[Amps] Tuned Input and the MFJ-259B

[rlm]

On Friday, October 24, 2003, at 08:42  AM, Vic Rosenthal wrote:

> Aargh!  I SHOULD have said:
>
> You probably know this, but the correct way to do it is to temporarily
> put a non-inductive resistor equal to the input impedance of your tubes
> under operating conditions FROM CATHODE TO GROUND, and do the test 
> with the amplifier powered off.
>
****  There is no such thing as a non-inductive resistor.  There is no 
such thing as a g-g amplifier that has a fixed, cast in bronze  
___+/-J0 ohms input Z  For example, a 3-500Z-cathode looks like c. 
35-ohms at the negative peak of input V, and is has virtually 
∞(infinite)ohms at the positive peak of input V ( when cathode I=0).  
The best load for adjusting a g-g tuned input is the cathode.  However, 
at least 50% of the normal drive power is needed -- or, one can use 
high-speed dits at 100%.
--  Another 'gotcha' in adjusting a tuned input with a terminating R  
is that any Q will do.  In the today's world of solid-state radios, 
this is undoubtedly Not the case.

  ---  Murphy was right about things not being as simple as they first 
look.