Next the sound IF stage, plus!

[AdrianPH]

Another afternoon/evening playing, now have two stages of amp and the diode detector.  I tried 2 x EF91 and in the end changed the second valve to a EF92, this dropped the gain a bit as I run the grids negative wrt cathodes and with the variable mu EF92 it meant a bit less gain.
The rather scruffy underside : -
   
And the better looking topside : -
   
Then out with the radio test set and a few measurements, driving with a -50 dBm output although the display shows as -55 dBm with just a piece of co-ax inserted :-
   
Then with the DUT in place.  On the last coil going to the diode detector, as well as it being a bifilar winding, I also included a 1 turn coil, the idea to allow co-ax to be connected for this test, I guess it would still load the coil, but not as bad as going across the output to the detector.: -
   
This seems to indicate approx 44 dB gain.
   
I changed the Y axis to be 2 dBm per vertical division to give a better indication of bandwidth.
The last picture shows demod, with a -50dBm signal going in 50% A.M. mod, 0.7% distortion: -
   
I am wondering if I will actually have too much gain, time will tell.  I still need to better the PSU before this can be fitted to the TV unit.

Adrian