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Old 24th Feb 2021, 2:05 pm   #21
lightning
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Default Re: Pocket radio repairs

Classic Gold AM is quite good round here, their website says 1458 AM

The station is loud enough, distortion is not like a faulty speaker, it's more like a faulty amplifier would sound.

But on R5 it plays fine at low volume. Shame l can't post an audio clip of it.

The trimmer on the tuner will peak the signal at 1458, it comes in louder but with the same distortion.

Maybe l should try the detector diode as suggested. Will one out of another similar set do?

Last edited by lightning; 24th Feb 2021 at 2:12 pm.
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Old 24th Feb 2021, 3:34 pm   #22
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Have you a way to inject an audio signal into the volume control? That way you could rule out RF/IF stages or Audio stages that is causing the fault.
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Old 24th Feb 2021, 7:04 pm   #23
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can you check the voltages on the transformer nearest the output transistors, note! voltages measured from the poss side of the battery, Do you have a circuit. Mick.
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Old 24th Feb 2021, 7:27 pm   #24
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Not going to be exactly the same but probably similar if no circuit available.
http://fourier.eng.hmc.edu/e84/labs/radio.gif
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Old 24th Feb 2021, 8:55 pm   #25
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Thank you l will get on to this and report back.

Also

l think it's time to buy a signal injector!
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Old 25th Feb 2021, 10:13 am   #26
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ls the detector diode anything special or will any small diode do the job?
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Old 25th Feb 2021, 10:25 am   #27
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Hi have you checked the diode , it should be a Germanium type, Mick.
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Old 25th Feb 2021, 3:18 pm   #28
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ls the detector diode anything special or will any small diode do the job?
Any small germanium should do the job. Nothing special at all.
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Old 25th Feb 2021, 10:59 pm   #29
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Thank you for the information, l will let you know how l get on with it.
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Old 26th Feb 2021, 12:03 am   #30
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Hi what makes you think the diode is at fault? Mick.
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Old 26th Feb 2021, 12:39 pm   #31
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On a previous post someone said the detector diode could be faulty and it receives strong stations but not weaker ones, it's something l could try in the absence of any test equipment to diagnose the fault.
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Old 26th Feb 2021, 1:18 pm   #32
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Mick suggested some voltage readings be taken, I would do those first.
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Old 26th Feb 2021, 8:12 pm   #33
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Yes will do, will get on to it this weekend
lt's a steep learning curve.
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Old 27th Feb 2021, 8:27 am   #34
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Default Re: Pocket radio repairs

Does the detector diode on a set like this have to be germanium? What happens if a silicon one is used?
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Old 28th Feb 2021, 7:58 am   #35
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Not thought about it but it would depend on the silicon diode. A 1N4001 will be different than say a fast acting diode, the conduction voltage is different with silicon being around 0.6v and germanium 0.2v so the germanium will be more sensitive. The junction capacitance will have some effect, presume a germanium will be less but I have not checked.
I am not a designer so I tended to replace like with like unless it was obvious a more suitable part was available.
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Old 28th Feb 2021, 8:30 am   #36
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Not thought about it but it would depend on the silicon diode. A 1N4001 will be different than say a fast acting diode, the conduction voltage is different with silicon being around 0.6v and germanium 0.2v so the germanium will be more sensitive. The junction capacitance will have some effect, presume a germanium will be less but I have not checked.
I am not a designer so I tended to replace like with like unless it was obvious a more suitable part was available.
Not a power rectifier diode, a small signal diode like a 10D4.
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Old 28th Feb 2021, 8:51 am   #37
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I have probably got the wrong data sheet but the 10D4 appears to be a rectifier for 50/60 Hz. It’s needs someone better than me to give a conclusive answer but for me junction capacitance and forward turn on voltage are the important specification. Small signal diodes such as 0A91 are germanium (0.2v) point contact ( low capacitance).

https://www.digchip.com/datasheets/p...2/10D4-pdf.php
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Old 28th Feb 2021, 9:35 am   #38
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Originally Posted by Nuvistor View Post
I have probably got the wrong data sheet but the 10D4 appears to be a rectifier for 50/60 Hz. It’s needs someone better than me to give a conclusive answer but for me junction capacitance and forward turn on voltage are the important specification. Small signal diodes such as 0A91 are germanium (0.2v) point contact ( low capacitance).

https://www.digchip.com/datasheets/p...2/10D4-pdf.php
Possibly my mistake naming the 10D4, but at any rate, a small silicon signal diode.
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Old 28th Feb 2021, 9:37 am   #39
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See what others members can explain.
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Old 28th Feb 2021, 10:44 am   #40
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Can someone recommend a suitable germanium diode that l can buy online, that will do the job on this radio?
Or sell me a couple?
l've got plenty of random diodes on circuit boards and in boxes of components but no idea which are germanium.
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