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Back to basics...just for fun!

Domestic Valve & Transistor receivers, Radiograms, Gramophones, Amplifiers, Hi-fi, Speakers, Record players, Music centres, Tape machines, Cassette players & Jukeboxes
 
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Back to basics...just for fun!

Post by sideband » Mon Aug 29, 2016 12:03 am

Today with nothing better to do I was going through some boxes of stuff I'd had for years with a view to clearing out anything that was of no further use. I found stuff that I'd had for over 30 years and never touched since...mainly bits of old construction projects...nothing of any real worth. Then to my surprise, I found the remains of the very first successful radio I'd ever built. I actually think it was a re-build since the original had been built on a piece of hardboard. I think this was the second version, identical to the first but built in a neater form with guidance and help from my brother.

The remains still had nearly all the parts including the two transistors, an OC45 and OC71. It was missing the tuning gang, coil, trimmer and choke. I had a sudden desire to see if I could make this circuit work again after all these years. Gang, trimmer and choke, no problem but I would have to wind another coil. I couldn't remember the exact details but something suggested 40 turns tapped at 10 and 10 turns for reaction. I found the original article in Practical Wireless thanks to the wonderful American site that is building up a huge library of all the popular mags. September 1965 ( I remembered 1965 but couldn't remember the month so had to search).

Anyway the upshot of all this is that an hour later, unbelievably, this little set was working again with very little effort. Now what to do? My thoughts are to build it into a small cabinet as a reminder of my first faltering steps into the world of radio. Maybe I should improve it by adding an output stage so that it drives a small speaker...

I remember spending many happy hours listening to this set...Radio Caroline came in exceptionally well.... I've had to use a different earpiece (it was designed for a small crystal type) since my one and only crystal earpiece has deteriorated so I've used a 1000 ohm 'stethoscope' type which I've had for years.

In true 'lash-up' form, I've replaced the missing parts in the original circuit. Amazingly the two electrolytics checked out fine.

Anyone else still have any of their early efforts?
Attachments
js640_SAM_0952.jpg
As found
js640_SAM_0953.jpg
Some of the missing parts, ferrite rod, 2.5mH choke and a 50pF trimmer
js640_SAM_0954.jpg
I'll have to wind a new coil....
js640_SAM_0955.jpg
...like so.....
js640_SAM_0956.jpg
The rebuilt radio....working after 50 years....

 
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Re: Back to basics...just for fun!

Post by Refugee » Mon Aug 29, 2016 11:06 am

Does test equipment qualify?
My transistor tester built when I was a teenager still worked in 2012 when it had its last outing to test some power transistors. It was built to take a series of readings to be plotted on graph paper for those unmarked transistors that were sold in vast quantities in the 1970s to create home brew data sheets.
Unlike the little radio it never got robbed of any parts. Not even its classic 10 pin metal canned 741.
It tests all transistors with a fixed VBE and five collector currents ranging from 1ma to 100ma with a facility to use an external power supply to go up to a couple of amps.
The range selector resistors are drifting out of spec but they can be replaced.
There is no need to replace the 741 op amp that flashed the LEDs to tell me the collector current reading is ready to be taken. It still flashes the LEDs just like it did 40 years ago.
Attachments
DSCF6253.JPG

 
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Re: Back to basics...just for fun!

Post by CTV » Mon Aug 29, 2016 1:23 pm

sideband wrote:Anyone else still have any of their early efforts?........................................In true 'lash-up' form

Not a radio but radio related and if you want 'lash-up', this one is true "A" grade 'lash'

I kept my first ever attempt at home construction about 5 years ago, I called it the "Franken-mitter" the reason will become clear once you've seen the photo, beware its not for the faint hearted . Despite its hideous appearance It worked and still does, Its a low powered A.M. transmitter based on a TL702 with a BC548 as an amp. I dread to think of all the harmonics its kicking out, though I've never scoped it as at the astime I didn't know how to use one. As you can see from the photo, quite an abomination but I couldn't quite bring myself to destroy the poor creature so it sits dribbling in the corner of the workshop. My next project four years later and one I was quite pleased with was the crusty function gen, a much better outcome.

frank.jpg
Don't all puke at once ;)

 
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Re: Back to basics...just for fun!

Post by PYE625 » Mon Aug 29, 2016 1:32 pm

That's a rare device Chris......plenty of air around the components :)
I like the use of the little net-curtain hooks lol

 
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Re: Back to basics...just for fun!

Post by sideband » Mon Aug 29, 2016 7:50 pm

That looks positively professional compared to my very first effort Chris!

I started off with a crystal set (as most of us did). That didn't even have a chassis as such, just a 500pF tuning gang screwed to a piece of hardboard and everything else was mounted on the gang....it worked though....!

 
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Re: Back to basics...just for fun!

Post by Cathovisor » Mon Aug 29, 2016 8:10 pm

I recall that they taught that 'copper nails in wood' technique in my old school's electronics class back in the 70s. A subject I couldn't do, because - get this - I was deemed to be in too high a stream to learn a practical thing like that! Just like my brother wouldn't have been allowed to do technical drawing if he'd gone to the grammar school - he failed his eleven plus and luckily, the secondary modern taught TD. He went on to be a very successful architect!

 
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Re: Back to basics...just for fun!

Post by Katie Bush » Mon Aug 29, 2016 9:02 pm

Hi Chris,

Did you do the component layout over a copy of the schematic? - It just has that look about it.... :bba

 
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Re: Back to basics...just for fun!

Post by CTV » Mon Aug 29, 2016 9:33 pm

Not over a copy of the layout just wired it as I saw it, so copied in that sense yes. From above it looks sort of neat-ish but in 3-d Blughhh!!

AM_Transmitter.JPG

below.jpg

 
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Re: Back to basics...just for fun!

Post by sideband » Tue Aug 30, 2016 1:11 pm

CrustyTV wrote:I couldn't quite bring myself to destroy the poor creature so it sits dribbling in the corner of the workshop.


I feel the same. What I think I 'll do is find a small radio case to fit the original circuit into as it is and add a small amplifier to drive a speaker so it sort of shows then and now....

The quality of this little reflex set is surprisingly good so a decent IC output stage and a 4" speaker should sound quite good

 
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Re: Back to basics...just for fun!

Post by Pamphonica » Tue Aug 30, 2016 2:41 pm

Just a suggestion, but why not put it in a clear plastic box. Amaze the youngsters with what 2 transistors could do! remind them that their iphone cannot tune medium wave and still uses 2 billion transistors (iPhone 6)!!
Jeremy

 
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Re: Back to basics...just for fun!

Post by sideband » Tue Aug 30, 2016 4:00 pm

Pamphonica wrote: Amaze the youngsters with what 2 transistors could do!


I don't think many youngsters today would be amazed at what two transistors could do......there might be some interest if it could log into any radio station in the world and also give free internet access.........

 
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Re: Back to basics...just for fun!

Post by Pamphonica » Tue Aug 30, 2016 5:30 pm

I still get a suitable reaction when kids complete a crystal set - no batteries! - and tune in radio stations!
But maybe that's mainly with the sub-teen kids...

The same is, surprisingly, true for middle-aged chaps with no technical background doing the radio amateurs exam, which I teach on behalf of my radio club. The idea of such a small assembly of components doing anything like that is still a bit of a "Wow" moment, even in this digital age. The crystal set is part of the foundation and intermediate exams.

Jeremy

 
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Re: Back to basics...just for fun!

Post by Niall » Tue Aug 30, 2016 7:56 pm

In one of my junk boxes is a collection of pots held together with screened cables. It is the remains of my first major project, a stereo mixer. I think the box is still around too, salvaged from an old video game which was in a nice little sloping front case.
It did work but for some reason all the pots were incredibly noisy when moved even though they were new. I don't remember where the circuit came from or why I dismantled it. Maybe I'll see how much of it survives.


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