On Thu, Mar 29, 2018 at 01:26 pm, Fabio Trevisan wrote:
8. Last, but not least, while checking the waveforms at the bases and emitters
of Q2441 and Q2541, the looked rather different (the peak-peak amplitude at
one of them was much bigger than the other (about double)...
However, there's no distinguishable difference of the waveforms at their
collectors (maybe because they are balancing out?)
Taking both transistors out, and testing them on my AVR transistor tester, one
showed distinctively different than the other, more than I would consider
normal for 2 transistors being used on a complementary stage like this.
A difference of almost 20mV in Vbe (one have 700mV the other 720mV), and a
difference of about 30% of hFE (one have 35, the other almost 50).
Questions:
B. Can those transistors be causing the problem? What would be a modern,
currently available equivalent to an A5T4261 transistor?
It's a 2GHz fT; 2.5pF Ccb; >30hFE; 12V VCEmax, 80mA Icmax
Fabio, 151-0271-00 is not a matched pair, so Tek didn't judge that necessary . 20 mV difference is not important at all since these transistors are current driven at the emitter. The transistors in the previous pair Q2405/2505 have (or should have) enough headroom in Vce (maybe check this). This also explains that you see no difference in collector signal. Difference in hfe could do more harm perhaps, though I also doubt this.
A suitable replacement would be 2N4261. Sphere has a few new in stock under 151-0434-00, $6 each. In the cross ref also listed as 151-0271-00.
Albert
