SWR Studio 220 Capacitor Question

[Hawk]

I've included two images. Amp belongs to a friend. There are three leads from the two caps on the board and only two are being used. To me this doesn't look like a dual cap, so I don't understand why there is an extra lead. It's not used in the amp and the amp works just fine. Thanks!

[Enzo]

Well, first it looks like a part someone cobbled in there at some point.

That is a physically large part.  If soldered to the board standing up as intended, it is tall and heavy.  Larger caps like that often include an extra dummy pin or two for stability.  it usually has a solder pad on the board for the extra leg, but it doesn't connect to anything.  It is soldered to provide extra strength.  A lot of makers also run glue around the bottom of the cap to glue it to the board for additional strength.

[Roly]

There ain't no way that cap is original, and I'm none too impressed by the workmanship - or lack of it.  Caps of this size must be securely mounted or they will just rip themselves free with normal transport vibration and impacts.

The third leg is an isolated support pin, and in some caps it is more physically robust than the electrical connections.

[Hawk]

Thanks Roly and Enzo. Good info moving forward. Caps were definitely bent to fit into chassis--they can't be stood up  as they would stick about 1.5 " above chassis. Not sure what the orginal caps were but I will find out to satisfy my curiosity.

Questions: The graphic equalizer faders on this amp are in rough shape, full of static, seeming to lose their smoothness and "sticking" ability once pushed downward to their lowest setting (they suddenly speed up as if freed). There are four and one of the far left cuts out the signal when pushed down to the bottom. There are de-greasers, de-oxit products on the market, but they are not cheap! What are the best products in your opinions when it comes to a good FaderLube and contact cleaner. And what would you do, in terms of a fix, for these tired old faders (aside from trying to buy new ones which SWR no longer provides. Didn't have much luck so far trying to locate any).
I live in Canada.
Thanks again!

[Hawk]

Does anyone know where I can find a schematic for the power amp section of an SWR studio 220 bass amplifier?

[Hawk]

Also looking for a decent pre-amp schematic of for the SWR220--the ones I've uncovered so far are blurry when enlarged and hard to see otherwise. You think SWR would have a decent archive of their schematics!

[g1]

  There are a few power amp versions, what are the output transistor types?
Preamp schematic attached.
Deoxit makes a fader lube, as you say it is expensive.  Other types of cleaners tend to change the feel of the faders.  In Canada you can find the deoxit sold by Hosa accessories at music stores.  Alternately you can take the faders apart, use regular deoxit or equivalent, then lube the moving parts with white lithium grease or similar.

[g1]

  I'll just put both power amp schematics up anyway.  Might come in handy for someone in the future  :cheesy:

[Roly]

http://www.eserviceinfo.com/downloadsm/58493/SWR_basic%20black.html

[Hawk]

Thanks g1 and Roly! That preamp schem. is much clearer than the one I have!

Question about eservice. I was nervous about downloading from there as it looks like they will somehow be part of my chrome browser and it would be tough to get rid of it if I didn't want it anymorel Is this a safe site?

[Hawk]

Question about the white lithium grease. Is this conductive? Wouldn't it mess with resistive tracks of the faders?

[g1]

  It's non-conductive in it's normal state.  But you don't want it on the tracks anyway.  Just where you have mechanical contact of moving parts (aside from the tracks and their contacts).  The tracks you would clean with a regular contact cleaner that contains a lubricant, whatever you are using for regular pots.

[Roly]

Is this a safe site?

As far as I know, but then I'm using Firefox.  I didn't see any obscure "I'm happy for you to hijack my machine" tick boxes to untick.  It downloaded directly for me, but I am cautious about sites that send you a "downloader" first because they often try and spin other (unwanted) software on you in the process if you don't pay attention and untick the default extra downloads.

Try Googling "SWR basic black" for alternatives.


Talking of safe, it is good practice to treat all of these compounds and chemicals you use, lubricants, thermal pastes, contact cleaners, etc, as if they are toxic, don't get them on your skin and don't eat or smoke until you have given your hands a good washing.  They are not particularly dangerous, but they won't do you a lot of good either.

[Hawk]

 

[Hawk]

Speaking of caps: I tested both 6800uf caps with my blue esr meter and found one to have a high reading. There is a fair bit of hum from the amp. I will probably go ahead and replace both. However, I do not have a power supply schematic for this amp (don't think one exists). Any suggestions for a "correct value" to use as replacements? There is probably a formula to figure out how to determine proper cap size in the power supply but I'm not sure how to do that....thanks.