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Old 17th Jul 2011, 1:10 pm   #1
Mark GØOIW
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Unhappy "Illustrated Teach Yourself Radio" by David Gibson

Did you own a copy of this book? Did you try to build the Two-transistor Receiver in chapter five? Did you get it to work?

As a youngster, I spent weeks trying to get this set to work. Despite having all the correct parts, checking and re-checking everything, and completely rebuilding it several times, I never got a peep out of it.

Of course, I blamed myself. After all, it was from a book, there were even photos of the constructed radio, so it must have been my fault. The grown-ups decided that it was too advanced for me. As I grew more experienced, I decided that I had probably overheated the transistors.

Some thirty years later, I had another look at the book. HANG ON! D2 is forward biased - the collector of the RF transistor is being pulled down to 0.3 volts. It can't possibly work without an isolating capacitor, as similar circuits have.

Look at the circuit and see what you think. There was both a board layout and photos of the set, and the book ran to several editions, but it can't possibly have worked whan constructed according to the instructions. How was such a major error allowed to occur, and be repeated without amendment?
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Old 17th Jul 2011, 1:25 pm   #2
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

maybe polarity of D1 and D2 are reversed.

If reversed, then D1 is forward biased, but collector is then Vbe + Vbatt/2 + Vak = 0.3 + 4.5 + 0.3 = 5.1V


Though that doesn't make a huge amount of sense either. I think a capacitor missing as you say.

What does the photo look like? Diode polarity? Extra capacitor or C1 & R1 in a different location?
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Old 17th Jul 2011, 1:35 pm   #3
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

Some time ago, I sent Paul (Stenning) a copy of this book (or one very similar) to scan for inclusion on his main website but I don't think he ever got round to doing it. If he still has it maybe he can see if this circuit is in there to compare it with.



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Old 17th Jul 2011, 1:56 pm   #4
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

I never tried to build the set as I never had the Denco coils. It was one of just a few radio books in the local library. I have a copy of the 1970 reprint and the circuit is the same. If you follow the layout it is the same as the circuit. I never much liked the way he does the volume controls either which involves progresively shorting the detector diode. This applies to the two transistor audio amp circuit and the Superhet circuit
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Last edited by Cobaltblue; 17th Jul 2011 at 2:13 pm. Reason: Added reference to other circuits in book
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Old 17th Jul 2011, 2:27 pm   #5
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

I put 2 pictures of the circuit layout and two of the "actual radio" as well as a 3rd picture of the superhet showing volume control arrangement. Sorry not scanned PC failure means I am using laptop that doesnt have scanner installed.
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Old 17th Jul 2011, 6:25 pm   #6
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

The polarity of the diodes is consistent between the circuit diagram and the board layout, i.e WRONG. You can't really see the diodes in the photos. I don't know if it might have worked if the diodes were simply reversed, though it certainly looks as if there should be an isolating capacitor.

My friend built the superhet from the book, and that didn't work, either. All the circuits seem unnecessarily complicated - the superhet uses a three-gang capacitor where two would be normal. In the reflex circuit, he uses a two gang capacitor and a second Denco coil where most circuits use a single untuned choke in the collector of the first tranny.
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Old 17th Jul 2011, 7:18 pm   #7
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

I borrowed this book from the local library when I was a kid, I nver built any of the radios as I could not afford the Denco coils. Three years ago whilst looking through a second hand book shop in Australia I found a copy of this book and purchased it for AU$6 about £3. Mine is the 1970 reprint and also has the diode the wrong way round, a possible solution would be to include a capacitor between the collector of TR1 and the diodes.



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Old 18th Jul 2011, 7:55 pm   #8
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

If you disconnect the centre junction of the two diodes from the collector of the OC44 and feed it from the collector via a capacitor, you get a classic voltage doubler detector circuit often used in reflex receivers of this sort. I reckon another capacitor to ground from pin 6 of the yellow coil wouldn't come amiss either.
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Old 19th Jul 2011, 12:13 pm   #9
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

Quote:
Originally Posted by Mark GØOIW View Post
Did you own a copy of this book?
Thanks, Mark!

You have just solved a long-standing mystery of mine! I borrowed that book from the library as a child, at the time when I started to take an interest in electronics and radio. All I could remember was the colour of the cover (yellow) and the style of knob on the front panel! Not much to go on, and I have been looking out in second hand shops and on-line with that much information since then.

I'm off to get a copy...
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Old 20th Jul 2011, 11:22 am   #10
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

Thanks for this thread - it's solved a 40 year mystery.

I have a copy that I purchased recently second hand. I might even still have the coils so perhaps I'll have a go at building it in the light of this new knowldege.

Last edited by Junk Box Nick; 20th Jul 2011 at 11:26 am. Reason: Extra info
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Old 26th Aug 2013, 12:27 pm   #11
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

Hi,

Just found this post whilst looking for info on Denco coils.

Yes, I couldn’t get mine to work either. Like the other contributors in this post I looked at the circuit with experienced eyes a few years ago and also thought the diode configuration was wrong. So like in the other post’s it’s a 42 year old mystery solved and shared.

Remember abandoning the two transistor radio from the Gibson book and using the Denco blue coil in the two transistor radio in the fifth edition of the Gilbert Davey Fun with Radio book, which worked ok.

I did build the crystal set from the Gibson book and that worked, but there’s not much to get wrong there! I remember building the transistor amplifier, which from memory did kind ‘a work, but the AC126 ran very hot! I do remember getting through a couple of AC126 transistors though. I always put this down to using Bi-Pre-Pak ‘own branded’ transistors as I couldn’t easily locate Mullard parts locally.

Looking at the circuit of the amplifier it could benefit from a low value resistor in the emitter of the AC126 and a potential divider bias network.

I have to agree with one of the comments above, The author over engineered some aspects of the projects but I have to add he under engineered some others.

One thing I do remember is the Bi-Pre-Pak AC126 came in a TO5 package whereas the ‘pukka’ Mullard came in the TO1 package.

Terry.
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Old 26th Aug 2013, 2:10 pm   #12
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

We couldn't even get the crystal set to work! I'm pretty sure it was the poor quality headphones we used, but it was a bitter disappointment. I do love this book, though, it was my introduction to electronics.
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Old 26th Aug 2013, 3:54 pm   #13
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

I remember reading this book, either from the library at Caversham or from Highdown School where I was then studying - but this was in the mid 1980s and I though it was too complex and the components hard to find, and I was more interested in music and high quality audio so most of my listening interests were on Band II (FM) anyway...
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Old 26th Aug 2013, 8:05 pm   #14
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

Hi Sue, yes, low impedance phones destroyed many an aspiring engineer's hopes of their crystal set working.
Problem was that most of the cheap ones on sale in those days were low Z

Ed
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Old 26th Aug 2013, 11:16 pm   #15
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

I read this book in the late seventies and have recently obtained another copy with the intention of building the superhet. I actually still have the original IF transformers to re-use and have managed to get some denco coils. I never got the original build to work so hopefully with an extra thirty five years of experience under my belt I will have more success this time. The project has been helped along by Ed with the supply of some transistors and a three gang variable capacitor for the front end. It's a bit of an unusual circuit in the fact that it uses only two IF's and has no AGC. Maybe there's a bit of room for experimentation there. Pure nostalgia.
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Old 27th Aug 2013, 2:50 am   #16
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

My father bought me this book for my 10th birthday, along with an Antex model C soldering iron, in a little blue presentation box with a coil of solder and three bits.

Tried the crystal set, proper headphones etc - didn't work. This would have been in 1972 and was my introduction to electronics and radio.
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Old 27th Aug 2013, 8:55 am   #17
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

I'd suggest filing the book under 'Humour' and building a design that's known to work.

Whatever headphones it was intended to go with, they must have been remarkable. That 50uF AF coupling capacitor into the OC71 should let it work down to one hertz... and the 250uF emitter decoupler isn't far behind. It's not just diodes in unexpected directions.

Don't wear the phones when you switch the beastie on.

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Old 27th Aug 2013, 10:20 am   #18
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

Quote:
Originally Posted by Ed Dinning
Hi Sue, yes, low impedance phones destroyed many an aspiring engineer's hopes of their crystal set working.
Problem was that most of the cheap ones on sale in those days were low Z
My own experience in recent years has been that crystal sets work perfectly well with low Z headphones. By low Z I mean a couple of hundred ohms. Apparently they don't do much for the 'Q' of the circuit though.
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Old 27th Aug 2013, 9:15 pm   #19
Ed_Dinning
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

Hi Graham, that is the crux of the problem, coil loading and low Q. There are plenty of websites with complex crystal set circuits, one even drives an LS by using a TL431 regulator biased in the linear range (but needs a small battery!)

Ed
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Old 2nd Sep 2013, 7:07 am   #20
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Default Re: "Illustrated Teach Yourself Radio" by David Gibson

Quote:
Originally Posted by Mark GØOIW View Post
My friend built the superhet from the book, and that didn't work, either. All the circuits seem unnecessarily complicated - the superhet uses a three-gang capacitor where two would be normal. In the reflex circuit, he uses a two gang capacitor and a second Denco coil where most circuits use a single untuned choke in the collector of the first tranny.
When I was a pup I did build the superhet from this book and it did work. Denco coils were readily available at the time. Talking about dodgy designs, I tried to build several projects from Practcal Wireless by F.G Rayer, and I came to the conclusion that absolutely nothing designed by this writer ever worked! I dont know if anyone else had hours of frustration as a result of dodgy projects
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