Quote:
Originally Posted by Sideband
Unless I'm missing something, are they using the screen grid of the reflex stage as a 'virtual anode' and taking the audio from there  ? |
Yes, lovely isn't it. I've always been very fond of this electron coupled notion, also used in the electron coupled oscillator and TV sync sep circuits, and others, it makes great use of the utility value of the screen grid. Getting more functionality out of the one part.
I have attached another circuit of a reflexed set with a more conventional volume control and another image helping to explain the stage, in this case audio extracted from anode in the other image.
I would make a general remark though about the whole idea of of building a minimal superhet...it could go to far. Others may disagree:
Obviously, after a lot of research here in AU, these reflexed superhets were commercialized and worked pretty well. They are really about as minimal as you can go simplifying a
superhet without flushing the radio's performance down the toilet.
I don't think cutting back to less than three active stages: (converter/IF(reflexed)/Audio) for a superhet is a good idea at all and that is getting double use of one stage.
Of course you can use valves with triodes & pentodes etc in the one envelope to "cut back the valve count" and convince yourself it is simplified but it doesn't really change the fundamental gain-bandwidth requirement. Unless you want to make a "deaf superhet". Likewise adding in regeneration to acquire more gain, is a difficult thing to control.
In my view there is not a lot of point of putting in the construction work to make a badly performing radio. If you make one at all, it is nice that it would be a peppy performer, at least that is what I think.
On the other hand with other radio designs with regenerative detectors etc, very simple low valve count radios can be made, but they are not superhets and they have their quirks.