Back into the workshop and radio receivers!
I was quite impressed with a lash up of an AFC system I played with some years ago.
Of late I wondered if I could make an add on AFC system that could clip onto any Superhet.
I did some lab work on the subject and came to the conclusion that It was impractical.
I did on article on this subject and i'll send a PDF to Brad to pin to this post.

Fred.

Automatic frequency control

What you'd need, Fred, is a ratio detector. A special winding for 455kHz.

Connect the output to a varicap diode, couple this lightly into the oscillator.

Document uploaded.

Hi Ian, yeh thats where you start!

The discriminator was the easy bit.

Tapping into a radio without pulling the chassis out of the cabinet is the practical problem!
My bright idea of connecting an outboard device into a radio by two leads is the impractical bit as explained in the article.
Making the electronics work was just normal problem overcoming.

The method of local oscillator control was not so hard.
I trialed and proved the four text book methods of control worked.
None of that work has been documented as articles.

1/ Miller effect of triode
2/ Varactor diode with control vlave
2/ Reactor valve with inductance phase shift
4/ Reactor valve with capacitive phase shift.
Fascinating to see valves do things that they were not meant to do! but each method really does work.

All four methods worked like a charm BUT you have to build each circuit into the set chassis as part of the tuning system!
All the tuned circuits have to be aligned as one to work in a practical sense.

Oh well another bright idea shot down, but you got to try and explain why some idea does not fly!

Fred.

If you wish to study a Miller "Transitron" Oscillator, my Heathkit OS-1 uses one. This Oscilloscope also sends that signal to the "X' amp socket, which can be extremely useful.

Since that last effort I am now in the process of building and proving a complete auto tune set.
In doing this I am trying many circuits and ideas and just to raise the degree of difficulty am using vlaves of the era.
That is metal octal base, 6SK7, 6SJ7, 6SA7 and so forth.
Why am I doing this?
Because I can!
But i'm rapidly finding out why the idea never became a commercial reality with that technology.

It is proving to be entertaining and once more showing me how little I actually know about coil design and valve circuits!
There are so many variables in making a "simple" superhet receiver just work, let alone work well.
This auto tume concept demands that the entire set work VERY WELL not just pick up stations like your average set.
It a very holistic thing as any change in one section immediately affects every other section.
The one good thing is the thousands of pages in the Radiotron designers handbook and many papers written at the time by authors and the valve companies, are actually starting to make sense.

The research continues on at a slow pace, I can only manage an hour or two every other day in the workshop.
I'll follow up with an article once I get sick of it and want to do something else.
Stand by!

Fred.

In the Valve era it was tied to affordability & competitive edge, which did tend to stifle putting features into domestic radios, which would make them more expensive.

As far as locking things on frequency. The Wadley Loop from South Africa was the most successful. There was some sort of electromechanical method of calibration the wartime frequency meters, like BC 221-N and family and converting it to print.

The fun of the fair is getting the oscillator to jump in steps which would need voltage regulation of heaters & plates and possibly a voltage controlled oscillator, Complicated by the thermal drift of tubes.

Part of the secret with the BC series was the batteries, which tended to maintain a fairly constant voltage.

I have accumulated, from various sources, a handy library of tube, TV, test gear, & radio related books & data.

Fred, you are a living testament to neuroplasticity and life-long learning!

Happy Christmas mate! May you see and enjoy many more!

Thanks Ian and Marcc!

You all know the Dunning Kruger classic curve of knowledge.
Having ascended to the top of the first peak in relation to valves and design (i thought), the last 10years has proven to me I actually know bugger all about the subject and I have plunged into the 'valley of despair'.
I have never read such a load of BS about the subject of Superhets and valve theory that inhabits the internet and scientific teaching now.
AI is only making it worse.
"Authors" write with authority on valve subjects but after top layer analysis, most "experts" are simply copy/pasting each other using AI to wrap a blanket of different "credible" sounding words that mean nothing. They just spew out the same junk over and over.
I find the only creditable sources to do with valves are trade journals, university papers and books written before 1970 or so.

The rest is rubbish.
I have actually found a lot of sense in books written around the end of the 1800's!
Anyway, I'll get there.
Fred.

I would agree that there are a lot who can only be considered a font of ignorance & legends in there lunchtime. This is where a lot of the older books I have are a lot more use.

I think one can make some sort of comparison with the genius who realised you could charge a mobile telephone using radio waves. This concept of transmitting electricity was proven by Tesla in 1912. Looking at some pictures in tombs I suspect it goes back further than him.


Marc

I don't rate AI but am happy to accept it where it does actually provide a benefit. I am thinking that AI is like anything else - with good and bad elements. It is currently being widely abused. I watched a video (not the whole video, mind you) on Youtube last night supposedly showing how Australia's polymer banknotes are made. The video was a pile of BS from start to finish and didn't even rate as what we used to call trick photography. I am not sure whether or not the editor simply was practicing skills he'll obviously never acquire or just being there to deliberately deceive. And here's the clincher - when you watch a video on this subject and out the other end pops a wad of US $100 banknotes which are still to this day made of paper, it is easy for even a dunce to guess that something ain't right.

Youtube is then caught in a mire - such videos don't technically breach any of their publishing terms, so they don't pull them down. To pull them down means less advertising revenue. The downside is that Youtube is becoming more and more a cesspool of lies.

As a farmer AI was always artificial Insemination..............

As with everything there are always those self centred nutters who need to get a life, & those greed driven, willing to exploit and use things for malicious intent, spoiling it for every body else.

YouTube or whoever is carrying it is determined by its inconsumable greed, to destroy itself. Adds every two minutes really get under your skin and drive you to quitting. Its no longer entertainment: Its an ordeal.

I have wrapped up the building part of this AFC project and transcribed a lot of notes into a short 'thesis' on AFC plus some interesting ideas about how a 'superhet radio' actually works.
The more I look at it the 'superhetrodyne' receiver design was just a bodge up work around to use the parts available.
The set was an interesting build.
More work to do is to re-write the 'thesis' in a shorter form for magazine printing.

An Auto Tuning 1940s AM Radio

Document uploaded to Post 13.