Well some of the 7 GHz and higher Ft transistors have internal matching networks to prevent such oscillations, but yes it is an important issue.
73 de N1UL Sent from my iPhone > On Oct 14, 2018, at 4:14 PM, Richard (Rick) Karlquist <rich...@karlquist.com> > wrote: > > > >> On 10/14/2018 11:20 AM, Dr. Ulrich L. Rohde via time-nuts wrote: >> Actually the BFT is out of production since quite a while there are more >> stable and higher Ft devices on the market. >> 73 de N1UL > > How is a higher Ft device more stable? Those attributes > would seem to be mutually exclusive. > > For time nuts purposes, I would submit this is a bad trend. > What we want is higher DC beta, not higher Ft. The higher > Ft just makes the device want to oscillate. For any designs > I do, I put a 100 ohm resistor in series with the collector > as an oscillation killer. > > There is a similar problem with gain block amplifiers having > bandwidths into the double digit GHz. I routinely put a > 10 pF capacitor directly from input to ground to kill high > frequencies. > > A related problem is that newer devices have lower base > spreading resistance. This does help with noise figure > but again risks HF oscillations. > > Rick N6RK _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.