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Old 7th Dec 2009, 2:44 pm   #1
YT2095UK
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Thumbs up My new Superheterodyne!

I`v Finally learned enough to design AND build my own Superhet radio from scratch.
and although it`s only a Simple LW/MW set it works better than some production sets I have
I can pick up the station `Gold` just perfectly without distortion or bleedover from the chan that`s next to it (several other sets I have get this problem).
the Volume is plenty loud enough without distortion, and because I don`t have a dial to calibrate it to, the tracking was really easy!
I`v attactched a few pictures of it below, it`s only a Simple set and just a prototype so please don`t laugh at the wiring and hangy off / sticky outy bits
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Old 7th Dec 2009, 3:01 pm   #2
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Default Re: my New Super Hetrodyne!

Well done. I like the construction method, perfectly sensible. Ideal for listening to any music composed or played by Sir Henry Wood
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Old 7th Dec 2009, 5:32 pm   #3
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Default Re: my New Super Hetrodyne!

Thanks, although I have confess that pulling the 470K I.F to 455 was a bit of struggle doing it by ear when I`d forgotten to connect up the Ground for the tunning coils and could only get a signal with a longwire, seems a longwire can act as a ground to?
half a morning later I discovered the connection that I should have made and didn`t, and it all burst into life perfectly when I completed it.
I was hopping it would pick up off the ferrite rod alone, but only the very strongest stations come through, which turned out to be an advange for tuning and peaking of the audio and signals.
so now it has a Antenna coil on the ferrite rod, and it serves both LW and MW well.
maybe the ECH81 isn`t the best mixer front end to use?
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Old 7th Dec 2009, 9:17 pm   #4
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Default Re: My new Superheterodyne!

Quote:
maybe the ECH81 isn`t the best mixer front end to use?
The ECH81 is generally reckoned to be a very good frequency changer. It is more than adequate for normal broadcast receivers.

If you are suffering from low sensitivity, then you may need to re-check the alignment and tracking of antenna and local oscillator circuits. Good tracking is important, but quite hard to achieve without a lot of calculations.
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Old 7th Dec 2009, 9:29 pm   #5
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Default Re: My new Superheterodyne!

done

I can get More stations now without an antenna and plenty foriegn ones now that it`s evening With an antenna.
even bringing my hand close to the ferrite will bring in stations.
whislt experimenting with different "settings" I noticed that I can get the same chans Twice, either side of the peak of whistle, and also several "channels" up on the main variable cap.
the higher frequency replicants are bit weaker though.

anyway, it`s now Whistle free and chocka block full of stations all over the place.
it Must be good... even my Wife likes it!
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Old 7th Dec 2009, 9:53 pm   #6
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Default Re: My new Superheterodyne!

do you have a schematic i would love to see it
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Old 7th Dec 2009, 10:07 pm   #7
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Default Re: My new Superheterodyne!

no, not yet, I haven`t drawn one.
it`s about half a dozen peices of paper all over my desk with bit`s crossed out and stuff added here and there etc...
nothing cogent to anyone else but Me currently.
but yes, I will get around to drawing one up for you fairly soon as I don`t want to forget either, Some of it Isn`t on paper though, and just made up direcly from my head (the Amp stage is such a section) as I didn`t feel the need to write it down because those are easy to make.

I also would like to see what it Looks like when all put together on one page too
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Old 7th Dec 2009, 10:22 pm   #8
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Default Re: My new Superheterodyne!

Nice work, are you going to go all the way and build a cabinet for it?

If you do go for mass production, you'll have to think of another name; YT2095UK Radio doesn't quite have the same 'ring' to it as Ekco or Bush.........
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Old 7th Dec 2009, 10:40 pm   #9
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Default Re: My new Superheterodyne!

Quote:
Originally Posted by YT2095UK View Post
done


whislt experimenting with different "settings" I noticed that I can get the same chans Twice, either side of the peak of whistle, and also several "channels" up on the main variable cap.
the higher frequency replicants are bit weaker though.
That's 'second channel' interference. You probably need to experiment with the aerial tuning against oscillator tracking...difficult to get it right without the calculations and I don't have the math for it either!

Rich.
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Old 7th Dec 2009, 10:46 pm   #10
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Default Re: My new Superheterodyne!

I hope to make a case for it eventually yes, but I`m lacking some parts at the moment such as a Speaker for it and other little bits that I can design around.
this radio is all made from "Scrap" and "Spares", seems only fitting that rest should be also
so I`m sure that given time I`ll come across a speaker and some bits of wood etc...

LOL, even the Circuit board supports are made out of Rocket Sticks that landed in the garden!

Quote:
Originally Posted by Richard_Newman View Post
That's 'second channel' interference. You probably need to experiment with the aerial tuning against oscillator tracking...difficult to get it right without the calculations and I don't have the math for it either!

Rich.
I`v gotten there eventually with Trial and Error and doing it all "By Ear".
seems to be working quite well now
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Old 8th Dec 2009, 2:46 pm   #11
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Default Re: My new Superheterodyne!

Well done that man! Building a set from scratch is a really worthwhile and satisfying experience. I'm a bit confused why you had to change the IFTs to 455 KHz though. Could you only get an oscillator coil to match that IF?

If the aerial coils and the oscillator coils weren't a matched pair, then you've done very well to get such good results adjusting the tracking by ear. Lots of fiddling about with trimmers, padders and signal generators is usually necessary to get this right.

Looking forward to seeing the full circuit!

Cheers,
Neil
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Old 8th Dec 2009, 3:24 pm   #12
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Default Re: My new Superheterodyne!

Well, the tuning knobs look to be Cossor.... Possibly you could make a name for this beast out of the makes it is made from. Like a labradoodle!

Well done



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Old 8th Dec 2009, 4:57 pm   #13
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Default Re: My new Superheterodyne!

Neil; the Osc coils and Tuning coils are out of a Murphy 198, as is most of the ferrite for the coils (it was a broken one that I cut to size with a Dremel), the Antenna coupling coil is from a Bush, these are 455k.
the Transformers are from a Cossor and work(ed) at roughly 470K, so I had to pull them together manually, padding caps are Beehive types out of an old Oscilloscope as are the new knobs on it (they Were Cossor ones in the picture),
the output transformer and variable cap are ones I bought second hand off ebay, and the valves are out my collection that I`v had over 20 years now and finally decided to learn about this technology Propperly.

there really isn`t Much at all to waste on an a "Scrap" radio, even the chassis is a great building block for any number of things, esp since it has all the valve blanks pre cut out for you

so this This radio has Plenty of names to lend itself towards a final name, although it`ll probably be as long as that railway station in Wales!

I`ll probably get the cct diagram done in the morning as I`v been to the dentist today and had some work done and I think that desrves a few shots of Drambui and chill-out with a good book
the valve line up is: ECH81, EF91, EBC90 and an EL84 though.
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Old 8th Dec 2009, 6:42 pm   #14
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Default Re: My new Superheterodyne!

ok, I`m quite a bit of pain at the moment and May not feel like doing much in the morning beyond feeling sorry for myself, so I`ll post the most cogent parts of my cct diag as I have them (remember I designed it a Modular system and that`s why it`s in Parts), but it`s all you`ll need to make your own as the pictures are in the correct order.
this is ONLY a Protype and not the finished item yet as I still have to play about with different values here and there, and the mixer needs a little bit more work as the very ends of the tunning range result in Odd (non radio like) noises.
currently I`m just treating it as if it`s a new radio I`v just had in that needs a little fixing up, so build one with that in mind and you won`t go wrong
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Old 8th Dec 2009, 9:08 pm   #15
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Default Re: My new Superheterodyne!

It's pretty conventional and good for a starter. One question...why is the cathode bypass capacitor on the EL84 cathode only 82pF? It's not going to do anything at that value. It should be 25uF (22uF in new money) or there abouts. Or leave it out altogether if you have enough audio gain to introduce a small amount of negative feedback. You may find an improvement in volume by taking the screen grid straight to HT (usual) but check the current through the valve afterwards.

Well done for getting this going.


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Old 8th Dec 2009, 9:15 pm   #16
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Default Re: My new Superheterodyne!

I got that used to doing pF after the Mixer stage I did the same for the amp too, it`s actually uF, I just filled in all the values After I drew the diag.
some of the caps are marked as 503 or 101, I think just as well in those terms too.
consider these Pre-Publication diags just to fill a time gap for now.
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Old 9th Dec 2009, 7:55 pm   #17
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Default Re: My new Superheterodyne!

I hope that it an error in the drawing but there is no grid resistor shown on g 1 of the ech81 so bias wil be faulty
regards Trev
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Old 9th Dec 2009, 8:06 pm   #18
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Default Re: My new Superheterodyne!

with or without makes no audible difference at all, it`s not an error however, it was left out for later when I try to work out an AGC for it and then fill in the gaps.
these are my Pre-Build diags, but will still work as they are (I`m listening to it Now and have been most of the day).
drop a 1 meg from pin 2 to deck if you like though
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Old 9th Dec 2009, 8:16 pm   #19
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Default Re: My new Superheterodyne!

And the EL84 volume control is wired funny too! Take the wiper to the EL84 grid (not the coupling cap) and the other terminal to the coupling cap (not the EL84 grid).

It'll work as you have it, but at low volume there'll be bass cut. Also, the relationship of control position to volume will be a bit funny.

Congratulations on getting it working though! There's so much satisfaction in switching on your own work, watching the cathodes heat up, and then hearing the results! Is this the first of many??
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Old 9th Dec 2009, 8:26 pm   #20
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Default Re: My new Superheterodyne!

wow, Thanks!

yes, hoepfully it will be only the 1`st, as I`d like to do a 0-30MHz with dirty great wave change switches and a BFO and it`s got to have one of those Magic Eyes in it as well (I`m determined to find some Usefull application for this one I have here).

for the Wiper arrangement, I did it that way as the 470K constant resistance was a grid bias, but I can see what you mean about the bass, I`ll swap the 2 wires around and put a 1Meg from grid to base Should anything happen to the volume pot in way of momentary contact loss or dust.
good call, Thanks

AND I`ll add an On/Off switch too whilst I`m at it, I seem to overlook the simple stuff
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