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    Separate filament transformers

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    Dahlberg

    Posts : 102
    Join date : 2016-09-27
    Age : 56
    Location : Sweden

    Separate filament transformers

    Post by Dahlberg on Wed Jan 18, 2017 9:07 am

    I get a bit more hum/noise after the amps have been on for a couple of hours
    and the power transformer has reached it's maximum temperature. Now I'm
    speculating about separate transformers for filament as a way to reduce the
    consumption from the main power transformer. I have found a 50va toroid
    that's 80x35mm and I belive that I would be able to fit two of these in each
    M-125 amp. They do not have any centertap but I found this description for
    a workaround. Any comments ?

    http://www.augustica.com/Tutorials/Tubes/mains_filament_wiring.htm
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    Captain Coconut

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    Join date : 2009-10-13
    Age : 64
    Location : Great White North

    Re: Separate filament transformers

    Post by Captain Coconut on Wed Jan 18, 2017 11:47 am

    Not a bad idea, if you have the room. It will make the PT run cooler. You can heat up the tubes prior to powering up the PT providing you put the filament transformers on a separate switch.

    nmchiefsfan

    Posts : 36
    Join date : 2012-03-21

    Re: Separate filament transformers

    Post by nmchiefsfan on Wed Jan 18, 2017 1:31 pm

    And have the power for the PT gated through the power switch for the FT so you can't put anything on the plates until the FT is switched on.
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    Dahlberg

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    Join date : 2016-09-27
    Age : 56
    Location : Sweden

    Re: Separate filament transformers

    Post by Dahlberg on Wed Jan 18, 2017 8:19 pm

    Transformers and steel covers (90x38mm) are ordered.
    The plan is to mount the transformers on the bottom, outside of the amps.

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    Peter W.

    Posts : 348
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Separate filament transformers

    Post by Peter W. on Wed Jan 25, 2017 8:44 am

    I would like to know if the hum/noise is mechanical (external) or through the speakers (internal)?

    Your post is not clear on this. If external, your solution should do nicely. It remains to be seen if internal. Even if temperature-related, there are so many potential contributors as to single out the power-amplifier may not be the actual solution.
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    Dahlberg

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    Re: Separate filament transformers

    Post by Dahlberg on Wed Jan 25, 2017 8:59 am

    It's internal.
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    Peter W.

    Posts : 348
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Separate filament transformers

    Post by Peter W. on Wed Jan 25, 2017 9:17 am

    OK.

    a) The filament transformers cannot hurt, will reduce the load on the PT, and may help. That they are shielded is a very good thing.
    b) IF this does not work, look after the main filter caps. Heat is the constant enemy of capacitors, and they are also wearing parts, if only over a very long time. But as you describe the symptoms - coming on after everything reaches full operating temperature - as capacitors age, their internal resistance increases which, in turn makes them get hotter, which increase internal resistance.... you get the picture.

    At the same time, adding filament transformers will remove heat to the outside of the chassis, and may even address this possibility.
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    j beede

    Posts : 382
    Join date : 2011-02-07
    Location : California

    Re: Separate filament transformers

    Post by j beede on Wed Jan 25, 2017 12:13 pm

    You asked for comments:

    I would have run an experiment using a simple (cheap) separate filament transformer before ordering anything. If that experiment worked, I might have tried isolating one filament at a time to locate the root cause.

    You could provide dc to the filaments using an external supply as an experiment. This could confirm or eliminate the filaments as the source of your noise.

    Have you run the amps with the "forward" output tubes removed? Then with the "rear" tubes removed? If there is a proximity issue this may show it.


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    Dahlberg

    Posts : 102
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    Age : 56
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    Re: Separate filament transformers

    Post by Dahlberg on Wed Jan 25, 2017 2:49 pm

    It's quite obvious that it's heat related. The room where I listen to music gets ~8°C
    warmer in the summer so I thougth I will fix this before then. The tube filament
    draws close to 10A so a regulated supply isn't that easy to find. I have some two
    channel 1083 supplys that's possible to run in parallel but 10 amps is a lot so I
    dropped that idea. That would have to be an external solution as well and I didn't like that.

    I'm going to be more thorough when locating the filament wiring this time and hopefully the
    amps will be dead silent after this little side project is done.
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    peterh

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    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Separate filament transformers

    Post by peterh on Wed Jan 25, 2017 3:51 pm

    If you take the time to convert to 12V then a switchmode powersupply would fit fine.
    The ecc82/12AU7 can use 12 by rearranging the filaments ( need to cut traces on the board sorry),
    the powertubes might be connected in series a simple wiring would do.

    Perhaps powering the powertubes would be all needed ? Thats a few minutes of work to arrange.
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    Dahlberg

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    Age : 56
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    Re: Separate filament transformers

    Post by Dahlberg on Wed Jan 25, 2017 4:26 pm

    Transformers are already at the DHL pick up spot Cool

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