Shimizu SS-105S: 1.5 Amps in RX?

Discussion in 'Radio Circuits, Repair & Performance' started by IZ2EWV, Jul 27, 2019.

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  1. IZ2EWV

    IZ2EWV Ham Member QRZ Page

    Hello dear friends,
    This post of mine is addressed to the owners of this radio.
    I recently added to my "collection" of vintage radios a fine Shimizu SS-105S (10 W Pout version). At the moment, I tried it in RX, and the listening is very good, as well as the impression of sensitivity.
    But, after half an hour, I was disconnecting it from the cables and I found the rear of the radio warm, like I used it in TX. Then, I measured the supply current, and it it was 1.5 A during RX...
    It seems something high, but unfortunately the operation manual declares only the current in TX.
    I ask you if any owner of the SS-105S could give me some reference or experience, to help me investigate.
    I didn't open the equipment yet (obviously I'm not the first owner) and I don't know the previous history of my radio. I guess that it maybe a matter of bias of the PA stage, but looking at the schematic diagram, no trimmer pot is provided inside for that scope.
    Tnx in advance.
    73 de Alberto, IZ2EWV
  2. G4COE

    G4COE Ham Member QRZ Page

    See if this link will help Shimizu SS-105S. I'm wondering if the TX bias is stuck 'ON' this is just a wild, wild guess, may be if you feel around what is getting 'hot', i.e. PA, regulator or maybe the audio amplifier, leaky speaker dc isolation capacitors for example.

  3. IZ2EWV

    IZ2EWV Ham Member QRZ Page

    Tnx Dave,
    I just visited Martyn's page and sent an e-mail to him, but unfortunately withous answer (maybe he changed address?).
    I was wondering the same: I measured voltage of about 0.8 V at the "TB" rail, which should activate the tx supply in several circuits, included the low current control of the PA. I will check if it is normal by looking at the schematic diagram...
    73 de Alberto, IZ2EWV
  4. G4COE

    G4COE Ham Member QRZ Page

    If I come across anything I'll get back here, in the meantime good luck.


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