[time-nuts] Re: Isolation amp transistors

[Bob kb8tq]

Hi

The tube cascode has it’s own issues. Setting up a tube circuit for
the sort of isolation we are talking about here is very difficult. 

Bob

> On Jul 6, 2022, at 9:46 PM, glenlist via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> 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
>> 
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