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Author Topic: Yo................ Vincenzo.......................  (Read 171259 times)
AC5UP
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« Reply #210 on: November 29, 2012, 07:54:45 AM »

It's possible to do an alignment with just a CW carrier, but the problem is in knowing when you hit a peak or null. Oscilloscope on the coil side of the detector diode(s) can show you, but then you're aligning to an abby-normal condition. Chances are the 'scope load won't matter but in strictest terms the 'scope input becomes part of the IF and when you remove the probe.......

There's also a chance the radio was stagger-tuned and that's why it sounds good. Unless you know how to do that (look it up!) you're better off to leave it alone.
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N4NYY
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« Reply #211 on: November 29, 2012, 12:08:11 PM »

It's possible to do an alignment with just a CW carrier, but the problem is in knowing when you hit a peak or null. Oscilloscope on the coil side of the detector diode(s) can show you, but then you're aligning to an abby-normal condition. Chances are the 'scope load won't matter but in strictest terms the 'scope input becomes part of the IF and when you remove the probe.......

There's also a chance the radio was stagger-tuned and that's why it sounds good. Unless you know how to do that (look it up!) you're better off to leave it alone.


I did track down the problem in the audio oscillator. I seem to have the RF and Carrier, but the modulation is not there. I may just buy a bunch of transistors and start shotgunning it, as I do not have the time to play with it. There seems to be nothing much to it. Schematic has voltage markers.
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N4NYY
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« Reply #212 on: November 29, 2012, 12:17:29 PM »

While I have you, I want to pick your brain again. I also replaced the caps on that GE P975B that I picked up for $5, and wala! It came to life! And sounded great!

However, the 4 AA batteries were and extra tight fit. They almost seemed too long. The case asks for Penlight. The fit is so tight, that the terminal is not making a full contact. Were Penlghts different and smaller in the 1960s?
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AC5UP
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« Reply #213 on: November 29, 2012, 02:54:45 PM »

Were Penlghts different and smaller in the 1960s?

Not that I recall, although I don't think the alkaline battery had become a common item. Just for grins I looked it up, LIKE YOU COULD HAVE DONE, and according to the inner-web 'Penlight' is the generic name for an 'A' series battery. AA, AAA and AAAA are all considered penlight batteries.

Given the age of the radio, the battery holder you have might not be original or the exact right size. I never liked those holders as the ends would crack loose and then you had volts spilling out of the radio........
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N4NYY
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« Reply #214 on: November 29, 2012, 02:56:27 PM »

I found the biatch in the E-200D. In the cal procedure, they call for the audio oscillator to be at 1.3 Vrms at a certain test point. I found that 1.3 is too close to the fence. A little drift downward, and the oscillator drops out completely, and then no modulation. That is what  get for following the book. I bumped it up. If that craps out again, I will bump it up more.

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N4NYY
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« Reply #215 on: November 29, 2012, 03:00:49 PM »

Were Penlghts different and smaller in the 1960s?

Not that I recall, although I don't think the alkaline battery had become a common item. Just for grins I looked it up, LIKE YOU COULD HAVE DONE, and according to the inner-web 'Penlight' is the generic name for an 'A' series battery. AA, AAA and AAAA are all considered penlight batteries.

Given the age of the radio, the battery holder you have might not be original or the exact right size. I never liked those holders as the ends would crack loose and then you had volts spilling out of the radio........


I actually did before I asked you. Wiki said Penlight was another word for AA.

http://en.wikipedia.org/wiki/List_of_battery_sizes
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AC5UP
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« Reply #216 on: November 29, 2012, 03:11:32 PM »

BTW:  It has been said that anyone who remembers living in the 1960's wasn't really living in the 1960's........

All I remember is the first Earth Day and that I had to work on the weekend of Woodstock. At the time Woodstock wasn't a big deal because most of the bands scheduled to play hadn't become familiar names. Sha Na Na played Woodstock, fer' chrissake, so it wasn't all A-List performances:  http://www.woodstockstory.com/bandsperformerssetsplaylists1969.html

( my apologies to Bowser if you're reading this, but at least you weren't in The Incredible String Band )

IMHO any band that calls themselves incredible probably isn't.   Tongue
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N4NYY
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« Reply #217 on: November 29, 2012, 06:01:23 PM »

HOLY RADIOWAVES, BATMAN!

I got the RF generator working. I then proceeded with the Zenith 755M alignment. As you said, alignment was fairly close with a hint of fine tuning done (wife almost hit me with a bat because of the constant tone).

So, I then take the radio upstairs to make a run thru the dial. I only got to 760 because I got too excited!

On first pass:

WGR 550 Buffalo
WHEN 620 Syracuse
WLW Cincinnati
WGN Chicago
WJR 760 Detroit

At that point I stopped and came downstairs to type this.


DING DONG, THE WITCH IS DEAD !

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AC5UP
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« Reply #218 on: November 29, 2012, 06:52:17 PM »

What?  No signal from WSB in Atlanta on 750 ??   50 Gallons non-directional at night and you can't hear it ??  Tsk.

Even I can do that most nights, despite a local on 740..........  Try not to wet yourself when you hear CKLW on 800.
There's a nighttime lobe in your direction:  http://radio-locator.com/cgi-bin/pat?call=CKLW&service=AM&status=F&hours=N

BTW:  Common trivia question... CKLW is in Windsor, Ontario just across the river from and south of Detroit. That's right, geography fans, if you travel due south from the City of Detroit you're in Canuckistan.   Tongue
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AC5UP
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« Reply #219 on: November 29, 2012, 09:19:10 PM »

So last night I wound a coil for the crystal set project... Nothing fancy, junkbox mystery toroid and insulated 20 ga wire. Just for grins I set it up quick & dirty on the bench with the 'scope as a modulation detector. Damn thing works pretty good looking at the RF envelope. Doesn't tune the entire band, but catches a good chunk of it including the stations I'm interested in.

So I decide to add a diode. Nearest thing within reach is an LED.

Worked like a champ..............   Grin
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N4NYY
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« Reply #220 on: November 30, 2012, 06:05:25 PM »

LED detector! LOL. What ever works.

This 755M picks up NYC stations as if I was sitting in midtown.
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AC5UP
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« Reply #221 on: November 30, 2012, 06:32:56 PM »

Think of all the money you'll save on carfare...........

BTW:  In some cases I can get real creative on parts selection. We all know a Germanium diode has the lowest forward voltage drop so that's what we want in a low-level stage like a detector. Fair enough. But how is it that many radios used a TUBE detector with a forward drop many times higher than an LED ??

Ja..... Properly biased they had no forward drop and could sound better than a 1N34A.

An LED is just a diode, but with a brighter future than others................    Roll Eyes
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N4NYY
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« Reply #222 on: December 08, 2012, 06:18:22 PM »

OK. Bored with this so, I am unloading it for a collector:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190767774550
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AC5UP
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« Reply #223 on: December 09, 2012, 08:35:53 AM »

Very nice... The pictures look good and definitely reinforce the claim of like new condition.

But.   You missed one thing:   http://i224.photobucket.com/albums/dd78/yankees_1996/IMG_2598.jpg

The top cover has a bow in the middle.  Straightening it would have been a 10 second job when the cover was off the chassis.

I give this exercise two gold stars and one tsk.  Coulda' been three gold stars, you were that close................   Roll Eyes

BTW:  If you feel like playing, here's an experiment for you:  With a favorite weak station tuned in, try sliding the two-turn winding on the ferrite bar to one side or the other to see if the signal improves. Chances are it will, as that's how you peak most ferrite bar antennas.  Tune a station at the low end of the band then slide the windings until you find the sweet spot.

Also, I have been tinkering with crystal sets and found that using insulated wire for the coil makes a huge difference. The insulation spaces the windings to improve the Z of the coil and I'm seeing better than 800 millivolts of RF (P-P) on a local station with 20 feet of wire as the antenna. The same coil with close-wound enameled wire barely made 200 millivolts. Next step will be to wind a coil with fishing line between the turns for even wider spacing.

RCA used to spread out the windings on their early ferrite bar antennas and use the entire length, so it's not like I discovered anything. Just confirmed that an old idea still works. Newer designs use a close-wound coil that occupies maybe a quarter to a third of the bar and can slide to the sweet spot.
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N4NYY
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« Reply #224 on: December 09, 2012, 05:06:17 PM »

Ugh. Had to add chassis shots because someone said I was asking a premium and wanted to see chassis shots of my work. Well, see for yourself.
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