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.
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