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Tone Potentiometer Restoring

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » Tone Potentiometer Restoring
           
Roberto Licandro
Roberto Licandro
 
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16.Sep.18 19:04

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Dear RMorg members, 


I am restoring a Saba Phono Super 9 radio and I have to replace the potentiometer of the bass tone control that of 3 + 3 MOhm Log that i never seen before, i do not know how it works and i did not found a description in the Web,  also in the electric schema it is represented with a different symbol (photo attached).

I have done a lot of research on the web to find a potentiometer like that, but unfortunately I have only found logarithmic potentiometers of at most 1MOhms or linear ones of 2.5 or 5 MOhm that I do not know if they can fit  anyway. 

If someone could advise me where to buy such potentiometer, even second hand, or could give me some suggestion to try to repair the existing one, or alternatively find a solution to get around the problem, I would be very grateful. 


Thank you in advance for the attention


Roberto 

This article was edited 17.Sep.18 08:55 by Roberto Licandro .

Kazmer NAGY
 
 
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17.Sep.18 11:32

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Can you explain, what is the problem with the potentiometer?

Roberto Licandro
Roberto Licandro
 
CH  Articles: 56
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Pict.: 433
17.Sep.18 16:41

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Kazmer first of all thank you for your attention,

when I turn the knob counter clockwise (pls. refer to the picture)  until reaching the end of the stroke the sound is enough clear and strong, while when I rotate clockwise the sound weakens until it almost disappears and s at the end of the stroke it is very weak and distorted.

I checked the values of the resistors and capacitors connected to the potentiometer and they all look correct, pls. find the schema in the picture. 


I have also measured values of the resistence of the potentiometer and of the voltages that i reported in the attached picture, and franckly for me are not clear at all.

Thanks a lot

Roberto

Bob Albert
 
 
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18.Sep.18 03:51

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It is unclear where the voltage originates.  The diagram you provide is both incomplete and hard to read.

 

I don't think there should be any direct voltage on this control, but I may be wrong.

 

Bob

Roberto Licandro
Roberto Licandro
 
CH  Articles: 56
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Pict.: 433
18.Sep.18 12:21

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Dear Bob,

many thanks for your doubts about the presence of voltage in the potentiometer. So I checked the circuit more carefully and I immediately discovered and replaced the faulty component and now it is all right: it is the capacitor shown in the image that is at a loss.

In any case I did not understand the values of the measuruments of resistence I did on the potentiometer that misled me.

Many thanks again for your precious contribution.

Roberto

This article was edited 18.Sep.18 12:29 by Roberto Licandro .

  
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