Robert Casey wrote:

John Byrns wrote:

In article , Patrick Turner
wrote:



John Byrns wrote:



In article , Patrick Turner
wrote:



Better of course would be to have a CF tube to accept the IF envelope,
and the low impedance output from the CF can then power a crystal


diode, or


a tube diode
in a variety of ways I have previously explained in post on the matter.


You still haven't explained how this added cathode follower, to drive the
detector, helps matters? Many experts even make the claim that a finite
source resistance can be beneficial in reducing distortion, especially
high frequency distortion.


IN my case there *is* a finite source resistance which is the 100k
R across each IFT winding.



Yes, but the diode is driven from the low source impedance of the cathode
follower, not something on the order of 100k. Why not eliminate the
cathode follower and choose the diode detector load so that it looks like
100k to the IFT at 455 kHz?



The detector diode is a nonlinear load, where a resistor is. Not sure,
but the non linearity
might cause distortions in the IF transformer. In that the loading of
the IF transformer's Q
is varying, thus the bandwidth is varying.

The diode loading of the IFT does cause some non linearity in the IF amp,
which is detected, and comes out as audio thd/imd.
In my radio there is no AVC applied to the IF amp which is a sharp cut off type
6BX6,
with an unbypassed Rk, and with the lower than usual IFT but linear R load
only, there is a fair current change in the IF tube, so a fair amount of current
fb from Rk,
so the IF tube amplifies the enevelope with far better linearity than most other

sets I have examined.

Patrick Turner.