When to replace cap's ?

[6L6C]

I have had a Mark IV since 93 and I know it depends on allot of factor’s but is there any sort of loose time table when to replace cap’s?
I am new to the forum and have read a fair amount of threads about people replacing caps, so it ‘s just making me think. By the way my amp is performing perfect it is just I’m the type of person that likes to do preventive maintenance (don’t like to wait for problems)
And one other question I’m not to clear on. What are some of the sign’s of caps going bad?
Thanks
John

 

[Shep]

when you start to loose your tone is the biggest sign..if there is goo coming out of them then thats a even bigger sign..

 

[AtomicMassUnit]

When you start to hear out of tune notes underneath the ones you play, and you hear excessive hum in the amp.

 

[stokes]

Its a good idea to change them after ten years.Even if you dont notice any deteriation in the tone,you will notice an improvement with fresh caps.The degredation in tone comes gradually,and may not be noticed till it is severe.When they get over ten years old the failure is often sudden and if the cap explodes it makes a mess.They also tend to become "leaky",that is,they leak current to ground.This causes stress on your rectifier and PT,and over time can cause failure of both of these.I change the caps on all my amps after 6-8 yrs.Its good insurance,I dont ever want to clean up that mess again.

 

[alistair]

after filter caps, are they any other caps it is worth changing?

 

[Elpelotero]

great advice here guys!

 

[stokes]

Any electrolityc caps.The small bias caps,and if you have any electro's on the cathodes,but I have never seen electro bypass caps in a boogies preamp cathodes.

 

[Shep]

hey stokes, were do you get your main filter cap's from? i think i should put some new one in my mk iv..

 

[stokes]

For the 220uf @300v I like the F&T's.Sprague doesnt have them in that size.For the 30uf@500 I use the Sprague.I dont like the Illinois that Mesa uses,although the name seems to imply they are made in the USA they arent,Taiwanese I believe.Mesa uses Spragues for the 30's.I get them from Newsensor,only because they are local,but you can find them cheaper.If you are going to change caps,I would recomend changing all of them.including the small bias caps.Be sure to form them before putting them under a full load.

 

[6L6C]

Thanks for the input everyone!!

And "stokes" thanks you for the details!
I have a few amps that need to be done, oh well one at a time after the holidays.
But like I said I like rather do PM’s (preventive maintenance)

 

[psychodave]

For the 220uf @300v I like the F&T's.Sprague doesnt have them in that size.For the 30uf@500 I use the Sprague.I dont like the Illinois that Mesa uses,although the name seems to imply they are made in the USA they arent,Taiwanese I believe.Mesa uses Spragues for the 30's.I get them from Newsensor,only because they are local,but you can find them cheaper.If you are going to change caps,I would recomend changing all of them.including the small bias caps.Be sure to form them before putting them under a full load.

How do you normally form them? I changed all the filter caps in my 4 Marshalls and just turned them on and started cranking away.

 

[stokes]

There is some debate as to whether or not it is necessary to pre-form caps.Some argue that only old caps need to be formed,because the electrolyte gets dry.To that I can only say that I have never seen a manufacture date on a cap,so you have no idea how old the new cap actually is so I always pre-form them.To form the cap you bring the voltage applied to the cap up slowly with a variac.I like to start with the variac set at 40 and raise it every hour or so by 10 until you have it up to full voltage,takes 6-8 hrs.Some say merely turning the knob slowly is good enough,I learned to do it the slower way I described,I cant say for sure one is better than the other,but that is the way I learned.If you dont have a variac you can also plug the amp into a light bulb in series current limiter for a number of hours,I would recomend leaving it over night.The idea is to let the electrolyte slowly heat up till it forms before giving it the full voltage.Back in the old days,even older than me,some used to rig a light bulb type "oven" and just place the caps in there to cook them before installing,although I dont think that is as effective.I am a firm believer in pre-forming caps,it is a very important part of your power supply and I like to know they are performing their best.I actually made an apparatus I use to form up to 25 caps at once,so all the caps in my stock are ready to install,I dont have to have somebody's amp sitting on my bench for 8 hours.

 

[Harry the Horder]

and that's a 100 watt light bulb in series.

 

[kdove]

I have not heard of this ... I have an old boogie and would like to inspect mine. What do these caps look like? What to look for? Any pictures?

 

[user 2126]

What do these caps look like?Any pictures?

Check this: http://priceamp.home.comcast.net/capjob.htm

 

[Blueshaggis]

This is new and unhappy news to read. I didn't know I might
need to change out the capacitors on my Boogie, bummer. It
sounds fine now. How much should I expect to pay a tech to do
this? I'm not going to go "under the hood" myself and chance
screwing things all up on an expensive Boogie. I don't know how
old mine is but I bought it used about 11 years ago.

 

[stokes]

Kdove,there isnt always anything to look for,a cap that has passed its useful age can look fine,till it starts oozing or just explodes.In my earlier post when I said they can become leaky I wasnt refering to them leaking electrolyte,which they sometimes do,I was refering to leaking current,which will make them draw more current than the tranny can safely supply.If you do see bubbling or oozing,you should change them immediately,if they explode they make a real mess all over your chassis,and can destroy other components as well.I wont comment as to what a tech will charge,you would have to ask your tech,I am sure there is a wide range from one tech to the next.If you dont know your way around the inside of an amp I would not advise you to do it yourself.The filters are where the high voltage (+/-500vdc) in an amp is and they can store this voltage after the amp is turned off.

 

[stokes]

Just to update something I said earlier about the current limiter method.I looked for info on this and found that Gerald Weber of Kendrick Amps suggests to just plug the amp into the current limiter turn it on,the light will glow bright for a few seconds when tha amp is taken out of standby mode.When the caps fully charge the light will dim and you are done.Although he prefers the variac method he says this will do if it is all you have.

 

[Shep]

hey i can you tell me how many 220uf/300v and 30uf/500v asre in my mk iv ..i can't be bother to open up my mark as it's in a rack case and the shematic's i have don't have the power supply written down..

Thanks so much..tom

 

[kdove]

Kdove,there isnt always anything to look for,a cap that has passed its useful age can look fine,till it starts oozing or just explodes.In my earlier post when I said they can become leaky I wasnt refering to them leaking electrolyte,which they sometimes do,I was refering to leaking current,which will make them draw more current than the tranny can safely supply.If you do see bubbling or oozing,you should change them immediately,if they explode they make a real mess all over your chassis,and can destroy other components as well.I wont comment as to what a tech will charge,you would have to ask your tech,I am sure there is a wide range from one tech to the next.If you dont know your way around the inside of an amp I would not advise you to do it yourself.The filters are where the high voltage (+/-500vdc) in an amp is and they can store this voltage after the amp is turned off.

So on a '78 Boogie ... I should have a tech just replace outright? There is nothing that can be checked? If I replace, can you recommend good replacement parts? What other parts might need to be replaced due to age on my rig?