[sdiy] Power supply caps

[Seb Francis]

Just out of interest I did a quick search for 8200uF 80V capacitors and 
found this one at £3.28
Size is 35mm wide by 45mm high (so that's like 1.5" x 2" using your 
funny old fashioned measurements)

http://uk.farnell.com/jsp/Passive+Components/Capacitors/UNITED+CHEMI-CON/ESMH800VNN822MA45T/displayProduct.jsp?sku=1360697

Says it's stocked by Newark which is the right side of the pond for you.

Seb


David Cornutt wrote:
> Not strictly a synth problem, but it has to do with my monitor amp...
>
> The TEAC receiver that I use as a monitor amp developed a nasty 60 Hz 
> buzz.
> It was audible in both the speakers and the headphone output, and it was
> insensitive to the volume knob or the other controls, so I figured it 
> had to
> be in the output supply.  Interestingly, this amp has a piece-built 
> supply,
> with discrete diodes instead of a packaged rectifier.  I scoped both 
> sides
> of the output supply and saw that the positive side had a ripple.
>
> Unsoldered the diodes from that side, and they checked out OK
> (using an old analog meter).  I then unsoldered both of the filter caps.
> On my digital hand-held, which only measures up to 20 nF capacitance,
> one of the caps read infinite, which I expected.  (I put the meter on a
> resistance setting, and I could see the resistance going up as the
> meter charged the cap.)  But the other one only measured about
> 700 pF capacitance, and on the resistance measurement it read
> at around 2K ohms, and I did not observe any charging behavior.
> The suspect one also has visible bulging at the ends, so that pretty
> much confirms it.
>
> Now the problem.  I don't know where these caps came from and
> I can't find a replacement.  They are marked with the brand name
> "devcon".  They are marked as 8200 uF and 105C, 80V.  Physically,
> they are about 3" tall and 1" high.  That made me wonder since
> it seems like an awful lot of farad to cram into a package this small,
> but hey, I'm vaguely aware that there have been advances in
> large-value caps in the last few years.  I don't usually mess with
> caps this big, so what do I know?
>
> Well, I got out the Mouser catalog and started searching.  According
> to my scope, the (unregulated) supply runs at about 60V, so I
> figured maybe it would be better if I replaced these with 100V
> types (I'm going to replace both of them while I'm at it).
> Problem: I've only found two 100V caps at near that value in
> the catalog, a Mallory part and a Vishay-Sprague part.  And
> they are both larger than the part that they are replacing, plus
> they have screw terminals which means they can't be soldered
> directly into the board the way the old ones were.  Finding space
> inside the enclosure to mount them is going to be a problem.
> Plus, the darn things run about $25 a pop.
>
> So the questions are: (1) Has anyone ever heard of this "devcon"
> company?  The only thing Google turns up is a company that
> makes epoxies.  (2) Could these things really be 8200 uF in
> that size package?  Or did TEAC get shafted by some counterfeit
> parts?  (3) Does an 80W/channel stereo amp really need caps
> that large?  Looking in the Mouser catalog, I can get some
> snap-in types (which would solder right in where the old ones were)
> at around 2200 uF, 100V, and spec'ed for high ripple current,
> for less than half of what the higher-value ones cost.
>
>
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