is in clear view for good measure:

[Dotoar]

Also note that the base resistor on Q13 was subject to some experimantation with the values, hence the twisted ends. It was originally a 47 K but as the description hinted at higher values depending on the transistor, I messed around with putting another one in series, I believe it was a 200 K. Not that it made any difference.

[Dotoar]

Revisiting this project that's been laying dormant. (I've been building other effects in the meantime, mind you, if only to gain some more confidence in my rudimentary skills). Nothing's been done since my last post so we're picking it up right where we left off. Here are some approximate voltage measures, if anyone has got any clue to where the problem may reside:



Q13:
C: 15 v
B: 4,35 v
E: 3,75 v

Q12:
C: 15,3 v
B: Oscillating between 7,8 - 9,5 v (I assume that it's supposed to somewhere around this part of the circuit)
E: Oscillating between 6,8 - 8,9 v

Q11:
C: 15,4 v
B: Oscillating between 6,4 - 8 v
E: Oscillating between 7,6 - 9,7 v

Lamp: 15,54 on one side and 15,41 on the other.

Perhaps someone has got a working Univibe or clone thereof for reference?