amp capacitor replacements? (N00Bish questions)

astro · Post by **astro** » Fri May 23, 2008 4:22 pm

A little while back, I bought a 1980 Fender Concert II combo. I retubed it with JJ's and it sounds TEH SEHX.

I've heard that the capacitors in amps need to be replaced after a number of years. How do I know if my amp needs the caps replaced? The amp still sounds good. I looked at the chasis, and I think they're the original caps, but I ain't even close to being an expert on the subject, so who knows.

What happens if the caps go bad? Will the amp just sound bad, or does it become a fire hazard? What is a capacitor's life expectancy?

If they need to be changed, I'll have a tech do it, since I don't want to kill myself with any voltage lingering inside the capacitors.

Justin J · Post by **Justin J** » Fri May 23, 2008 4:44 pm

yeah, it's the filter caps that need replacing. the big, fatty electrolytics with enough voltage to kill you. i've heard you're supposed to do it every 10-15 years.
i don't know how much a tech will charge to do it, but the capacitors themselves shouldn't cost more than a few dollars.

astro · Post by **astro** » Fri May 23, 2008 4:48 pm

what happens if they don't get replaced?

Justin J · Post by **Justin J** » Fri May 23, 2008 4:50 pm

i think at some point they can explode. i'm not sure how likely that is.
usually they just sort of stop working.

filtercap · Post by **filtercap** » Fri May 23, 2008 10:21 pm

What Bubbles said the first time, + what Bubbles said the second time. It isn't just the filter caps you'll want replaced. There are a half-dozen smaller "bypass" caps that are also electrolytics and will need replacing eventually too. Might as well do the whole lot at once while the amp's open.

In the ooga-booga world of tube amps, bad old caps are said to be responsible for all sorts of things. Poor bass response, diminished volume, low headroom, more line hum, ghost notes, drowsiness, irritability, poor gas mileage, identity theft, global warming, divorce, spontaneous combustion, and various mojo dysfunctions.

There are also non-electrolytic caps in your amp (film caps and/or ceramic caps). These don't wear out the way the electrolytics do, and should be fine as-is.

astro · Post by **astro** » Sat May 24, 2008 5:08 am

Thanks for the responses!

Should the replacement be automatic after a set number of years? Or can I wait until symptoms develop? When you guys say "explode", do you mean that the cap just bursts, or are we talking mushroom clouds here?

filtercap · Post by **filtercap** » Sat May 24, 2008 7:07 am

astro wrote:Should the replacement be automatic after a set number of years? Or can I wait until symptoms develop? When you guys say "explode", do you mean that the cap just bursts, or are we talking mushroom clouds here?

It'll take out most of your block. But you won't feel a thing.

I've never seen/heard one pop. They do this if the electrolyte overheats and basically boils inside the capacitor. Don't expect anything cool like flames, twisted metal, or helicopter video of your devastated neighborhood on the news. Just electrolyte splashed around inside the amp chassis, where it will eventually corrode whatever it touches. If there's a short when this happens, it might endanger your power transformer.

Usually exploding is how they respond to being wired in backwards (they're bipolar... pun intended, if you like). If they've been working OK for years, they'll likely just dry up eventually and stop doing their thing.

There's no set amount of time, but every 10 years or so is recommended. You can wait until symptoms develop, but on the other hand, your amp might have symptoms already that you aren't aware of. For example, if one of the bypass caps has been dead for years, the amp will still work, but changing it may give you a bunch more gain you didn't think the amp was capable of.

Ninja Mike 808 · Post by **Ninja Mike 808** » Sat May 24, 2008 9:18 am

Is it every Electrolytic? Also, how do you not kill yourself?