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Palomar 300a Transformer hum

Discussion in 'Amplifiers' started by Jimbo165, Jul 22, 2016.

  1. Jimbo165

    Jimbo165 Active Member

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    I picked up a Palomar 300a not working it is a amp with transformer in separate box. I replaced Keying transistors and amp was working but on just key up in power operate mode transformer has a hum. I replaced all capacitors and power rectifier diodes but on key up in power operate mode still has hum. It has no hum when just power on . I have used amp over 6 hrs so far and it works like it should on output and transformer does not get hot or smoked yet. Is transformer going bad or is this normal for this amplifier? Thank You Jimbo


     

  2. Beetle

    Beetle Sr. Member

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    Try tightening all the bolts/nuts that hold the laminations together.
     
    wavrider likes this.
  3. Jimbo165

    Jimbo165 Active Member

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    Beetle I tightened up 4 bolts holding laminations also did not make a difference. When I run amp on low less hum than with amp on hi. Thanks Jimbo
     
  4. midnight special

    midnight special Well-Known Member

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    i dont know if this will help here or not but years ago a tech i knew had a old 6 channel cb that had a transformer humming and he put super glue in the transformer and it went away,, dont ask me the how and what but that is what he said he did,,,,,,,,
     
  5. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    What you are hearing is called Magnostriction.(SP?) When the ac is doing it's thing it is pulling on the metal in the core. Enamel is what the manufacturers used. Might not be much you can do except change the transformer.
     
  6. vkrules

    vkrules Sr. Member

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    Real common in old transformers. Make sure everthing is tight and can't vibrate in the case. Then if still present try enamel or super glue etc on the lamination's. Works wonders ! I have fixed several transformers like this over the years.
     
  7. WMS

    WMS BANNED

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    Manufacturers used Shellac, not Enamel... Use a Search Box for Transformer Potting, or you can read it here from one of my favorite Amplifier Technicians
    http://www.somis.org/D-amplifiers3.html
    Potting has multiple advantages, especially for these Vintage Transformers, if you read the Article...
     
    vkrules and Tallman like this.
  8. Beetle

    Beetle Sr. Member

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    The vibrating might be getting transferred to the chassis and making it vibrate also. If you can remove the bolts that secure the transformer to the chassis you could put a soft rubber pad or something similar down directly on the chassis underneath the transformer. You might also be able to put rubber snubbers, grommets or whatever around the bolts.

    This MIGHT quiet it down a bit, but not completely.
     
  9. vkrules

    vkrules Sr. Member

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    Yes I know but shellac is getting hard to find.
     
  10. WMS

    WMS BANNED

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    I'm surprised to read that ! You are much closer to the source than I am here in the U.S.A.... NO shortage of it here...
    I would think you can get it in the "Natural" form shipped to you and then dissolve the Dried Flakes in Denatured Alcohol or Ethanol...
    https://en.wikipedia.org/wiki/Shellac
     
  11. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    They use polyester resin for fiber glass these days. Before that it was enamel for the heat resistant properties. Laquer and Shellac both fell out of favor because of all of the V.O.C.s and the air pollution problems. Vaporizing alcohol has a tendency to go BOOM!
    http://www.somis.org/D-amplifiers3.html
    Polyester fiberglass laminating resin
     
    #11 Tallman, Jul 24, 2016
    Last edited: Jul 24, 2016
  12. vkrules

    vkrules Sr. Member

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    Epoxy works , thin it down with a bit of alcohol and paint it on. Most cases it's the lamination's buzzing and you wont have to pot the winding.
    Womens clear nail polish works as well ,dries hard but still a little flexible.( no honey I haven't seen your nail polish)
     
  13. WMS

    WMS BANNED

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    I already provided that Link above to Richard Measures' Website...
    Shellac was used for years by General Electric that used to be Partners with Westinghouse... THEY pretty much were responsible for the Electric Grid...
    Enamel also has a Thinner and can go BOOM !!! Once the Thinner evaporates, there is no more chance of BOOM...
     
  14. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Without the assistance of Nikola Tesla THEY would have done nothing.
     
    Captain Kilowatt likes this.
  15. nomadradio

    nomadradio Analog Retentive

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    A bad rectifier can cause a transformer to "grunt", and make noises under load.

    As a rule, if this is the cause, it will get louder when you're keyed and drawing current from the transformer's HV winding.

    And if it's just loose laminations, it will hum all the time.

    73
     

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