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HME HM 150 Bi Linear Amplifier Question

Discussion in 'Amplifiers' started by JB383RI, Jul 25, 2021.

  1. JB383RI

    JB383RI New Member

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    Hello everyone I've been reading the forums on here for a long time and finally decided to make a account and start posting. This is a great site and I look forward to being part of the community.

    I just recently got this HME HM 150 Bi Linear and it didn't work. I re-caped it and changed all the carbon composition resistors to modern metal film ones and now it works great.

    So because it's a BI Linear the Pre-Amp is always on and there's no switch to turn it off. It doesn't really work that good plus I don't want it on full time.



    Is there a way to disable it internally?

    Please let me know if you need more info on the Amp or need pictures. Thanks a lot.
     

  2. nomadradio

    nomadradio Analog Retentive

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    I have seen people asking for a diagram for HME amplifiers on the web, and the net pre-web for decades.

    A Google search has always turned up only requests, no sources.

    There is bound to be a way to bypass a preamp. But the nitty-gritties of where things connect dictates how to go about it.

    And if someone wants to step up and volunteer to reverse-engineer this kind of info, he (she?) would still need a working sample of that model to trace down and draw up a proper schematic.

    Reminds me of a Monty Python sketch. A line of soldiers at attention are asked to volunteer for a dangerous assignment. All of them but one take a step backwards, leaving the one soldier out front of the line.

    I just took one step back.

    73
     
    NZ8N likes this.
  3. JB383RI

    JB383RI New Member

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    Maybe some pictures will help. Come on guys any ideas?


    09EF726E-729C-4928-BE93-BD4253F39D74.jpeg A17FDB57-59C9-4EA3-8A41-329A754C1DCA.jpeg 7F35FA59-909E-4B65-805F-6CB7DA16E5A7.jpeg AE4E7874-8734-4FBA-9C2A-A97A60C681CC.jpeg FED67C61-2591-4BF6-ABB2-B92EA3C98AAA.jpeg B84CC301-E499-4ED2-A5E7-5125662DD8E3.jpeg 681C575F-71BB-4C58-ACB9-F351A9A5D676.jpeg 92385BDB-8EF5-40C6-8450-83F13738EEAC.jpeg 270B119B-37F4-42F5-AA94-E07FB719825D.jpeg F371889E-E208-4AF4-BDCF-59AE2C4F0A0E.jpeg
     
  4. Wire Weasel

    Wire Weasel Senior Moment

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    Hmmm. Well it says "bi-linear" but I have never seen such an amp that had a full time RX Premplifier that wasn't accompanied by a factory switch to operate it. You say it doesn't seem to work .... how do you know for a fact that it has one at all or that it's working at all if it even has one. Do the RX signals (plus sound) on your radio's meter increase when you turn the amp on? If they do .... then it apparently does have a RX Preamp. - And again you say it doesn't work well. Please explain what you mean by that exactly.
     
  5. nomadradio

    nomadradio Analog Retentive

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    The preamp has a relay, but no switch.

    An odd one. Has to have the preamp relay so you can leave it in line turned off.

    I see two possibilities: Cut the trace feeding power to the preamp relay's coil. This only works if the relay's standby-side contacts are working properly.

    -Or.. Just remove the preamp relay, and put a wire jumper across the center two of the six contact foil pads. If it turns out the relay's standby side also has problems, this gets around those.

    73
     
    NZ8N, JB383RI and 144inBama like this.
  6. JB383RI

    JB383RI New Member

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    So I found the 12 volt supply to the pre-amp relay and desoldered the pin and it works great. No more full time pre-amp. Thanks again nomdradio I appreciate it.
     
    NZ8N likes this.
  7. nomadradio

    nomadradio Analog Retentive

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    Gotta love it when a plan comes together. Congratulations! problem solved.

    73
     
    BJ radionut likes this.

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