Doubt about the Polish PI

[MOR_AL]

Hi!
I finally understood what may be happening with this T3 current source circuit.
The + 5V voltage source is 17V above GND.
The -5V voltage source is 7V above GND. + 5V and -5V around 12V.
So T3 can be correctly polarized.
The only problem is that I don't know if the emitter is intentionally exchanged with the collector and if the intention was to reduce the HFE of the T3 transistor, or if there was a mistake when it came to drawing the schematic diagram. The circuit would function as a more efficient current source, if the collector was exchanged with the emitter.
MOR_AL

[Skippy]

Those crazy Polish, eh ? Indeed, the +12V supply rail is 5 volts less than the +5V supply rail. And the -5V rail isn't -5V. It sure made me look twice before I answered originally.
However, the important point is the 555 oscillator is powered from +12V and 0V ( sort of .... there's some drop on that 180R resistor in the -ve supply to the IC ) .... so that transistor still has to pass current from the +12V rail into the resistor and capacitor ( R22, C12 ) of the 555 circuit. And that is not easily going to happen with a reverse-biased base-emitter junction of a pnp bipolar transistor.
I still feel my original suggestion is valid.

One important bit of info that I'm unsure of ( I'm no PI boffin ) is what is the voltage out of IC3 when a signal is detected ? If it goes positive, and above the +12V rail, then I see your point, the transistor could function as a very low beta h_fe pnp device, with emitter and collector reversed. The transistor doesn't appear to need any gain to function like this, the op-amp can source the necessary current to work the 555 charge/discharge circuitry. So the purpose of the transistor is just as a 'switch' - if the voltage from the opamp exceeds the +12V rail ( by 0.6V ) then it allows conduction, otherwise, it's non-conducting.

( from what I recall, using bjt's reversed was something that people did in the early days, perhaps Germanium-era, as they were not so well optimised for one particular mode of operation then. Any silicon device made after the 1960's is going to be pretty hopeless when used 'reversed' , very low beta, and probably other unwanted features too.
The only circuit I can recall that intentionally used this technique was a small-signal audio amplifier, for, I think, moving-coil record-player pickup cartridge amplification. It had multiple transistors in parallel to reduce noise levels, and was powered from two 1.5V cells, as +1.5V and -1.5V supplies. It was probably in one of those giant 'Markus' compilation books of thousands of wierd circuits. )

[MOR_AL]

...
The transistor doesn't appear to need any gain to function like this, the op-amp can source the necessary current to work the 555 charge/discharge circuitry. So the purpose of the transistor is just as a 'switch' - if the voltage from the opamp exceeds the +12V rail ( by 0.6V ) then it allows conduction, otherwise, it's non-conducting.
...)

The purpose of transistor T3 is to provide a voltage-controlled current source at the output of IC3.
I (emitter) = [ V(out IC3) - Vbe - 12V - R21 * Ib ] / R20
I (emitter) ~ = [ V(out IC3) - Vbe - 12V ] / R20
For V(out IC3) > Vbe + 12V

The T3 function also limits the oscillation from IC6 to V(out IC3) > Vbe + 12V
If V(out IC3) < Vbe + 12V, IR22 = 0 and the oscillation is interrupted.

MOR_AL