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    Recommend replacement 2000uf rectifier caps for PAS

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    Dry Rub

    Posts : 1
    Join date : 2011-02-07

    Recommend replacement 2000uf rectifier caps for PAS

    Post by Dry Rub on Sat Jan 07, 2017 1:43 pm

    I'd like to replace the selenium rectifier with diodes and replace the larger caps below it while I'm at it. While it's been easy to find info on the diode type to use, I've found so many different comments about what caps and values to use when replacing the two large 2000 uf caps. I'm not interested in a replacement board, just need someone's advice for appropriate replacements. Seems like an increase in uf value is often suggested but I don't want to choose the wrong thing when it comes to the uf or voltage values.

    Links to caps would help too! Thanks.

    peterh

    Posts : 718
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Recommend replacement 2000uf rectifier caps for PAS

    Post by peterh on Sat Jan 07, 2017 2:00 pm

    Dry Rub wrote:I'd like to replace the selenium rectifier with diodes and replace the larger caps below it while I'm at it. While it's been easy to find info on the diode type to use, I've found so many different comments about what caps and values to use when replacing the two large 2000 uf caps. I'm not interested in a replacement board, just need someone's advice for appropriate replacements. Seems like an increase in uf value is often suggested but I don't want to choose the wrong thing when it comes to the uf or voltage values.

    Links to caps would help too! Thanks.
    You install then either as the original ( needs to fit in the clamps ) or
    much better on one board ( an example below) http://n.manet.nu/tubedoc/PAS_PS-V3.0-Install.pdf

    PeterCapo

    Posts : 400
    Join date : 2008-12-05

    Re: Recommend replacement 2000uf rectifier caps for PAS

    Post by PeterCapo on Sat Jan 07, 2017 2:44 pm

    There are several individual parts to choose from.  Originally, the voltage rating for the electrolytics was sufficient in the vicinity of around 16VDC.  But, nowadays I suppose I wouldn't go less than around a 20VDC rating, each.  I'd suggest the following, though you can choose electrolytics with more capacitance: 

    Filament supply electrolytics: Two at $3.45 each, Mouser Part #: 598-338TTA035M http://www.mouser.com/ProductDetail/Cornell-Dubilier/338TTA035M/?qs=%2fha2pyFadugk%252bEg6r3tts1YGzrxizHcf6pv5l72erOVaScxbFSdnLg%3d%3d

    Filament supply diodes: Two at $0.35 each, Mouser Part #: 833-UF4007-TP http://www.mouser.com/ProductDetail/Micro-Commercial-Components-MCC/UF4007-TP/?qs=%2fha2pyFaduipzxuFFZQBdwE9%2fS0ZbofHh6Ba5FPG54cyxV4uqqQi1Q%3d%3d

    Terminal strip for mounting the new diodes, one at $0.78: Mouser Part # 534-818 http://www.mouser.com/ProductDetail/Keystone-Electronics/818/?qs=sGAEpiMZZMsQtlBhqKq43VFZIBrnnwN5

    This is a 1:1 parts replacement in the same location as the original parts.  Suggest sleeving on the leads of the electrolytic capacitors.  You might have to increase the diameter of the mounting hole on the terminal strip.  Check filament voltage when work is done, as present-day diodes may have a lower voltage drop than the original selenium rectifier.  If the filaments run too high after the new diodes are installed, it might be necessary to add a resistor or two to bring them back down.  In fact, it would be a really good idea to check the voltage at all of the test points given in the original PAS manual.  It's on the right side of the page with the schematic for PC5 and the power supply.


    Last edited by PeterCapo on Sat Jan 07, 2017 9:19 pm; edited 1 time in total (Reason for editing : Voltage rating.)

    j beede

    Posts : 339
    Join date : 2011-02-07
    Location : California

    Re: Recommend replacement 2000uf rectifier caps for PAS

    Post by j beede on Sat Jan 07, 2017 4:40 pm

    Here's the B+ and filament supplies on a single small board that fits where the selenium stack was. I get my caps from Antique Electronic Supply. The diodes from Fry's or Radio Shack.

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