You Vintage radio folk will be pleased to see one of my more "out there" builds has made it into print in Silicon Chip.
I got my July issue in the mail and on page 80 we have the 6Y9 single valve Superhet as the "vintage radio" article.
I rewrote it to magazine length and Bao Smith did a good job into translating that into "SC speak".
The article runs over 6 pages.
My thanks to Ian Robertson for the original idea and help while developing the thing.

I have submitted quite a few items from this Special Projects section, but of course in much shorter form suitable for magazine editing.
It also helps that I have written hundreds of articles and self-published my own book, no, not on radios but Australian coins.
That experience has helped me understand what magazine editors want in submissions.

Cars, coins, vintage radios may sound different things to write about, but not really.
I found editors like a story well told and can pick if the writer knows what they are talking about.

One of the builds I have submitted is the original "Little General".
Will it see print?
Who knows?
In the meantime, enjoy seeing a "VR" project in Silicon Chip!
Fred.

Good stuff, Fred. My trick will be that I haven't subscribed for a few years now. I will have to do things the old fashioned way and grab a copy from the newsagent.

Hi Brad.
Interesting thing about SC was I stopped getting it from 2005 to about 2015 because every tech article (so it seemed) was a variation of using a PIC chip to do what could be done with 2 transistors or a couple of relays.
The science articles were non existent or superficial.
However with the current management and editor the constructional articles cover a lot of topics using a wide range of techniques (including transistors and relays!) and a lot of modern science is covered by contributors that know what they are talking about.
I re-commenced subscribing and have learnt a lot.
Fred.

Yes, it was getting a bit like that and even so, I've never once used a PIC AXE or whatever they are called now. I like meat and potatoes electronics but probably because that is what I dealt with when I was a young lad.

Hi Fred,

I saw your article about this one-valve superhet set in Silicon Chip in July, and am interested in building it. I have just two questions, as follows:-

(1) You have rewound the secondaries of a Jaycar power transformer to give 6.3V AC and 140V AC (under load) windings. For both, how many turns and what B&S gauges of winding wire are required?

(2) I think I can get a 6Y9 from a fellow member of the HRSA or from their valve bank , but am wondering about a 10-pin socket. Can you supply one? Failing that, I might have to get some help from Mr ebay.

Hoping for a reply soon. Thanks,

Rod Peeler

Hi Rod, Ian here.

If you look back in the circuits posted here you'll find some of my circuits as the concept was developed. There is a power supply design that uses readily available, off-the shelf transformers. Fred is fortunate in that he can wind transformers, a skill I'm in awe of! For us mere mortals, an off-the-shelf solution might be more attractive.

I just checked and the version of the circuit to which I referred is not there. My email is open, email me & I'll go looking for it on the upstairs PC!

10 pin "decal" sockets are readily available on Alibaba.

A 6Y9 is also known as EFL200. You can also use a PFL200 that has a different heater voltage but is otherwise the same.

Adding to Ians above #66,

Hi Rod, the valves and sockets all came from suppliers on eBay.
They were quite cheap so get a couple of sockets and valves.

I'll dig out the specs tomorrow on the PT wind, may also be in this thread series, can't remember..

Yes, please do have a shot at making one from the circuit it will be fascinating to see what trouble you get into!!
Probably be best to follow the same physical layout to get the same web of signal fields fromk the various wires.

Any questions just fire away on this thread.
We will be tickled pink to see another version made.

Fred.

Rod, I had to read over the project and figure out what I did about the power tranny!
Lucky I took some photos as you see in the posts.
sometimes I work so fast I just make something and then forget.

Looks like I took a MM2011 pulled it apart and just re-wound the secondary bobbin.
The primary bobbin stays as is.
My notes folder has a scribbled 6.37 turns per volt (we are looking at scraps of paper here).
That means I connected 240 to the transformer and measured what the secondary voltage was.
Then I stripped the tranny and unwound the secondary counting the turns.
Then I could work out the turns per volt
.
My scribble then says 6v heater 44 turns of 0.18" wire.
Then 900 turn of 0.0056" wire for 140 volt.
That just fitted in the bobbin.

You coud easily just use a small Jaycar 240:6 volt tranny for the heater and some other little tranny with a diode multiplier off a low voltage secondary to get up to 180 volt DC.
The type of transformer or supply is not important, just getting 6 volt for the heater and about 180 volt dc for the plate supply is the target.

Altronics M6672L, using the 24V and 30V tap for the heater and a voltage tripler will get you there.

The Decal valves benefit from being under-run, they used to have fairly short lives in TVs!

Fred, I wonder if we could sneak a FET in there as the local oscillator? Hide it in the oscillator coil can?? It would get around the cranky autodyne circuit. Or would that be cheating?

Hi Ian, I dont mind a 2 wire device like the diodes but a 3 wire active device has to be against the rules.
Sure would get over the cranky problem though!

I think anybody that has a go at this project will have their hands full getting the 6Y9 working without re-designing the front end.
I think the first way point for Rod will be to get a 6Y9 and wire up a power supply and audio end and get that to work ok.
Then progress to the IF and front end.
I am pretty sure that valve era matching coils are the way to go.
They will handle the voltages and currents ok.
I would not even think of using "transistor" coils like a "superhet" kit of coils from Jaycar.
The power supply can be anything, the speaker and OPT Jaycar, but the IFT's and coils definitely valve era sized.

The point of this set is this: It is inherently unstable when the sections are biassed and tuned for gain.
The feedback ( or magic if you like) then forces stability.
That concept goes against the grain of radio designers.

I would encourage anybody to have a go at this project I learnt a hell of a lot from it and applied lessons to other builds, like my all-metal valve Autodyne.

Fred.

Trying to fit all the gain for a superhet inside one bottle is a bit like Boeing's latest 737s.

Stick 2 thumping big high-bypass turbofans far out in front of the wings (because you're too cheap to re-design the landing gear to allow them to fit in the normal place), making the plane so inherently unstable that no human can fly it.
Solution? Get a computer to do it!

If it's Boeing, I ain't going!

Boeing have made some disastrous decisions in the last ten years or so. The 737 is one of the most popular planes ever made and Boeing turned it from being their mainstay to a computerised anvil just waiting to freefall if the avionics ever develop a non-Windows version of a blue screen and they threw the ball straight to Airbus, which is now selling the A320 in similar numbers.

In the latest SC a nice comment for Ian Batty on the set and some more info about 'neutralisation', (page 6 mail box Sep 24).
I really struggled with the concepts of feedback and neutralising and understanding exactly what is going on.
What I do understand is that it really works!

The issue also has some more Bass Guitar stuff plus a bunch of interesting articles.
Stuff that would never have got near the magazine with the previous editor!

Fred.

Hi Fred, Rod.

Just thinking about why the Autodyne worked reasonably well in early 30's radios and was almost universal with transistors.

Firstly. the radios that used the 58 as an autodyne generally had a carefully-chosen low IF frequency. That would put the resonance of the 1st IF primary well away from the local oscillator frequency so the oscillator wouldn't get "sucked out".

So, would a 198kHz IF do the trick?

Transistors usually used a tapped-down input to the IF, either as single or double tuned. That would make the collector impedance lower and also avoid the suck-out effect.

So, how about a tapped winding?

Maybe even a resistor across the primary to lower the Q?

A set of suitable IFs,. padder and coils could be found in almost any Healing battery valve radio

Ian, the IF frequency is a thing that just eluded me through the process.
You are correct, When I think of the old chassis they were invariably 175Kc IF's.
That would certainly make the 'pulling' effect less serious.
I had a look at my work on Autodyne research where the only type of valve to work well was a hi gain sharp cutoff.
That was, in the case of the metal valve set a 6AC7, the 6SS7 and 6SH7 were not as good.
If I had shifted to a low IF frequency I may have been more successful.
Good point.
Fred.