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Old 20th Jul 2017, 2:52 pm   #41
ms660
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Default Re: First Radio Build - 12V HT system

There's three connections to the pot, the pot will have three tags, the center tag is the wiper (black arrow in the schematic) the two outer tags are the track (50k in the schematic) The regen pot in the schematic is configured as a potential divider, the track is connected across the supply, one end to the 12 volts +ve rail, the other end to chassis/ground rail which is also the -ve of the supply voltage. The slider connects to the 100k resistor.

Lawrence.
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Old 20th Jul 2017, 3:24 pm   #42
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Default Re: First Radio Build - 12V HT system

Quote:
Originally Posted by ms660 View Post
There's three connections to the pot, the pot will have three tags, the center tag is the wiper (black arrow in the schematic) the two outer tags are the track (50k in the schematic) The regen pot in the schematic is configured as a potential divider, the track is connected across the supply, one end to the 12 volts +ve rail, the other end to chassis/ground rail which is also the -ve of the supply voltage. The slider connects to the 100k resistor.

Lawrence.
Stupid mistake, I didn't see the 12V line somehow. I'll get a picture of the board up when I finish it.
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Old 20th Jul 2017, 7:32 pm   #43
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Default Re: First Radio Build - 12V HT system

I wound the coil a second ago but some wires are crossed over and there are some gaps in between. Will this still work ok or should I start again?

Cameron
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Old 20th Jul 2017, 9:58 pm   #44
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Default Re: First Radio Build - 12V HT system

It'll probably work; but will you ever be truly happy, knowing you might have been able to wind that coil more neatly?

Don't rip your first effort apart, though; make a new former for your second attempt, just in case it's no better than the first.
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Old 20th Jul 2017, 11:24 pm   #45
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Default Re: First Radio Build - 12V HT system

That's true, I'll give it another go at some point but I'll probably just test it out with this one. Winding that wire is a bit of a pain. I ended up breaking off the tap as well so I had to solder it back on, not a particularly neat job

Cameron
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Old 21st Jul 2017, 11:41 am   #46
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Default Re: First Radio Build - 12V HT system

Another question! What are those connections on the valve like the ones with the number 9 that seemingly go nowhere? I have attached another diagram with a non transparent background.

Cameron
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Old 21st Jul 2017, 11:51 am   #47
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Default Re: First Radio Build - 12V HT system

That's because pin 9 isn't connected to anything when the heaters are connected for 12.6 volt operation.

Remember that the ECC82 valve heaters can be connected for 6.3 volt or 12.6 volt operation.

For 6.3 volt operation pins 4 and 5 are connected together, the heater supply is then connected to that connection and pin 9.

When connected for 12.6 volt operation the heater current will be half current that is drawn when they are connected for 6.3 volt operation:

http://www.r-type.org/pdfs/ecc82.pdf

Lawrence.
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Old 21st Jul 2017, 12:15 pm   #48
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Default Re: First Radio Build - 12V HT system

Ah of course! Thanks for the valve schematic I was just going to look for one. I'm building a case just now while I wait for the last few components to arrive.

Cameron
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Old 22nd Jul 2017, 10:49 pm   #49
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Default Re: First Radio Build - 12V HT system

Here are some pictures of the build so far. I decided to use the speaker from a 1980's sony bookshelf speaker and decided just to use the cabinet as the cabinet for the radio, it's going to be a bit crowded but I think I can fit it all in. Should there be anything I avoid putting too close together to avoid interference? Im not the best at woodwork so it looks home made of course but I'm fairly happy with it, after a bit more work it should look acceptable. The pots are not attached yet by the way.
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Old 25th Jul 2017, 11:55 pm   #50
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Default Re: First Radio Build - 12V HT system

I got all the wiring put together today but it's not working, the valve glows but nothing else happens. When I switch it on and off there is a crack but that is all the signs of life it's giving. I have had a check over my(messy) wiring and can't see anything obviously wrong. Is there something I could touch to make a sound or any tests I can perform? Also I must add this was done without an antenna but I would expect to hear some sort of hum. Thanks,

Cameron

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Old 26th Jul 2017, 4:06 am   #51
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Default Re: First Radio Build - 12V HT system

Standard advice is usually to start at the speaker and work backwards! In this case, though, I would suggest a binary search -- i.e., start in the middle. Disconnect the 10μF and feed an audio signal to the volume control. Does it come theough the speaker?
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Old 26th Jul 2017, 9:08 am   #52
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Default Re: First Radio Build - 12V HT system

Thanks for the advice, this will give me a chance to use the audio part of my signal generator though I don't know if it even works. If not I'll just get a 3.5mm aux cable and use the wires inside. I do get the suspicion however that it is more radio centric but at least this test will rule out the amplifier.
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Old 26th Jul 2017, 9:01 pm   #53
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Default Re: First Radio Build - 12V HT system

I have given that a shot and no sound is heard, I assume this means I work forward towards the speaker now but I don't know the tests I should perform. I would like to test the amplifier itself but I'm not sure how to do this.
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Old 27th Jul 2017, 10:44 am   #54
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Default Re: First Radio Build - 12V HT system

Hi,

I have one of these sets working on the bench at the moment and the little amplifier chip is difficult to work with being small and fiddely.
No sound from speaker? I would first check that you have a supply going into the chip from the battery. This should be on pin 4 & 6 of the chip and the + of the battery should be on pin 6.
Its surprizing how often the supply to the chip gets forgotten. I do it on a regular basis and then wonder if the sound I am hearing is a background hiss or just hairs growing in my ears
You will get lots of help on here and I suspect you will soon have it up and running.
Paul.
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Old 27th Jul 2017, 4:31 pm   #55
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Default Re: First Radio Build - 12V HT system

I'm fairly sure I have the power connected but I will double check later. I'm going to recheck all the wiring and resolder any dodgy looking bits. Thanks for the help,

Cameron
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Old 2nd Aug 2017, 12:58 pm   #56
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Default Re: First Radio Build - 12V HT system

I finally got the chance to have a good look at this, I realised I had connected both positive and negative ends of the amplifier to positive! Anyway with that problem fixed the radio still behaved in the same fashion. I decided to try injecting an audio signal again. With the auxiliary cable soldered to the two end pins of the volume potentiometer no sound was heard. I then played around a bit and got sound by connecting the end of the pot that goes to the 10uf resistor to one side of the speaker(the side that goes to -ve) and keeping the other side connected to the pot. I don't think it was amplified but I don't know it's probably a bit of a big speaker for this purpose. I can't figure out exactly why that happens so hopefully one of you can explain it.

Cameron
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Old 2nd Aug 2017, 1:27 pm   #57
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Default Re: First Radio Build - 12V HT system

With everything connected as designed, measure the DC voltages on pin5, pin6 and pin7 of the LM386.

Lawrence.
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Old 2nd Aug 2017, 3:41 pm   #58
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Default Re: First Radio Build - 12V HT system

Here are the measurements.

Pin 5 - 0.60V
Pin 6 - 12.27V
Pin 7 - 6.36V
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Old 2nd Aug 2017, 4:33 pm   #59
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Default Re: First Radio Build - 12V HT system

Pin 6 looks ok, I'm not sure what the voltage on pin 5 and pin 7 should be as I'm not familiar with the IC but hopefully someone else will be.

Also it's always worth checking over all the connections/components etc when doing a build.

Lawrence.
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Old 2nd Aug 2017, 4:59 pm   #60
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Default Re: First Radio Build - 12V HT system

Ok hopefully someone will chime in. It was very late at night when I finished it so it's possible there are more mistakes, I have checked over roughly but still need to go through with a fine tooth comb and make sure everything is right.

Thanks for your help,

Cameron
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