changing caps in an amp...

[mynameisjonas]

i know very little of how the different components of an amp work, and what they bring to the sound, and i´ve often heard people suggesting changing the caps as a way of improving the sound of an amp, so my question is:
why, how, and with what should i replace which caps in my SF twin reverb, for instance?

[DarrelT]

Careful Jonas, caps can KILL.

[mjet]

Careful Jonas, caps can KILL.

Darrel is right - caps can retain current long after the amp is turned off.

From what I've gathered there's little reason to change them for a particular change in sound, but they do get old so when most people buy vintage amps, a cap job is pretty much starting point number 1. But again, that's more of a routine / preventative maintenance type deal, rather than something done to impact tone (like trying various brands of tubes).

[mynameisjonas]

don´t worry guys, i´m not about to go jumping into my amp with my soldering iron
and i know the drill of about pulling the power chord with the amp still turned on, and playing ´til it goes silent..

but let´s say my amp has really old caps, what are the symptoms?

for reference, my friend has a 78/79 twin (mine´s a 75) that sounds so much more alive and sparkling than mine, even though i recently had new tubes put in. mine sounds really tired compared to his, the lows are muddy and the highs are dull and kinda muffled.

[Jay]

Filtering capacitors tend to wear out and will allow all sorts of bad tone to creep into an amp. These are the really large caps (lay down under the pan in a Fender and they stand up like a tube in a Marshall) that remove excess ripple and supply your tubes with the proper operating voltages after converting the AC to DC.  Worn out ones can make an amp sound pretty bad. The others are generally only a matter of flavor but will drift tolerances over the years or just plain go bad and need to be replaced as well.  And although caps store electricity, it's not JUST them specifically to be afraid of.  The entire amp has current pouring through even after it's shut off.  That said, it's not rocket science to bleed any remaining voltage from the amp after it's off and unplugged and I think you could handle that part Jonas.  You just HAVE to be careful and methodical.

[Vinkie]

... but let´s say my amp has really old caps, what are the symptoms? ....

The main symptom is loud 60/120 cycle hum (or 50/100Hz over here in Europe). This hum muddles up the sound even if it's not that loud by itself.
A quick test for the filtercaps is to play Bb and or B chords through the amp: if the filtercaps are dead they'll sound out of tune and/or suffer weird phase effects.

Although recapping isn't a modification (ie. it doesn't change the intended sound of the amp) a recap with properly spec'd caps will often improve the sound a lot and solve other issues like scratchy controls, bass farting out etc.

[Jay]

don´t worry guys, i´m not about to go jumping into my amp with my soldering iron
and i know the drill of about pulling the power chord with the amp still turned on, and playing ´til it goes silent..

but let´s say my amp has really old caps, what are the symptoms?

for reference, my friend has a 78/79 twin (mine´s a 75) that sounds so much more alive and sparkling than mine, even though i recently had new tubes put in. mine sounds really tired compared to his, the lows are muddy and the highs are dull and kinda muffled.

The power cord trick works but its not foolproof.  I would reccomend getting an inexpensive ($20 or so should cover it) muiltmeter.  You'll need one that can handle at least 450v. That way you can measure voltage to make sure it's ALL bled off even after pulling the plug and playing.  Sometimes there's still enough electricity left in the amp after doing that to shock you.  Probably won't kill you at that point but it might still hurt.

[pullover]

check out the Torres Amp Overhaul Kit

http://www.torresengineering.com/fenabovkit1.html

and the Mod kit, (No Twin Sorry)

http://www.torresengineering.com/tubampkitmor.html

A sf to bf mod article, that tells exactly which caps to get rid of, has some great links

http://www.unclespot.com/FenderBF.html
http://www.unclespot.com/AmpINFO.html

theres a lot more articles on this, just search blackfacing a silverface on google.

Tube amp basics
http://eventcom.net/torresgraphics/fullbasicsweb.pdf

"Dscharge the filter caps by shorting the stored current to ground. The safer and
recommended method is to connect a 10k two watt resistor to a pair of insulated alligator clips.
Tape it all up so there is no exposed metal except the ends of the clips. Attach one clip to the +
(plus) side of each filter capacitor (under the amp on Fenders, in a long metal can) and touch the
other insulated alligator clip to ground on the amp chassis. Be sure you aren't touching the metal
of the alligator clips or the amp chassis. This will discharge slower, safer and with less fireworks.
Amps will discharge themselves over time. Small amps will discharge in about four hours
(to be safe) but big powerful amps may have power supplies that do not have “discharge
circuits,” and can take 12 hrs or more before they are safe."

[Jay]

check out the Torres Amp Overhaul Kit

http://www.torresengineering.com/fenabovkit1.html

and the Mod kit, (No Twin Sorry)

http://www.torresengineering.com/tubampkitmor.html

A sf to bf mod article, that tells exactly which caps to get rid of, has some great links

http://www.unclespot.com/FenderBF.html
http://www.unclespot.com/AmpINFO.html

theres a lot more articles on this, just search blackfacing a silverface on google.

Tube amp basics
http://eventcom.net/torresgraphics/fullbasicsweb.pdf

"Dscharge the filter caps by shorting the stored current to ground. The safer and
recommended method is to connect a 10k two watt resistor to a pair of insulated alligator clips.
Tape it all up so there is no exposed metal except the ends of the clips. Attach one clip to the +
(plus) side of each filter capacitor (under the amp on Fenders, in a long metal can) and touch the
other insulated alligator clip to ground on the amp chassis. Be sure you aren't touching the metal
of the alligator clips or the amp chassis. This will discharge slower, safer and with less fireworks.
Amps will discharge themselves over time. Small amps will discharge in about four hours
(to be safe) but big powerful amps may have power supplies that do not have “discharge
circuits,” and can take 12 hrs or more before they are safe."

Dan Torres is sketchy at best.  I seen some real horror stories on the amp building forums.

As for the aligator clip...  I jsut added this resistor stright in to the 18watt I built. It bleeds pretty quickly once the amp is unplugged but I still always check for extraneous voltage before I start dicking around inside.

[Maggieo]

Dan Torres is sketchy at best.  I seen some real horror stories on the amp building forums.

That's hearsay and, frankly, bullshit.

I know Dan personally, and he's worked on a bunch of my gear and he's as good as anyone in the business.

IMO, the biggest problem Dan has is idiots who try to follow his instructions, but are too stupid to follow directions and then blame Dan for their stupidity.

[pullover]

I know Dan personally, and he's worked on a bunch of my gear and he's as good as anyone in the business.

IMO, the biggest problem Dan has is idiots who try to follow his instructions, but are too stupid to follow directions and then blame Dan for their stupidity.

I agree MaggieO. I don't know dan or the quality of his personal work, but if you buy a kit, install the parts, and it doesn't work, I don't see that as his fault. Anytime you open up your amp or guitar you are risking screwing something up, and having to fix it, and by deciding to do the work yourself that responsibillity falls on you.

[Jay]

To be fair I did some more looking around and apparantly Dan doesn't even own the shop anymore (sold out a few years ago) but it uses his name still. I guess that's how it goes when you sell?

Anyway, most all of the stuff people were complaining about were unfulfilled orders (and never gettign a refund) and poor customer service.  But that's all moot really since it has nothing to do with the actual Dan Torres.  I take back the sketchy comment.