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    Pas-2 multi section capacitor and transformer replacement

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    maninmac771

    Posts : 30
    Join date : 2011-03-07

    Pas-2 multi section capacitor and transformer replacement

    Post by maninmac771 on Fri Mar 27, 2015 8:16 pm

    I'm thinking of firstly replacing the aged multi-section capacitor of my PAS-2.  I came across a NOS Dyna quad cap in eBay with same rating as the stock one, i.e. 30/20/20/10 @450VDC, and another from dynakitparts.com - 20/20/20/20 @475 VDC.  Would it be better to replace with the one from dynakitparts, which has seemingly lower uF ratings (20/20/20/20) but higher VDC, instead of the NOS dyna cap with exact ratings as the stock cap?  Secondly, is replacing the PAS-2 transformer with new identical one is the way to go? or is there other alternative transformer that would even do a better job?  Appreciate advices please.  Thanks.

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Pas-2 multi section capacitor and transformer replacement

    Post by tubes4hifi on Fri Mar 27, 2015 10:08 pm

    you always take your chances with stuff from ebay, from DynaKitParts you'll be getting good stuff for sure!
    For the power transformer, the only alternative I know of is the HD power supply upgrade I have available,
    but it's kind of overkill for a stock preamp and 3X the price.

    GP49

    Posts : 718
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Pas-2 multi section capacitor and transformer replacement

    Post by GP49 on Fri Mar 27, 2015 10:49 pm

    The stock transformer is adequate for a stock PAS (or a modified one running four 12AX7).  You might consider doing what Frank Van Alstine does: remounting it on the OUTSIDE of the back panel.  Wiring can easily run through the ventilation slots on the back to a terminal strip inside (it's
    also a good place to put a LINE FUSE that is not present in the stock Dyna PAS).  This will free up some real estate that you can use for additional power supply capacitance if you wish (although modern capacitors for the DC power supply are substantially smaller than Dynaco's originals) and the transformer will run cooler.  Also this puts whatever hum field it generates OUTSIDE the preamp case.

    Measure your filament voltage, too.  If it is low on an old PAS, replace the selenium rectifier for the filament supply with silicon diodes.  Low filament voltage causes flabby, ill-defined sound and long warmup time.

    If it were up to me, I'd get a new part from a known vendor. "NOS" could be fifty years old!

    peterh

    Posts : 642
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Pas-2 multi section capacitor and transformer replacement

    Post by peterh on Sat Mar 28, 2015 3:06 am

    maninmac771 wrote:I'm thinking of firstly replacing the aged multi-section capacitor of my PAS-2.  I came across a NOS Dyna quad cap in eBay with same rating as the stock one, i.e. 30/20/20/10 @450VDC, and another from dynakitparts.com - 20/20/20/20 @475 VDC.  Would it be better to replace with the one from dynakitparts, which has seemingly lower uF ratings (20/20/20/20) but higher VDC, instead of the NOS dyna cap with exact ratings as the stock cap?  Secondly, is replacing the PAS-2 transformer with new identical one is the way to go? or is there other alternative transformer that would even do a better job?  Appreciate advices please.  Thanks.

    The alternative is to get a powersupply board that has caps for both the B+ and the filament. There is at least 2 sources, tubes4hifi has one ( the cheapest one of the alternatives ) and triodeelectronics
    http://triodeelectronics.com/sdslacabofor.html
    The last one has the option of using Si diodes instead of the 12x4, this save additional space.

    As for transformer, you did not say why. If it's broken the only exact replacement i know is
    http://triodeelectronics.com/pa2powtrandy.html
    There is sometimes one circulating on ebay that claims to be replacement for PAS-3/3, it'smade in hongkong,
    DON'T buy it. It has the wrong dimensions, and they seem to fail reliably.
    If you need a larger transformer to get more juice, i know no such thing. The best option seems to be to
    add one at the back of the pas3( and keep the internal at least for filaments)

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Pas-2 multi section capacitor and transformer replacement

    Post by tubes4hifi on Sat Mar 28, 2015 2:27 pm

    DynaKitParts.com has the PA211, I have one, and I also have a used one in known good working condition $20

    maninmac771

    Posts : 30
    Join date : 2011-03-07

    Re: Pas-2 multi section capacitor and transformer replacement

    Post by maninmac771 on Wed Apr 01, 2015 4:26 pm

    Thanks for the advices. I actually have replaced the stock selenium rectifier and its capacitors with a cap board which I just found out also replaces the stock multi section capacitor (which I have not removed from the chassis). So, the need for replacement of the cap is a non-starter. As for the transformer, it"s not broken - because everything is working fine. It's the fact that the transformer is old and it's been said that it's only considered "adaquate" for the job, that I was wondering whether a new transformer with better construction would beef up its function and provide some improvement. For the Van Alstine's way to remount the transformer on the outside of the chassis, could you point me to the right direction(or link on the net) to follow? Thanks.

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Pas-2 multi section capacitor and transformer replacement

    Post by tubes4hifi on Wed Apr 01, 2015 6:07 pm

    if you go to google.com and type in "Van Alstine" it will be the first thing that comes up.
    He wrote some articles on modifying the PAS3 30 years ago, but the specific information is not on his site.
    You could ask if he wants to sell it to you, but how hard is it to remove the transformer and then re-mount it on the back of the chassis?

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