1980 Soviet Radio Cassette amplifier problem.

[Richard9025]

More updates:
I searched and I searched through every PNP transistor which I could get my hands on...
The only transistor, which I initially thought it was a low-gain PNP transistor, was a military-grade TO39 or TO5? transistor which was marked as "2N2905" on the schematic. It doesn't have any writing on it, just a radiator attached to it:


With this in the circuit, EXACTLY THE SAME effects as with the original T3...
BUT I found why:
I said let's test the gain of these transistors!

This transistor (Actually I think it is a 2n2905a) - 142
The original T3 - 248 !!!
BC556B - 376

T3 clearly is defective, 248 is a lot over the maximum 160 in the datasheet...
The shops are closed Monday and Thursday, so I'll continue looking for a low gain PNP transistor.

OFF TOPIC--- For Dr. Edd:
I found this ruler while searching, why is it written "ALLIED EQUIPMENT" on it? Is it a ww2 relic?
It measures Inches and Centimeters, the writing changes as the angle of the incoming light changes

 

[Richard9025]

I went to the local electronics shop and I got some BF506 transistors.
Out of them all, the lowest gain that I could measure was 57.
Then I put the BF506 in place of T3
Results: NOTHING CHANGES...
I've also replaced the remaining T1 and T9 with some 2N3904s
Results, again nothing changes...

So all the transistors in the radio unit (A4) are replaced, still, nothing changes.
I did as much as I could to check almost all the components in the radio block, this radio is driving me crazy!

Until I get a reply, I'll check the electrolytic replacement capacitors, maybe they are bad from the factory?
I really need to fix this unit kinda fast, I got a nice Philips combo from the 80s that has some little issues regarding the stylus and cassette belts, and a 70's radio that's popping fuses. This unit is occupying all of my workbench! And I need to clean it because it's a mess!

Maybe T3 should have an even lower gain? (the original T3, kt326b should've had a gain of minimum 25)

Recording with the audio that is currently produced by the radio(with all the changed transistors):
https://vocaroo.com/i/s0ZsDpMv4Oyh

Thanks!

 

[Richard9025]

I got the following advice: Power the radio and the amplifier units separately.

I managed to separate the two units, so only the screened wire that carries the detected and preamplified signal is left connected to both units.



Okay, so with the 2 units completely isolated by means of supplies, I get the following RESULTS:

The powering method doesn't matter, reversing the supplies (power supply for the amp and batteries for the radio block) produce the exact same effects. powering the two units from separate batteries produce the exact same effect also.)

I get very clear audio, with some buzzing in the background (it is from the screening, not from the power supply!!!)
BUT at max volume, it is quiet, a third of what a radio from the same period is producing in means of loudness.
https://vocaroo.com/i/s0uSjkl6aHiy
recording with max volume, notice how the buzzing is altering between loud and quiet. It's because I didn't hold the microphone still, in reality, the buzzing is constant.

This test deduces poor grounding? or filtering? or interrupted ground?

I also got this advice regarding how the radio works:

"when running on FM, the intermediate frequency signal FM goes through the AM circuit, which has the oscillator off and acts as an IF-FM amplifier"

Thanks!