Albert,
Thanks for the heads up... my remarks just after your quote.
On Fri, Mar 30, 2018 at 01:12 pm, Albert Otten wrote:
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.
As you will see on my other reply to Roger, I managed to make the proper vertical LF step response right, by using the LF adjustments there are on the vertical plugin.
Those transistors though, seem to have become less important (but opportunely, I will try to find a replacement).
I also found, on the Tek semiconductor x-ref, that there seem to be a difference between the part 151-0271-00 and the 151-0434-00.
While the latter is indeed a direct equivalent to the 2N4261, it seems the 151-0271-00 is a variation of the 4261, which they called the A5T-4261.
The a5T kind is an 80mA Ic part, while the vanilla 2n4261 is a 30mA part.
The A5T has a TO-92 package and seems also to be capable of dissipating more power as well (0.5W against 0.2W the TO-72A package of the 2n4261).
Krgrds,
Fabio
Fabio Trevisan