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telefunken: 8U; Gavotte

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » telefunken: 8U; Gavotte
           
Timothy Maslyn
 
 
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22.Sep.10 02:17

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I am restoring this radio and have run into a problem that eludes me. I am hearing audio distortion using the FM band that does not appear when in the AM band. I have replaced most of the caps in the radio, aligned the IF, both by ear and by using a signal generator and scope. Sensitivity is on par with a working Gavotte 7, which I use as a base line model. Can anyone suggest where to look for the distortion? I have been told not to touch the RF amp if it is working.

Tim Maslyn, Spring Hill, Florida

352-688-5630

iss[A*T]netacc.net

Bernhard Nagel
Bernhard Nagel
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27.Sep.10 17:06

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Hi Timothy,

did you minded the electrolytic capacitor (2 µF) located inside of the last IF can? It's where the EABC80 sits. These small elec. caps are prone to get dried, a proper FM alignment is impossible when this happens. The center tuning point is not clear and often distorted.

One can measure this capacitor without opening the can. Just connect an accurate capacitance meter to pin 3 and ground. A new 2.2 µF cap can be soldered in parallel to the old (defective) one outside of the IF can. The positive pole is grounded.

Last IF can (with EABC80) viewed from the downside

(Excerpts from the German model Gavotte 8 where complete documents can be found.)

Best regards
Bernhard

 

 

Timothy Maslyn
 
 
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11.Oct.10 18:00

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Mr. Nagel,

Thanks for the direction. I have been very busy with work and had not checked for the response. I found that the tuning was off, and needed a better voltmeter for alignment. Have now received a VTVM and will do a better job at aligning.

Stuart Matousek
Stuart Matousek
 
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11.Nov.10 14:06

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I have been reading up before I tackle the tuning circuits on my radios and learned a few things which may be relevant to this. Is the distortion on all fm stations? if it is only on the strong stations it could be due to inadequately functioning AGC. It can also be a manifestation of some broadcast quality, some commercial stations in the UK do not work well on the old radios wheras BBC does as the quality of the modulation is better. Theres a way this can be remedied. Theres a very good set of articles i found on the internet on radio repair which explains this. I dont have the refference with me now, ill try to remember to find it.  

  
rmXorg