Reply With QuoteI wouldn't use a square wave generator! The output is loaded with harmonics (that's the characteristic of a square wave). You need something that generates a good pure sine wave.
@ techiesteve -- Would this circuit serve as a signal generator?oscillator.jpg
EDIT: Sorry about the double post.
Last edited by SharpyWarpy; Mon 28th Nov 2011 at 01:18. Reason: double post brain flatulance
I wouldn't use a square wave generator! The output is loaded with harmonics (that's the characteristic of a square wave). You need something that generates a good pure sine wave.
73
Pat K7KBN
Semper ubi sub ubi.
Well how about this one?Originally Posted by K7KBN
single-op-amp-sine-wave-generator.gif
Might be ok for audio. What if you need an RF signal?
73
Pat K7KBN
Semper ubi sub ubi.
The UPC20 is also available from Littlediode in the UK, same price. The NTE branded components are common in the USA. They are either the same part or a close equivalent. Yes, the circled numbers you mentioned are the typical voltages to be found when correctly working.
The LM386 is a common audio amp IC that needs minimal external components and is cheap to buy. In your circuit it's used as an oscillator. It would need a potentiometer, as the volume control in the radio, to reduce its output. This IC would also be an ideal choice for a replacement amplifier. The web is full of circuits using this.
An audio IC will normally draw minimal current, known as quiescent current. This will rise as volume is increased. The quiescent current shouldn't be so high that the pilot bulbs dim. I suspect this is why the previous owner cut the supply track to the IC. You could switch your meter to DC current (check, you may have to change sockets depending upon your meter), and use a high range first, place it across the cut track to monitor the current being drawn by the UPC20.
Although the chances are the audio IC has failed, I'd check the components around it first. I'm sure you mentioned a meter needle earlier, if so an analogue meter isn't suitable for checking resistors in circuit, a DVM would be. Check the electrolytics too.
Now it's time for me to head of to work, another busy day.
Steve M0SVB
Okay what about the one at this URL:
http://www.electronic-circuits-diagr...torsckt1.shtml
That little circuit would be OK for the IF section, provided the ceramic resonator is on the same frequency as your IF in the receiver. That just leaves the RF section. You should be able to buy a simple signal generator quite cheaply, I've got a couple here that I use sometimes for using on jobs like you have there, one is an old valve Taylor Instruments, it is a bit wobbly, but that doesn't matter much for what I use it for plus a solid state one. Both these generators also put out an audio tone as well.
I was trying to work out where you are located, are you in the UK or US? The reason I ask, if you are in the UK then I'll try and point you in the direction of a generator.
Thanks for that information. I do have a digital multimeter. I have a very old Realistic multimeter too, but I never use it any more. I did a test for current draw and it is 860ma. Wow! Now, about checking the electrolytics, would I be checking them for short circuit? Isn't that about the only kind of test that can be done on those in circuit? I'm not sure. I don't have any formal training in electronics. I do have a feature on my MM that measures the capacity of a capacitor but of course I'd have to take each cap out one at a time.
@ G4LNA: I edited my profile to show my location. Thank you for your offer on the generator but there's a lot of water between us. :*)
I checked the resistors and the values are good. The caps, none are shorted. Voltage at the voltage regulator circuit for amp is 10.9. So I think the amp chip is bad. Especially since it was drawing 860ma when it was connected. Now I'm torn between replacing the chip with an NTE1075A -- thus leaving the set almost factory original -- or making my own audio amp with the LM386 and a gain of 50. Attached is an image of the LM386 amp circuit with a gain of 50. I tested the gain pot on the set and it tests good. It's a 5k pot. So I'm going to use that instead of the 10k pot shown in the image.amp_for_dx160-014.jpg
I'm still wondering though if 50 is too much or not enough gain. If it is too much I can install a resistor on the input.
I am going to start a new thread in the "Home Brew, Kit Building & Mods" forum and pick up there with the amp build process. I'll post the URL here after I do that.
OKAY: Here's the URL to the new thread continuing what has evolved into something entirely different from the original topic:
http://www.hamradioforum.net/threads...-audio-amp-mod
Last edited by SharpyWarpy; Tue 29th Nov 2011 at 01:18. Reason: Inclusion of new thread URL
An audio and RF signal generator is the preferred tool, I use both here, but in this instance all that is needed is something simple that will output audio and RF for basic tests, 'is this stage working'. Here the sharper the rise time of the square wave the better, there will be harmonics from AF to RF. We aren't aligning or conducting tests on distortion. Years back simple signal injectors mounted in a tube with a probe at the end were very popular, and effective for simple testing. I built 2, one using a couple of transistors, another used a 555 chip.
As of now, it looks as if the UPC20 is defective.
Steve M0SVB
Thank you for your reply, techiesteve. I've been looking around for a signal generator to build. It seems I've acquired a bigger interest in radio now so I'll need a signal generator and I'll need to do a lot of studying on the subject of radio in general. When I picked this old receiver up I never suspected I'd be introduced to the world of radio. I'm completely overwhelmed with my lack of knowledge. I remember as a child a friend of my dad's was into ham radio big time. I used to love going with my dad to his house. He was always in the back yard in his radio shack. Had tons of equipment and I could tell he loved radio. He'd tell us about how he talked to people in Australia sometimes. To me it was all just so awesome. He had an antenna in his yard that would be the envy of any ham radio operator today, I'm sure. It was a triangular shaped framework about a foot wide at the base and was in two parts, the top part could be raised and lowered. It was mounted on a big concrete pad with guy wires all over the place holding it in place. All of it made a big impression on me. I remember once he was giving me a lift home and had the car radio on -- just a normal radio. He'd slow down and tell me "listen to the volume change right here" and it would go down. Then he'd inch the car forward until the volume started picking up again. "Hear that?" he said. "That's the nature of the wave." And he would go a little bit farther into it trying to help me understand. I think he knew way back then I had a love for technical stuff like that. Like he did.
Yes, that isn't exactly local is it?
Unless of course you can wait till next year when we come over to the sunshine state.
LOL, you're right. Not exactly local. Nevertheless, a nice gesture on your part.Yes, that isn't exactly local is it?
Unless of course you can wait till next year when we come over to the sunshine state.
I have decided to get the replacement IC, the NTE1075A, from Mouser. I'll just have to wait until I have the money. None of the caps are shorted and the resistors check out fine. I'll probably wind up replacing all the caps anyway though.
Sharpy, your trying to induldge a high tech hobby that requires you to know the basics of electronics.
Without the basics you will often get discuraged at the lack of sucess by guessing what your trying to do.
Very first thing you need to learn is how to read the schematic and understand what your looking at.
For example, do you recognize the audio circuit so you can test it for operation?
Can you recognize the RF stages, the IF stages and what they do?
I'm not trying to give you a hard time but to show what you need to have in order to enjoy what your trying to do.
Good luck.
Thank you for your reply. I have some basic knowledge of electronics. No formal education, just basics I have gleaned from libraries and the internet. I know enough to read a schematic and recognize the audio circuit. My prior posts contained information to that effect. I have bypassed the on board audio circuit with an external audio circuit and tuned in many broadcasts on at least two bands. Recognizing the RF and IF stages is something I have yet to understand but I have been studying that. If I may make a point here, this is the purpose of these types of forums. To help each other learn -- at least to point someone in the right direction to acquire the knowledge necessary to fully enjoy the hobby, whatever it may be -- electronics, bicycling, snorkelling, making your own beer, etc. So far I have studied a bit from the Wiki encyclopaedia and a couple other places. Now, all that being said I believe I have spent enough time listening to various broadcasts (some even out of Bejing China, but in English) to know radio communications is not my cup of tea. I like to say you never know until you try, and give it a thorough try. I'm satisfied and if anybody wants this receiver I'll be happy to let them have it for parts. If said person is willing to pay the shipping. The audio circuit is fried. The RF gain pot is bad, but a good shot of electronics grade silicon spray might cure that as it is a bit stiff. Another of the pots is like that too, I can't remember which at the moment. At any rate a simple change of pots is not a difficult job for someone who would get more pleasure out of this unit than I would.
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