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Old 7th May 2014, 6:18 am   #81
audion_1908
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Default Re: Building a Radio from Junk

I have got some fibre board off a broken pallet for the radios base and back, very authentic and I need to keep these fingers out! there will be 250v dc HT in there!
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Old 7th May 2014, 6:32 am   #82
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Default Re: Building a Radio from Junk

I also have a Igranic midget audio 3.1 transformer in the post to rewind it and I will use it as a phase splitter for the set of output valves!
https://www.vintage-radio.net/forum/...d.php?t=105306
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Old 7th May 2014, 7:33 am   #83
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Default Re: Building a Radio from Junk

this is a basic plan of what the radio will look like!
speck
it will be a large and heavy cathedral radio, with 11 to 13 valves!
a dynamotor to supply only the audio output valves for upto 10 watts output!
all other valves will work with 24v for the HT
6 bands using switched crystals and a variable oscillator and 2 mixers
a nixie tube will show the band and maybe change brightness like a magic eye tube for tuning?
the tuning dial will be lit from behind threw a narrow slot and the dial will move when tuning
AGC
Bluetooth audio receiver for fun!
a lot of hand made components!!

I have put lots of new posts on page 4!
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Old 10th May 2014, 7:49 am   #84
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Default Re: Building a Radio from Junk

Quote:
Originally Posted by audion_1908 View Post
a lot of hand made components
homebrew FM Radio, also the coils are selfmade.
Now I have the audio stage and the IF Stage working, the next to do is the tuner

greetings from germany
Martin
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Old 10th May 2014, 10:43 pm   #85
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Default Re: Building a Radio from Junk

Your FM radio looks great, I would love to know more about how you made the IF coils?
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Old 11th May 2014, 7:39 am   #86
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Default Re: Building a Radio from Junk

For an FM IF strip, the transformers will be tuned to 10.7 MHz and will have a lot fewer turns than 455kHz types.

It looks like the one in Martin's photo which has its lid off is the discriminator transformer, and I suspect the twin valves next to it are EB91, otherwise known as 6AL5 !

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Old 11th May 2014, 8:00 am   #87
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hello,

thank you for interesting I am still working in the radio.

IF:
stage 1 = EF184
stage 2 = EF183
stage 3 = 6AK5 means EF95 7pin
ratio tube = 6AL5W (EB91, EAA91)

Audio: there is a EL84 , and I want to insert a driver, may be another 6AK5 to preamplifie the audio.

The old transformer delivers 210V~ and 6,3V~
After the Elko is aroud 260V DC to feed the EL84, from there a 910 Ohms and a smaller Elko to feed the IF, there are +200V at upside.

As rectifier it use 4 Diode.
For the solding I used tubular rivets in epoxy plates

The Coils are made on my small Drehmaschine (engine lath?), the diameter is 7mm, inside is a metric M4x0,5mm to hold ferrite screws from amidon Type F10

greetings
Martin
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Old 11th May 2014, 8:15 am   #88
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Default Re: Building a Radio from Junk

Interesting. The 6AK5 is in the same size envelope as the 6AL5. So it looks like I scored 50%.

Engine lathe is the true name, though few people know it. It's usual in English to say only 'lathe' and to make no discrimination of the many types. THis sometimes causes confusion.

Bill Amidon is a retailer of components (Otsego street, Hollywood if I remember right) The cores he sells come from Fair-Rite inc (Wallkill NJ) for ferrites, and Micrometals inc (Anaheim CA) for dust-iron parts.

David
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Old 11th May 2014, 8:28 am   #89
6AL5W-Martin
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hello David,

Amidon is one of the last who make and sell HF components like ferrite rings and screws.
F-10 means this is a ferrite what works allready in the area of 10MHz.

In calculating IF coils you must go with F a little higher to get the right data, a filter what is turned exactly following the calculation for 10.7MHz will go 9,9 to 10,3MHz only bec. there is some unknown C in the valves what adds to the 22pF of the coil... around 5µH will do.

a small ferrite screw, only 4mm in a 7mm coil, will give a high Q, but a small area of adjust.

greetings
Martin
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Old 11th May 2014, 9:52 am   #90
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Default Re: Building a Radio from Junk

Lower frequency parts have been getting harder to get. I think Audion is going to have to re-cycle IFTs from old raios.

Toko have obsoleter their S18 VHF moulded coils, so the threaded slugs for them (sold separatly in three different grades) are't going to be available any longer. I don't know whether they are still in TDK's cataogue.

There is one multinational distributor of magnetic parts which isn't generally known outside of commercial circles... Dexter Magnetics.

RS keep a few ferrite toroids (Fair-Rite products) and occasionally I've found one I needed.

In amateur radio circles we have a number of retailers who get supplies of the popular dust-iron and ferrite cores from the US and have trays of them on display at radio rallies. These are usually Fair-Rit and Micrometals parts but are usually labelled with the Amidon versions of their part numbers (rather similar to the Fair-rite numbers). Try JABDOG's website.

Back to 455kHz for AM, and the stated requirement that only re-cycled junk parts can be used... I think that limits it to recovered 455/465kHz IFTs. For usable stability, it needs to be dust-iron or else gapped ferrite cores and there aren't any other users of these things in large enough quantities for there to be a chance of finding scrap containing them.

Siemens used to have a superb range of pot cores in many sizes, materials and gaps, but I see few arond now. Electrovalue used to be a frienly retailer with good stock but they've gone now. With gapped pot cores you used to be able to insert adjusters and get something like +4 to +7% inductance. (always positive, of course.

David
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Old 11th May 2014, 12:03 pm   #91
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Default Re: Building a Radio from Junk

I will use working if transformers in the prototype to test the circuit, but for the junk radio build I will only use junk if transformers, that need fixing, or build them, I am looking for a good if to use as my gold standard, I have been thinking of maybe using fragments of broken ferrite rod or ring, or air core
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Old 11th May 2014, 12:39 pm   #92
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I am on my way to NVCF looking for IF transformers and to pickup some valves!
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Old 11th May 2014, 1:49 pm   #93
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The other way for IFTs are fixed (air cored) coils and trimmer caps. Old TVs have an abundance of IF cores etc. too, and old dual standard valve jobbie would yield many.
 
Old 11th May 2014, 9:28 pm   #94
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Default Re: Building a Radio from Junk

Good find! Skips ain't what they used to be so you've done well there. The tweeters are a version of the ubiquitous Audax FDW-10. These are very good for a tweeter Maplin's were selling for less than £2 each by the time production ended. According to the spec sheet for these, they top out at 23kHz! I've used them on various projects over the years and I've always found them to be completely happy with a capacitor instead of a full - on crossover network.

Regards,
Paul
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Old 13th May 2014, 12:32 am   #95
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Default Re: Building a Radio from Junk

IF transformer cores aren't ferrite. They are an ultra-fine iron dust combined with a binder material.

Ferrites are higher permeability and higher temperature coefficient, so for resonator use they are used as gapped cores where the gap dominates (and stabilises) the overall permeability of the core. Unless you chose a good gapped pot core, a ferrite-based IFT would be too temperature sensitive for easy use.

David
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Old 13th May 2014, 7:01 pm   #96
6AL5W-Martin
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Default Re: Building a Radio from Junk

here in germany is a little manufacturing what still build a series of IF transformers for homebrew tube radios. So they are to get. Google will find them by "Reinhoefer"

greetings
Martin
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Old 27th May 2014, 3:17 am   #97
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Thanks for the info but I feel it would be cheating a bit to use them in this project
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Old 27th May 2014, 11:28 pm   #98
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Default Re: Building a Radio from Junk

There were a number of tubes here developed for auto radios that used 12VDC filaments and 12VDC on the plates.
They worked quite well. I have repaired a number of the radios that used them over the years.

The farm radios here that used 32V are findable, but not too sought after, due to the fact they run on 32V. I have one in the restoration que here, an old Delco.

Years back I did build a 32VDC supply using IC regulators for the B+ and C+ voltages, and batteries for the filaments. I cheated by using 36VDC from the lawnmower batteries, and a 4V fil tube as a dropping resistor. (Be sure to check the filament current draw so it doesn't exceed the fil. current of the dropper tube.) Good use of an old "junk" TV series filament tube.
One of the radios I rebuilt for a customer had "built in" bias packs and an 1.5V audio bias battery too. The local battery store was able to make what I needed up for the "C" battery pack, which was soldered into the radio. That radio was more sensaive and selective than any AM radio I ever had!
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