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Old 28th November 2008, 02:01 PM   #1
ids987 is offline ids987  United Kingdom
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Join Date: Nov 2008
Default Cap's needed C-Audio ST 600

Hi There,

I'm a newbie on this forum, although I have done a lot of "DIY audio" in the past. Mostly amps, pre-amps, and speakers. Since marriage, and children came along, I haven't really been active in this, although a couple of my old projects are still in my home system - including a pair of the old Wilmslow VOLT / MacDonald transmission line speakers - still in original MDF.

Anyway, enough about me !
A friend has asked me to look at an oldish C-Audio ST 600 amp. After some poking around, I suspected faulty reservoir cap's on one channel. It seemed weird, because both the caps's on the left channel seemed dead. When I removed them, I found that one leg had broken on each cap - that could explain it !
Just wondering if anyone here may know where I could locate some suitable cap's. The originals are non-standard - 4,700uF / 110V. The DC rails on the good channel measure about +/- 105V. I can get either 4,700uF / 100V, or 4,700uF 120V. I don't really want to risk 100V cap's (especially as it's not my amp), and the 120V cap's are about 5mm bigger (diameter) - which won't go in without some mod's. The original cap's were Aerovox. After some googling, I found that Aerovox either were, or became BHC Aerovox, but they don't make these any more. I suspect they were probably "specials".

Many Thanks for any info received:
Ian
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Old 29th November 2008, 05:21 AM   #2
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HaflerFreak's Avatar
 
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Location: Westmont, IL
Default Info....

Hi Ian, welcome,

I don't know much, but I know caps.
Warning, I have little more than a technicians grasp on this stuff, so take what I say with a grain of salt.

First, If I were a member on this forum (with much more knowledge) looking at your post, I would want to know a few things:
1. The description of the original problem or complaint from the amps owner.
2. Did you measure AC ripple, etc., what do you mean by 'dead caps'?
3. Is there any other collateral damage from the 'dead caps'.
4. Precise dimensions of capacitors in mm or inches, preferably both.
5. Screw terminal, snap-in or through hole leads????

A few other things I would ask are:
How did you remove the caps, are you sure that you did not cause the 'broken leg' when you removed them?

Are you constrained to a circuit board or bracket layout.

Send us a picture man!!!
------------------
found these at mouser.com
CGS572U150X4C
Mallory Screw Terminal, Computer Grade Electrolytic Capacitors 5700uF 150V-10+75% Data Sheet In Stock
1: $41.94
10: $37.28
25: $33.55
50: $29.82
100: View
Min.: 1
Mult.: 1
Details 5700 uF 150 Volts 37 mOhms 3 in Dia. x 4.125 in L

CGS672U150U4C
Mallory Screw Terminal, Computer Grade Electrolytic Capacitors 6700uF 150V-10+75% Data Sheet In Stock
1: $41.94
10: $37.28
25: $33.55
50: $29.82
100: View
Min.: 1
Mult.: 1
Details 6700 uF 150 Volts 22 mOhms 2 in Dia. x 4.125 in L

CGS532U150U4C
Mallory Screw Terminal, Computer Grade Electrolytic Capacitors 5300uF 150V-10+75% Data Sheet In Stock
1: $36.99
10: $32.88
25: $29.59
50: $26.30
100: View
Min.: 1
Mult.: 1
Details 5300 uF 150 Volts 23 mOhms 1.75 in Dia. x 4.125 in L

CG562U150X3L
Mallory Screw Terminal, Computer Grade Electrolytic Capacitors 150V 5600uF In Stock
1: $47.09
10: $41.85
25: $37.67
50: $33.48
100: View
Min.: 1
Mult.: 1
Details 5600 uF 150 Volts 14 mOhms 3 in Dia. x 3.625 in L
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Old 29th November 2008, 07:07 PM   #3
ids987 is offline ids987  United Kingdom
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Join Date: Nov 2008
Hi HaflerFreak,

Thanks for the welcome, and the reply.
The owner of the amp complained of distortion - with hum over the top of louder notes. When I measured voltages, the right channel measured +/- 105V, the left measured +/- 69V. The diodes in the bridge all tested ok, and the two transformer secondaries (one per channel) were symmetrical at about 78-0-78V. When I removed mains power, both rails on the left channel fell off a cliff. The rails on the right channel faded away gracefully. The cap's on the left channel also felt loose. I desoldered them carefully and they fell out. I am sure I didn't break the legs.
The cap's are snap in types, 35mm diameter, 50mm long. Ideally I want cap's which will physically fit the board. The 4,700uF 120V cap's I found are 5mm bigger, and will not fit without mod's.
If I can't get the same, there is probably enough left of the broken legs to solder in. Not enough to go through the board, but it is a good quality double sided board, and the cap connections are through plated. Part of me thinks it may have been that way from new, as I couldn't find the bits which broke off. If the worst comes to the worst, I can glue the cap's as well. I could mount bigger cap's elsewhere, but it would compromise the grounding.
Sorry, typing fast as I'm on the way out....

Thanks Again:
Ian
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