blown filtercapacitor in 100watt. Why?

[solidstate2199]

Hi Folks.

i bought a 1988 Laney AOR which works fine. Nice Amp.

One thing which caught my interest is that one of the 6 filtercaps
has been changed sometime ago.

As i open all my new amps to check the overall condition i discovered that
this capacitor must have really blown wide open because there were lots of
residue in the headshell directly under that spot.

What causes this? All other 5 L.C.R. caps looking fine without any dimples on top due
to age.

Im curious to what causes such an event. I guess too much voltage? (caps are 50uf/50uf 500vdc)

Thanks for your insights.

[Enzo]

Probably not overvoltage.   PArts can fail, there is not always a direct cause you can determine.  There could have been a small defect in the part originally that just now finally gave way. 

[tonyharker]

I expect the electrolyte just dried out, which can happen after a few years.  The ESR goes high it gets hot then BANG!  Checking the ESR of a capacitor is a good test of its health.

[solidstate2199]

Thanks for your answers,

it probably wasnt just up to the task or maybe age.

This amp has an obnoxious "bass boost" at low volumes.
For anybody interestet in the AOR Amps here is my very simple solution for this,
it works wonderfully, no need for mods...

I simply take my trusty Alesis Microverb rack unit in the Effects loop, that way you can turn the
Master Volume on the AOR higher and take the volume down on the Effects-Unit Out.

The Louder you turn your Master the more useful the Bass-Boost gets...without the rack Unit
the bass is way too much with the boost pulled, and without it it lacks...

use a rack unit and all good...or play that thing as loud as it gets, i do that anyways.

plus, i dont understand what the fuss is about the effects loop being not useful, it work fantastic
with a line level rack unit..maybe if you try to use pedal which want to see instruments levels...could be.

I havent checked the bias yet..i probably come back to this thread anyways..

Thanks

[phatt]

Remember Electrolytic Caps will die much faster if they are subjected to excess HEAT.
You see this a lot in circuits where some clown mounts a hot running Ceramic Resistor right next door to a big Filter Cap.. And yes even in some of the big brand name gear
Phil.