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Good morning, I wanted to tell you about a problem I'm having with the BFU590s (assuming they are) with which I made a replica of the ALA1530. The one I've used so far has always worked well but it uses PN2222. I then made a second version but with BFUs instead of PNs. The BFUs are marked "S59 W42" and I got them on the Italian TME ecommerce platform (www.tme.eu) and not on Aliexpress or some China page on Ebay. In practice it is impossible to calibrate the 100 ohm trimmer to 0 volts, the absorption always tends to rise, sometimes 140 mA, then it goes to 170 or worse, sometimes then it drops to 160-150 then rise again... and in any case the amplifier doesn't work. There is no point in trying to calibrate it even finely, sometimes I see the voltmeter pointer vary on its own (self-oscillations?). The rest of the circuit is built exactly like the version with PNs, same values ??and everything has already been verified several times. If you have any suggestions for me, I would be grateful. Greetings, F.

Thanks for the reply, everything seems to be working fine now. As you have suggested I put two 33 Ohm resistors in series with the collectors of the two BFUs and now amplifier is regularly working. Now I have that absorption has normalized (now around 100-110 mA stable) and I am able to keep the voltage at the ends of 2.2 uF capacitor C3 with a little adjustment of 100 ohm trimmer, practically stable at 0V (so I also respond to Steve Ratzlaff who wrote to me privately) as well as from the description taken from the Wellgood loop pages here: https://www.george-smart.co.uk/projects/wellgood-loop/wellgood-loop-history/ Ok thank you very much.