diy univibe no sound

[R.G.]

RG my power supply is not working. i am using a different 19v power supply. i dont know if it will give the wrong readings.

It's OK. I can look at the critical things, adjusting for what 19V on the power supply might mean. As an aside, the absolute power supply voltage doesn't matter a whole lot for the univibe circuit, as long as it's within 15-20V. When I did my univibe update/clone boards, I put in 7815 or 7818 voltage regulator chips for the low impedance more than for a fixed power supply voltage.

Q1 base 1.299 collector 2.093 emitter 920 

Base is 1.299, emitter is 0.92, difference is 0.36, base more positive. This is probably OK. We'll see later in this note that it really is OK. The first transistor of the univibe has a quirk that the meter's resistance makes it look lower than it should be.
The collector is higher than the base, so this thing is probably working as an amplifier.

Q2 base 2.097 collector 3.72 emmiter 1.503   

Base is 2.097-1.503 = 0.594V higher than the base. This is good - it's a normal voltage for an NPN base-emitter in active operation. The collector is higher than the base, so this transistor is operating as an amplifier.
Even better, the collector of Q1 and the base of Q2 are showing the same voltage (within measurement tolerance) so the circuit actuals match what we expect from the schematic.

Q3 base 3.72 collector 11.14 emmiter 3.102

Again, base higher than emitter by one silicon diode drop (0.5-0.7V) so this transistor is active. The collector is higher than the base, so it's in the amplifying region of operation.

The only criticism I have of this one is that the emitter is at 3.102V, but you show the collector at 11.14V.  This is suspicious, and especially so since you're seeing not-much-effect. Here's why.
The emitter voltage of 3.102 is flowing through a 3.9K resistor and a 1.2K resistor. That's a total of 5.1K ohms. Ohm's Law tells us that 3.102V through a 5100 ohm resistor is 608uA of current. This is the sum of the collector current and base current. The base current is 1/50 to 1/100 of this. For this quick and dirty purpose, we can assume the base current is 6uA, and call the collector current 602uA.
This current has to flow through the collector resistor. This resistor is 4700 ohms, so the voltage across it is 602uA*4700 ohms, or 2.892V. This has to be subtracted from the power supply voltage of 19V. I would expect the collector to be at 19-2.892 = 16.17V. Instead, it's five volts lower.
So something is wrong here. Either the power supply that is actually getting to this transistor is down at about 14V, or something else is siphoning off current, not the transistor as it should be.
This matches the complaint of poor effect. If the signals at collector and emitter of Q3 are not equal and opposite reasonably, then you don't get much effect.

If I were doing this, at this point I would:
1. measure the voltage at both ends of the 4700 ohm collector resistor. You would expect the collector end to be 11V, per your measurements. The other is probably 14V. If it's really 19V, then the "4700 ohm" collector resistor can't really be 4700 ohms.
2. remove the two 1uF capacitors, one from collector of q3 and one from the emitter; measure the DC voltage on base, collector, and emitter of Q3 again, as well as the power supply at the top of the 4700 resistor.

Something is still hosed in this, and it could account for your problems now.

i took them out of circuit and read them with a peak dca55. i dont know if the readings are any good for you.

[willienillie]

19VDC power supply is going through a diode drop and a couple R-C filter stages, before it feeds the Q3 collector resistor.

[R.G.]

Maybe so. Depends on where he spiced in this other power supply, I guess.

[willienillie]

Maybe so. Depends on where he spiced in this other power supply, I guess.

Yeah I made assumptions.

[R.G.]

Me too. Let's see if plen will tell us the voltages on the collectors of the phase transistors. That tells us the voltage getting through to the preamp.

[plen]

rg is that Q6 and Q7

[R.G.]

Q6 and Q7 should do fine. The pairs of Q4/5, Q6/7, and Q8/9 all have one of the collectors tied to the power supply voltage. Yours were all biased OK as I remember, so any one of those pairs will do the trick of telling us what the actual power supply voltage leading to the Q1/2/3 preamp devices.

[plen]

Q6 14.76 Q7 11.00

[Marcos - Munky]

Check your voltages again. Before you said the voltages are 15.6V for Q6 and 11.6V or Q7. Are you sure you checked the collector and not the emitter?

base collector emitter  Q1  .065  .638  .001  Q2 .636  .077 .072  Q3 15.56 .001 .001  Q4 5.00 15.56 4.57  Q5 4.57 11.49 3.95  Q6 4.92 15.56 4.49  Q7 4.49 11.60 3.87  Q8 5.24 15.56 5.29  Q9 4.82 11.45 4.20  Q10 6.30 15.56 5.79  Q11 920 18.56 9.90  Q12 9.40 18.56 9.90  Q13 2.993 12.94 2.358   diode d3 19.30   big capacitors 18.56  17.04  15.56

[plen]

marcus - munky i have edited my last post. Q6 14.76  Q7 11.00   my power supply is broken. i have been using different ones that i have laying around. maybe this is why i am getting different readings. i have sent away for a 15vdc 1a power supply i hope that helps.

[Marcos - Munky]

The thing is if you keep changing the power supply each time you do voltage measurements, we can't know for sure what's really happening.

[plen]

marcos sometimes if i change a resistor or something i will try different power supplys to see if the univibe will work. different power supply do different things to the univibe. some times i forget to put the same power supply back although most of the time it is the same one. the last readings i gave you i read the wrong pin. most times im asked for readings it is 3am or 4am and i dont have a clear head.

thanks.

[R.G.]

As Marcos notes, quit changing the power supply when you feed us info. Or at least always include all transistor pin voltages from all of them when you send us voltages. It messes up our reasoning and we can't help you.

In addition, the univibe is not terribly sensitive to power supply voltages. The basic circuit works from power supplies from about 15Vdc up to about 20Vdc. So pick one power supply in that range and use it for testing. Changing power supplies around will confuse you as well as us.

[Marcos - Munky]

Then do the measuremens when you have a clear head, and with just only power supply. If it works with one, it should work with all of them, if the transistors are biased correctly.

See,

Q6 and Q7 should do fine. The pairs of Q4/5, Q6/7, and Q8/9 all have one of the collectors tied to the power supply voltage. Yours were all biased OK as I remember, so any one of those pairs will do the trick of telling us what the actual power supply voltage leading to the Q1/2/3 preamp devices.

RG is trying to compare the voltages on Q1/2/3 with the voltages on Q6/7, to check what should be the correct voltage on Q1/2/3. Different power supplies rated for the same voltage usually ends up giving different output voltages, and even worse, the same power supply may output different voltages based on how much current is being drawn (unless they're regulated). So if you give a reading for Q1/2/3 using one power supply and a reading for Q6/7 using a different power supply, then we can't compare them at all, and will lead us to think on "why this point have lower voltage than the other one if it was supposed to be the other way" and look for problems that doesn't exist.

[plen]

marcos i mentioned the different power supplys to RG a week ago and got this reply.  Quote from: plen on April 16, 2020, 09:54:32 PM

    RG my power supply is not working. i am using a different 19v power supply. i dont know if it will give the wrong readings.

It's OK. I can look at the critical things, adjusting for what 19V on the power supply might mean. As an aside, the absolute power supply voltage doesn't matter a whole lot for the univibe circuit, as long as it's within 15-20V. When I did my univibe update/clone boards, I put in 7815 or 7818 voltage regulator chips for the low impedance more than for a fixed power supply voltage.   the 2 univibes my son and i built 6 years ago didnt work with all the power supplys  we tried them with then. so they dont work with all power supplys in the 15v to 20v region.