The Steel Guitar Forum

My old Evans fet500HV filter caps (big blue ones w/screw terminals) are 4800(farads or milli-farads? no letters after 4700) @50DC. I'd like to replace them but all I see available anywhere are 4700@50. Would that work?

Steven, its probably micro farads {uf}..And yes the 4700 will work fine..

I have replaced several old Peavey Caps that were originally 5000uf..Now, Peavey only has the 4700 for replacements and they say its no problem..

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Jerry Wallace-2001 Zum: D-10,8+6, "98 Zum: D-10,8+8,Nashville 1000,Session 500 ,Session 400 head only amp,Tubefex,ProfexII, Artesia, New Mexico
http://communities.msn.com/jerrywallacemusic http://www.jerrywallacemusic.com

Steve--for my info, why are you replacing them? My Evans is real fuzzy sounding when I turn it on. It takes around 5-10 minutes to clean up and even tben there is a little low-key residual distortion. It's my best uninformed guess that it is a cap issue. Does this have any similarity to your situation?

You probably know this, but it's worth repeating.

When changing Caps, be sure you note the Polarity (+ or -) and replace it properly.

An explosion could result on power up if a Cap is in backwards.

No problems will be encountered, Steve. Almost all the resistors and capacitors in an amp are rated "plus or minus 10%". Some filter caps even 20%. Before replacing the cap, let the amp sit about 5 minutes (with the switch on) so that the caps will drain completely. Then before doing any removal, short the terminals out with a screwdriver...to make sure they're discharged. Filter caps can give you a nasty shock if you don't!

Thanks everyone.
Jon...I'm mostly trying to clear up various hum problems. Some to do with reverb...some not. Since it's an old amp('80), I'd like cover the bases with cap upgrades as much as is possible with a ss amp. There's a very helpful thread further down "more on capacitors for fender twin"(april 16) you should checkout in case you havent. Yuoll find some good sources for caps there too. I understand distortion problems could be due to transistors. Ed Buffington with Evans still has replacements if thats the problem.

Jon,

I'm used to dealing with filter caps in Marshalls and Fenders, so I've never fiddled with an Evans before even though I have one....having said that, I usually equate filter cap problems, either gone or leaky, with an enormous dreadful hummmmmmmmmm....that's usually the first clue to a filter problem

Just guessing here, but your low level distortion you describe sounds more like either dirty effect loop jacks or a bad FET....the former is easy, just spray some contact cleaner on a 1/4" plug and go in and out to clean the jacks....my guess though is probably a bad FET.

Hope this helps

PMS

Thanks for giving it some thought, Patrick. Oh--and thanks Steven for your response.
With this amp, it is pretty fuzzy--like dry and cotton-mouthy, morning after sounding when I first fire it up. In around five minutes it pretty much cleans up with just a bit of residual harmonic distortion. It is low enough in the S/N spectrum that it is only bothersome when playing pretty softly. Even at its worst it is still playable but I sense that the day will come when I will need to ship it to Ed B. for an overhaul. Fair enough.<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Jon Light on 09 May 2002 at 12:09 PM.]</p></FONT>

Steven,

Here is a source (URL Below) that may help. Also note the 800 number for that company. I checked my Evans amp (FET 500 Custom LV) and it has 6500 MFD (UF) @ 50 vdc (volts DC) capacitors (caps). It was great to see that both Donny and Joey (maybe others) gave you a few tips about safety. I see many post that should have safety tips but do not. I don't assume that you have or have not certain knowledge. The tips are for anyone that reads the post and safety can never be stated too much.It sounds real easy to unsoder a few wires and replace the caps but if not done correctly you will out-scream a cat in a dog fight. It's not so bad if you you have long hair and like it curly.

You may have your amp unpluged for weeks before you work on it but please understand that the caps can hold most of it's charge for very long periods. A well designed amp should include bleeder resistors that will slowly discharge the caps when not in use but you have no way to ensure that the bleeder circuit is working. (without testing it)

When Peavey states that it is OK to put in the 4700 MfD caps instead of 5000 MFD(UF) it is because there is a there is usually a 20 % tolerence (as stated earlier in the post) If we were to use 5000 as an example and take 20 % we would get 1000. As you can see we can use either a 6,000 or a 4,000 MFD (UF) (I have never seen either so we choose the next closest thing).Then the question becomes should you move up or down. If you go up it increases your cost and does not guarantee that you gain in performance.(In any power supply there is always a limit at which any increase in UF will not provide any performance gains.)

For the @50 part. Now we are talking about the working voltage of the cap. You CANNOT go lower. The tolerence is usually 20 % . The output DC voltage from a well designed power suppply can range from - 5% to + 20% (you are still within range) You can go higher than 50 VDC. Of course, as you go higher so does your cost. Also the physical size of the cap may increase and cause mounting problems.

Not all caps are made equal. I would suggest a quality brand name such as Mallory. (there are others)

It may have been stated before but never too often. When working on any electronic device
you should work with one hand in your pocket (not grounded anywhere) and use the other hand to do the work. If something does go wrong you will live to tell us about it.

Also I agree with Patrick (and maybe others) in that changing the caps will not help with
the distortion problem. If you had a hum problem then sure, the caps would be the first components suspected.


If you have or access to (or maybe a friend with) a audio signal generator and an Oscilloscope it will be a great asset in trouble-shooting your problems. If not, take it to the pros.
http://www.galco.com/default.htm?/kwpages/MALY/CAPA-0106.htm

Bob



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Thanks for the tips and site Bob. I take it Mallory comparable to Sprague for quality? I've seen some real high end electrolytic caps about that size called "Black Gate" if you've got burnable money. Youd be out over $200 for a pair. Not in my budget, but I do wonder if they would produce any improvement in sound/performance. I dont really know how influencial power/filter caps are in regards to sound/tonal characteristics. Connecting other more "musical" type caps of say 10% value or so(same voltage) in parallel with the big ones as suggested in another thread sounds interresting and safe enuogh to try.

I tend to think that $200 caps in the power supply would be wasted money. These filters aren't in the signal path, and while they may be used in some really high-end equipment, putting them in a musical instrument amp would be like putting 104-octane gas in your lawn mower. It might give you a "warm feeling", but the only real difference would be noticed in your wallet!

What Donny said. Buy a common brand electrolytic. There is no such thing as a advanced sonic quality aluminum electrolytic. Svante Arrhenius defined how much an electrolyte degrades with temperature and time in the 1920s. Physics has not changed. I am also outraged about other internet suppliers like http://www.angela.com. This is a complete and total rip off. You really think the composition of solder can make a difference in your sound?

Bottom line, aluminum electrolytics degrade with time just like brakes on your car. Some newer multimeters have a capacitance meter built in. Buy one, and check the capacitance and replace them if they are significantly lower then the original value (open circuit).



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Terry Downs
http://nightshift.net
terry@nightshift.net

Good. Little by little the education comes. Now...to learn to trace which are the "signal" caps and which arent(as regards to cap uprades for tone sake that is) I mean...all those little ceramic caps on the preamp circuit board couldnt be all signal path right? Those are supposed to be the worst for tone quality.Too many pesty questions. Just thinkin out loud here. I'm sure the amp book to enlighten will arrive soon.