What are the symptoms of an amp needing a cap job?

[Laheart]

I have three vintage Fender's (Concert II, Super Reverb and a Twin) and, to me anyway, they sound great but I keep reading about getting guys getting/needing cap jobs. What are the symptoms of an amp needing a cap job?

[teletroy]

off the top of my head, lower volume than normal , ugly distortion when there should be none, Extra Hum, low voltages.. There's probably a zillion more, someone will chime in.

I had a 76 SFDR that I thought sounded great, a few days before a big show I dropped the chassis and took off the cap can cover and one of my caps had burst and another looked like it was getting ready to. I replaced all my electro caps on the spot. The amp never sounded better after that.

If the amp is over 20 years old, it's probably time unless you aren't playing them and keeping them as museum pieces.

[Laheart]

Thanks for the reply. I purchased all three of the amps from the same person who had not used the amps at all since 1984. They were stored in road cases and look to be in great shape. All of my other tube amps are relatively new. I was just wondering if there were a time factor involved. i.e any amp over 20 years old should be recaped or if it was a matter of usage.

[drgonzoguitar]

The electrolytic capacitors that filter AC "dry" out after time---even when they are not being used. You should change your power caps every 10 years, IMO.

[jay42]

You might also notice ghosting. Sounds like you're good for the moment. Were you to do it yourself, it's not expensive for parts. You could do the one you use the most and see if it was worth the effort. In a case like that, it would have been good for those caps, to bring the amps back up on a variac (tubes removed). Too late now.

[rockon1]

Symtoms? - increased hum, loss of low frequency response. I dont agree with modern caps lasting 10 years though. More like 20-30 years. I wouldnt consider replacing caps younger than 20 years old unless there were symptoms. My 86 Laneys caps worked fine. I replaced them as a precaution but there was no performance benefit with the new caps. Bob

[Laheart]

Again, thanks for all of the info. The Super and Twin are both 64's. He bought them at the same time. The Concert II is an 83/84 and it's the one I'm using the most. I heard two other twins in the last month or so, one was a 73 and the other a reissue. My Twin sounds just as good as both of those so I guess the caps are OK. Maybe it would be a good idea to have a tech look at all three just to make sure. I'm assuming that a tech would have some sort of meter or scope to tell if they really needed to be replaced.

[Ronsonic]

Many tech's don't measure caps for goodness. About the only good measure is an ESR meter others will measure for ripple. The latter will miss a few things.

You're listening for soggy bass, ghost notes around the 12th fret, curdling when you play double stops and bends up the neck, excess hum, oscillation and motorboating. My favorite symptom is the decoupling cap in the preamp going bad in a high gain amp. Turns it into a 40 watt analog synth.

One of these days I'll offer a switch for that cap as a mod for my noise oriented customers.