3AX31B - EQD Spires Green Channel

[antonis]

That said, I presume you get -3.7V (negative) readings..

Not bad but they could be a bit lower (-4.5V ideally)..
Try 39k for R4 & 4k7 for R6..

Of course, you may retain Collector resistors values and alter feedback bias resistor values..
e.g. for Q1, R3 should be about h_FE times R4..

[ElectricDruid]

This is how I have it configured. 

I'm assuming from that schematic that Vcc is +9V, because you're *still* not telling us clearly what you've done or haven't done. Ground is at the bottom so that's clear, at least.

In which case, you've got a lot of PNP transistors reverse-biased in a circuit designed for NPNs. So your biasing voltages are correct (in the sense that what you measured is what you've got), but completely wrong for the transistors you're using.

[duck_arse]

.... and, if as shown and positive ground, both electros are backwards.

[idsnowdog]

This is how I have it configured. 

I'm assuming from that schematic that Vcc is +9V, because you're *still* not telling us clearly what you've done or haven't done. Ground is at the bottom so that's clear, at least.

No you are *still* hung up on the schematic symbols when I already told you that I have reversed the +/- leads and that the circuit does work.  It's not like the circuit magically started working just by changing the symbols on the schematic.  I asked for resistor values to start with.  I didn't ask anyone to critique the physical layout of my breadboard or to diagnose noise issues.

This isn't the first time I have used PNPs.  I have converted between NPN/PNP many times without problems because I knew the bias scheme and the resistor values were at least in the ballpark.  I regularly go to alltransistors.com and check for compatible transistors.  I can change si to ge and NPN to PNP in the search criteria and get a list of compatible substitutes. The difference this time is the bias scheme was completely
new to me, the documentation for the transistor was lacking, and the stock resistor values for the circuit were so far out of whack that I didn't know where to start. 

Biasing a transistor is little different than adjusting timing and carburation of an engine.  Get it right and things are nice and quiet.  Get it wrong it adds to the inherent noise of an unshielded circuit on a breadboard where everything is an antennae.

I also don't see the point of quibbling over whether the voltage at the collector reads -4.7v or +4.7v when all I need to do is reverse the leads on my multimeter.  It's not like it reads 12v one direction and 3v the other direction.   

[idsnowdog]

Here's how I resolved the bias issue. 
1. I looked up transistor biasing and I saw that the bias method is called collector-to-base feedback.  I hadn't used that before.  That led me to this website https://www.guitarscience.net/calcs/cecb.htm .  This gave me a ballpark for the resistor values.
2.  I spent hours trying different resistor values and recording the voltage at the collector.  What I noticed was Q1 and Q2 were too interdependent to allow me to zero in on a specific value.
3.  Instead of using the 100 hfe average in the online calculator I used the actual hfe values of both transistors that I got from my transistor tester.  This allowed me to find collector and feedback values that worked for both transistors.
4.  After playing for an hour I noticed that the transistors degraded when they got hot.  I already knew this was an issue and it was skewing my measurements.  So I looked for methods to mitigate temperature drift.  I found this site where they were talking about using a germanium diode to stabilize the transistors.  https://web.archive.org/web/20090122112519/http://www.geocities.com/SunsetStrip/Studio/2987/britface.html .  After adding 1N34As between the base and emitter of Q1 and Q2 the temperature sensitivity lessened and I could now change resistor values to fine tune voltage without skewing the values on either transistor.  Noise also decreased. 

[PRR]

> Q1 and Q2 were too interdependent to allow me to zero in on a specific value.

How? They are not DC-coupled. Combined with your remarks on breadboard, I wonder if it is oscillating.

[antonis]

No you are *still* hung up on the schematic symbols when I already told you that I have reversed the +/- leads and that the circuit does work.  It's not like the circuit magically started working just by changing the symbols on the schematic.  I asked for resistor values to start with.  I didn't ask anyone to critique the physical layout of my breadboard or to diagnose noise issues.

Don't get me wrong but I think WE try to help you and not YOU try to help us..!!!

It should be much easier for someone to post their very schematic than for many others struggling to understand what's really going on..

P.S.
As per your last statement, you've found resistors proper values so vivere in pace e serenità..

[duck_arse]

both the electros are backwards.

[ElectricDruid]

both the electros are backwards.

and if we believe the notations, it's running on 18V. But I don't.

[antonis]

and if we believe the notations, it's running on 18V. But I don't.

So you didn't see her face, yet..

P.S.
Sorry guys but OP clearly stated that he only needed resistors values..
(irrelevant to circuit's configuration, polarity and supply voltage..)

He also stated that he doesn't need any comment about his "mysterious" circuit, so plz, don't be rude against such a polite/noble/gentle/gracious person..

[idsnowdog]

> Q1 and Q2 were too interdependent to allow me to zero in on a specific value.

How? They are not DC-coupled. Combined with your remarks on breadboard, I wonder if it is oscillating.

If it is it isn't audible.  If my termites can hear it they can move out.

[antonis]

> Q1 and Q2 were too interdependent to allow me to zero in on a specific value.
How? They are not DC-coupled. Combined with your remarks on breadboard, I wonder if it is oscillating.

If it is it isn't audible.  If my termites can hear it they can move out.

In case of your termites prefer to shack up with you, place a 47 - 100 pF cap across R3 & R5..