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    Budget replacement caps, ST 70

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    scsidude2

    Posts : 21
    Join date : 2010-03-19
    Age : 29
    Location : Dekalb, IL

    Budget replacement caps, ST 70

    Post by scsidude2 on Thu Apr 08, 2010 9:21 pm

    Found these 100uF+100uF / 500VDC Caps, was wondering if anyone had an ideas about how well they might work in replacing my old quad caps. Thanks!
    http://angela.com/100uf100uf500vdcclampmountelectrolyticcapacitor.aspx

    GP49

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

    Re: Budget replacement caps, ST 70

    Post by GP49 on Fri Apr 09, 2010 12:56 am

    Electrically...as long as their SURGE voltage is 525 volts or more....they represent an upgrade to what originally came in the Stereo 70 (and it does benefit from more power supply storage) but you may encounter some difficulty in getting them to fit in the space available to you.

    At their size, you may be able to squeeze them in underneath the chassis.

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Budget replacement caps, ST 70

    Post by Bob Latino on Fri Apr 09, 2010 6:35 pm

    scsidude2 wrote:Found these 100uF+100uF / 500VDC Caps, was wondering if anyone had an ideas about how well they might work in replacing my old quad caps. Thanks!
    http://angela.com/100uf100uf500vdcclampmountelectrolyticcapacitor.aspx

    The voltage rating of 500 VDC would probably be OK on the ST-70 which does have a working high voltage of 430-440 VDC but does surge higher at turn-on. The general consensus is that the first section of the quad cap should be no more than 40 or 50 uF. Anything higher places a strain on the rectifier tube. This cap is also made in a 50 uF + 50 uF version. Probably two caps - One of the double 50 and one double 100 would work OK. One could be put in the quad cap slot and as GP49 has mentioned you would have to squeeze in the other cap (probably under the left output transformer) somewhere.

    IMHO, rather than go through the bother of where to place the caps and then stringing wire, the choke and resistors between the 4 sections of the two caps, you should probably just bite the bullet and spend the extra $33 and get the Dynakitparts 550 volt quad cap.

    If you did use one 50, 50 uF and one 100, 100 uF cap on a stock ST-70 you should probably wire them up like this > pin 8 of the rectifier tube > 50 uF > choke > 100 uF > 6800 ohm resistor > 100 uF > 22,000 ohm resistor > 50 uF. It will work but consider the fact that if you ever sell the amp you will probably devalue the amp in the eyes of a prospective buyer by having a non standard DC B+ power storage system for your amp.

    Bob

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