- Jun 16, 2020
- Reaction score
electrolytic filter caps will 'dry out' over time regardless. using them on occasion won't prolong anything.
It's not the drying out that regular usage attempts to prevent. KB0NES said it best here:
Powering up the amp from time to time does nothing to prevent electrolytic capacitors from 'drying out'. But it does help reform the oxide dielectric layer that forms inside an electrolytic cap that degrades over time. An electrolytic capacitor that has sat inactive for years can have the insulating dielectric degrade to the point that when powered on again instantly causes the capacitor to short.
Every capacitor will fail eventually, but you can do certain things to get the 'most joy' out of them. Preventative maintenance is just something hardly anybody will ever follow through on. So be it.
my experience is that filter caps last far longer than people on the web, tube amp gurus, profess. i have caps in one amp in place for 15 years and there's no sign of any problems.
Of course, they don't have a built-in expiry timer. Still do you want to trust an old electrolytic after a couple of decades, for example? Would you put 20 year old petrol in a car?
actually filter caps aren't that expensive to replace. a filter recap job which some people seem to dread is actually only $40 dollars in parts and an hour bench time even for a big amp like a marshall 100w plexi. if you're handy you can do it yourself. i've messed with using caps of different values to experiment with tone changes. it's a simple procedure involving soldering 3 wires.
Indeed, agree! But most people don't like doing that stuff. The big amps aren't really a pain, it's the smaller ones where you have to remove boards that are more annoying.
there's the lore about using a variac to slowly bring up voltage in the caps...really, the parts are n't that sensitive. there's a horror tale about needing to bring new caps up slowly or else you'll 'blow holes' in the electrolytic...and they will never sound right.
You're more likely to simply provoke a short like KB0NES outlined, and yes; there is solid science to bringing them up slowly. Will you get away without doing that? Sure, most of the time, yes.
fender didn't do any of that stuff, ever. they built the thing and then plugged it for testing at final inspection.
Despite being an avid lover of Fender kit; they should not be cited when it comes to capacitors in amps. Leo Fender was pretty much the reason that we have standby buttons on amps - and while it's a great feature for muting, swapping cabs and leads, etc - it was to prevent damage because of using underrated capacitors. If you think nothing ever exploded on Leo's workbench, you've probably got another thing coming...