I assume with grounded grid, that you mean a vacuum tube with heated cathode. The cathode will have a noise P = kTB, where T is the red hot cathode, and B is your bandwidth. k is as usual Boltzmann constant.
That said, if you could cancel the capacitances inside the tube, then you could get a decent isolation, but it's much easier with semiconductors. BR. Thomas. tor. 7. jul. 2022 kl. 07:57 skrev glenlist via time-nuts < [email protected]>: > how about grounded grid ? > > Bob can you get better isolation with a vaccuum tube cascode than a > solid state cascode ? > > -glen > > On 07/07/2022 15:22, Bob kb8tq via time-nuts wrote: > > Hi > > > >> On Jul 6, 2022, at 1:53 PM, Richard Karlquist via time-nuts< > [email protected]> wrote: > >> > >> The 2N5179 has high base spreading resistance (decreases isolation). > > As does sticking a resistor (even a small one) in series with the base > …. Yes, inductance > > is even worse. > > > > For “best isolation” in a cascode you very much want the base of the > common base > > stage nailed to ground. Typically “lower” Ft transistors with a decent > base structure > > are the best choice for the common base stage. Both stages benefit from > low 1/F noise > > in the audio range if this is for a phase noise test se > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe send an email to [email protected] -- With Best regards, Thomas S. Knutsen. Please avoid sending me Word or PowerPoint attachments. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe send an email to [email protected]
