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Craftsman - Record-0-Matic

Discussion in 'Tuners' started by andreidaniel, Apr 16, 2018.

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  1. andreidaniel

    andreidaniel Member

    Messages:
    55
    Hello! One month ago I bought from somebody this radio cassette https://www.radiomuseum.org/r/craftsman_record_0_matic.html . Theoretically works pretty good on AM, Tape and a little bit on FM. The AFC also works.

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    Here is the diagram from the interior ticket:
    [​IMG]

    The radio cassette has a hybrid design with both Si and Ge transistors.

    The minor problem is a screw that is locked and when I tried to rotate broke down. The big problem is that even if is on tape or radio, the device makes from time to time an unusual noise; even if it is on low or higher volume. I tried to change most of the capacitors but in vain. Even the power socket I change, also in vain. I tried to power it from 9V battery but the same noise appear. I cleaned the rec-playback switch and the potentiometers but in vain.
    https://vocaroo.com/i/s0K8qYqNnINd

    Note:
    -at the end of volume potentiometer if I collect the signal to an external amplifier there is no such noise;
    -also at the colector of TR104 if I collect the signal to an external amplifier there is no such noise.

    What should I do?
     

     

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  2. 39cross

    39cross AK Subscriber Subscriber

    Messages:
    937
    Location:
    Beverly, MA
    This doesn't appear to be a tuner issue, you may have better luck in the solid state forum.
    However, I wonder if it's am issue with one of the germanium transistors.
     
  3. andreidaniel

    andreidaniel Member

    Messages:
    55
    With a capacitor in series with a headphones after the colector of TR104 the sound is good. With the headphones connected at the primary of the transformer (at TR105 colector)the sound is distorted with that kind of unusual hiss that appears more or less from time to time. I also verified the voltage between the base and emiter of both TR104 and TR105 and both seems to be 0,19V like most Ge transistors. Should I put something similar like EFT/SFT323 or MP37 Russian transistor instead of Japanese transistor in the place of TR105? The entire device has the ground to ”V+” and is difficult to connect another amplifier, and also the tape won't work when recording from tuner.
     
  4. maxhifi

    maxhifi AK Subscriber Subscriber

    Messages:
    3,094
    Location:
    Edmonton Alberta Canada
    Sounds me like there's a bad component in the amplifier. Check all the transistors with a multimeter for shorts and junction voltage, make sure the capacitors are good, and measure the resistors. Check all the soldering for dry joints and cracks.

    If you lack the skills to troubleshoot and repair this, another option is just to tack in a one chip amplifier IC between the collector of TR104 and the speaker.
     
  5. andreidaniel

    andreidaniel Member

    Messages:
    55
    Here is presented a general problem usually with the driver transistor which works on A class: The guy has a similar problem like mine. After replacement in this video, the hiss disappears.
     
  6. andreidaniel

    andreidaniel Member

    Messages:
    55
    I removed 2SB56 driver transistor and after that all the noise disappeared. When trying to connect C120 from the 1st audio transistor to the input of the audio transformer, there was no hiss. I checked with an multimeter 2SB56 Ge transistor and it seems to be ok. Instead of 2SB56 Ge transistor I tried a configuration with a P-channel FET transistor: 2N5640 and it worked almost perfectly, without (more or less) any adjustment. This is the modified diagram compared to the original. The quality is perfect, no harmonics, no distorsion. The only difference should be a little bit less amplification, and when moving the volume, the physiological point via C116 (300pF) is moved a little bit away. I think that instead of Ge transistor (for the moment) could be used this type of FET which is deplation (always on).

    [​IMG]
     

     

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