03-05-2021, 12:41 PM
Quote:I'm not near any relavent information at the moment, but experiments with twin triodes designed for cascode amplifier use do seem a little reluctant to oscillate, on one occasion particularly in my case because I tried to use the section in a type that has its internal screen connected to its grid! I don't suppose you have done anything that silly One aside that worked surprisingly well, was while investigating superregenerator circuits, that they don't take a lot of modification to produce an acceptable self oscillating mixer for a low IF pulse counting FM receiver ...
The home brew IF transformer experiments I will claim as a resounding success, however trying the same shortcut to make a local oscillator for a superhet has proved difficult as the available range of values don't coincide with anything that will allow decent tracking... We can't have it all though.
Glad your IF experiments are successful. After reading your post, I have checked in case I was a muppet. The internal grid pin 9 for ECC85 is grounded. The Hartley oscillator is very simple and I checked many times for silly mistakes. I never had any issue with oscillators using pentagrid values for MW. With FM, thing starts to get difficult and unforgiving for wirings and components layout. I tested the nuvistor pre-amp and mixer, they are all working. When i probe the anode resistor of the ECC85, it starts to oscillate strongly!!! I cannot find a logical explanation for it. I use a cheap TinySA spectrum analyzer with its antenna to check oscillation frequency and strength. Any scope probing would load down and detune the oscillator at VHF frequency. Once I get the oscillator working, it will be all fine.
I keep thinking about the shorten quater wave transmission line used in the oscillator of the Leak Trough Line:
http://www.adventuresinhifiaudio.com/18/...er-design/
I wonder i can make a FM oscillator rig with a coaxial copper pipe as 1/4 transmission line.
I built a one valve 6C4 (half 12au7) superregenative FM receiver last year, it worked ok. I have not explored low pulse counting FM yet.