[time-nuts] Re: Isolation amp transistors

[Thomas S. Knutsen]

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 <
time-nuts at lists.febo.com>:

> 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<
> time-nuts at lists.febo.com>  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 -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com



-- 
With Best regards, Thomas S. Knutsen.

 Please  avoid sending  me  Word  or  PowerPoint  attachments.