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    Filament Feeding PAS

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    Pillo69

    Posts : 105
    Join date : 2012-04-11
    Location : Granada (España)

    Filament Feeding PAS

    Post by Pillo69 on Mon Apr 28, 2014 12:14 pm

    I thought of a second transformer to power the filaments in PAS.
    All changes have been kept two diodes (1N4007).
    The placement of a bridge rectifier (4 x 1N4007) is a good choice?.
    Problem with deleting the mass of filaments in PC6?.
    Pictured, top original scheme, bottom diagram with 4 x 1N4007.


    MontanaWay

    Posts : 781
    Join date : 2014-02-06
    Age : 58
    Location : Brookings, Oregon

    Re: Filament Feeding PAS

    Post by MontanaWay on Mon Apr 28, 2014 12:34 pm

    I don't think you need to or should tie the filament down to ground?
    Also, such large cap values too are not really necessary?
    Just my thoughts

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Filament Feeding PAS

    Post by peterh on Mon Apr 28, 2014 2:57 pm

    Doubling 10V will give 24V (not 12 )
    If one can choose transformer i'd rather use a 18V ( or 24V ) and a fullwave bridge.
    The 24V version will also allow the use of a 7812 stab for even better DC


    Pillo69

    Posts : 105
    Join date : 2012-04-11
    Location : Granada (España)

    Re: Filament Feeding PAS

    Post by Pillo69 on Mon Apr 28, 2014 5:32 pm

    I have a transformer 12 +12 v.
    I think use as photography, for future use in the plate tube4hifi tone controls.
    After rectification, transformer 24v. has a voltage of 32v.
    7812 has a 25v input.
    Another stab to 15v. input, you can use 7812?.
    Another better solution?.


    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Filament Feeding PAS

    Post by peterh on Tue Apr 29, 2014 1:41 am

    The 7812 has 12V output, that's correct. But With a pair of suitable resistors it may deliver +24V ( see the datasheet at http://www.fairchildsemi.com/ds/LM/LM7812.pdf )
    Note that there exists a 7824 that should fit fine as long as you can get hold of it, If not see page
    19 of the above datasheet "howto set any output voltage".

    The 78xx must have a cooling mount, that could be a heatsink or an chassies that transports heat. PAS-chassie does not!

    As for your drawing, i'd connect the 2 12V outputs in series, creating 24V AC, then rectify with a bridge rectifier, capacitor a 78xx , another cap and then feed that PAS boards with 24V as in the original) Less currecnt means less hum ( yes there will be some hum remnants even after the 78xx)

    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: Filament Feeding PAS

    Post by tubes4hifi on Tue Apr 29, 2014 7:47 pm

    super easier way to add a power transformer . . . . leave the existing power transformer to power all the existing tube filaments
    EXCEPT that the new transformer will ONLY power the 12X4 tube (it needs 12vac @ 300ma).   Don't forget to replace the pilot lamp with an LED,
    that will save you another 150ma.
    So originally the transformer needed to supply 750ma of current, now the old one will only need to supply 300ma plus 5-10ma for the LED !!!
    This way you don't have to worry about converting anything else to DC.
    BTW, the original PAS transformer puts out about 10.5vac (it's too gutless to put out 12vac with all the load on it) and you wind up with about 22-23vdc
    to run the filaments in series connection. Once you relieve it of working so hard by powering the 12X4 separately with 12vac,
    you'll wind up with about 24-25vdc which is perfect.

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Filament Feeding PAS

    Post by peterh on Wed Apr 30, 2014 2:02 am

    tubes4hifi wrote:super easier way to add a power transformer . . . . leave the existing power transformer to power all the existing tube filaments
    EXCEPT that the new transformer will ONLY power the 12X4 tube (it needs 12vac @ 300ma).   Don't forget to replace the pilot lamp with an LED,
    that will save you another 150ma.
    So originally the transformer needed to supply 750ma of current, now the old one will only need to supply 300ma plus 5-10ma for the LED !!!
    This way you don't have to worry about converting anything else to DC.
    BTW, the original PAS transformer puts out about 10.5vac (it's too gutless to put out 12vac with all the load on it) and you wind up with about 22-23vdc
    to run the filaments in series connection.   Once you relieve it of working so hard by powering the 12X4 separately with 12vac,
    you'll wind up with about 24-25vdc which is perfect.
    Speaking about easy : replacing the 12x4 with 2 diodes is even easier, and neeeds no extra transformer.

    Tiziano73

    Posts : 29
    Join date : 2012-09-11
    Location : Italy

    Re: Filament Feeding PAS

    Post by Tiziano73 on Wed Apr 30, 2014 6:20 am

    Hi,
    as suggest by Tube4hifi you can use original power transformer to drive only pilot lamp and 12x4 tube and use a new power transformer to drive the 4 12AX7.
    After the the original voltage multiplier are there about 23Vdc.
    For better results you can power the four 12AX7 instead the original voltage multiplier using a new power transformer with one output 24Vac. It must drive an a.c. to d.c. converter that use LM338T. Transformer and converter are to able to supply until 1A for an intensive use. In this way you can fine adjust 12ax7 heater supply until the 11Vdc showed in Dynaco PAS Manual and you will improve all PAS specs.
    I use a Block PCB transformer with low irradiated magnetic field but i suggest, for best results, to put between the new power transformer and the PC-5 board a little screen to make little Faraday cage (you can cut and use a PC power supply cage and fix it with the PC-5 screws board.

    Hope this help.

    BR

    Tiziano

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