cap replacement question

[rexindigo]

long time I thought it was just yesterday, but i have to accept the fact that i bought my beloved Musicman 110 RD 50 thirty years ago.

not enough that this makes my thirty years older, but i just realized that most experts say, that electrolytic capacitors are good for about ten years.
Now I'm wonderig how i can determin if the caps are to be replaced?
(the advantage of the thirty years gone by is, that if there is an issue pointing to the replacement, i am now able to do this by myself..;-)

thank you for any comments!

Musicman 110 RD 50 is a hybrid amp with solid state preamp and a 2x 6L6 poweramp. its got a Fender Type Brilliant clean channel and a 12ax7 driven channel for overdrive sounds called "limiter channel"

[stokes]

There are a lot of differing opinions on the subject.I have yet to hear a valid one for not changing them.Over 30 years ago I was taught that they should be changed after about ten years,I was shown an advisory by a supplier from either Sprague or Mallory once,years ago,that advised not to sell caps that were on the shelf 10 or more years.I have always adhered to this "rule of thumb",my own amps get them changed about 7-8 years.When I do a cap job for somebody,I always give the guarantee that even if the amp seems to be okay,if the caps are over ten years old,they will notice a big improvement in the response and an overall tighter sound or I will replace the old caps and they pay nothing.I have never had to put the old ones back.As the caps slowly degrade,the deterioration in the amps response is not as noticeable until it becomes so severe that the bass starts getting real sloppy,you kind of get acclimated to the degradation a little at a time.I think after thirty years it would be advantageous to change them.Caps have a finite lifespan and dont last forever,if you've ever seen what they do when they spill their guts after a total failure,you wouldnt have waited thirty years.Oh,and be sure to use good quality caps,the Xicon and IC's and the like are really inferior in quality and tone.I just had a year old Fender Blues Deluxe in with a bad hum.As soon as I opened the back panel it was obvious that the cause was the IC electrolytics oozing their guts,not just one or two,but all four of them.I like Sprague and F&T's,the latter should be readilly available in your area.

[Enzo]

AND I am on the other side of that fence, and we don't need to retrace previous discussions.

I would add, that when a part maker says don't sell a part that sat on the shelf for 10 years, it is more about not having ben in use all that time than it is simple age. Like tires on a car. they can last ten years easily if you drive on them, but not if the car is up on blocks all that time.

I would also add that today's caps are better than those of 30 years ago. SO I don't doubt that brand new modern caps sound better. They would sound better than brand new caps of 30 years ago did, even with zero deterioration.

[rexindigo]

Well, the two answers point in different directions. I must admit for a couple of month i had the feeling that this amp did not sound as great as it did when i first bought it.( But this can point to getting deaf after all...)
Now if I replace the Caps, would You advise me to replace all Electrolytics (assuming that foil caps need not to be replaced?) or only the ones handling high voltages?

[Rick Erickson]

I would recommend replacing them all, the electrolytics that is... I've seen more failures with the low voltage caps in Music Man amps than the high voltage ones. Keep in mind - they are all deteriorating at about the same rate - entropy and all that... I've recently been going through some 67-69 Marshalls for an old friend. He wanted to keep them as "stock as possible", so I only fixed the necessary items and told him that the caps were on borrowed time. He finally had me replace the filter caps on his #2 amp and after he heard the sound with new caps it has become #1.
He just picked up another, so I will probably be replacing the filters on both his spares soon.

RE

[stokes]

I know we've been over this before,Enzo.Just to clear up what I said about the bulletin,I didnt mean I was shown it 30yrs ago.I was shown that by probably the last supplier in downtown Manhattan probably back in '98 or '99.I dont think cap manufacturing has made any great leaps since then.I have had a parade of Boogie amps come thru in the last year or so,after I did a cap job for a guy from Westchester.He has recommended me to at least a dozen Boogie owners from all over the tri-state area,himself,I have easilly done 60+ Boogies in the past year or so.Every one of them were amazed at the improvement in the amp,my point being that these amps didnt have 30yr old caps,even the ones that came close to 30 yrs still had the same blue Sprague 30uf's,I doubt they are any different than what Sprague is making today.To me changing caps is a preventive maintenance thing as well.I understand a cap sitting on a shelf with no current applied will dry out.But if an amp is used for a few years then left sitting for a year without use,how much have they dried out?If there wasnt a definate improvement in tone after changing them,I likely wouldnt have as strong an opinion on it,but that,and having cleaned a couple of amps with exploded caps,it just makes sense not to wait till that happens.And like I've said before,I still havent heard a valid point not to do it.

[rexindigo]

Thank you Stokes, Your reply reminded me that my Mesa caliber 50+ is also at least fiveteen years old. So i ve got a new amp project called:
- maintenance on my factory build amps!
(maybe cap deterioration is the reason why i like my new build amps more than my once much loved oldies, i will certainly know after the cap job is done!)

[Enzo]

Your amp probably will sound better. The only way to really determine cap deterioration though would be to replace the caps with new of the exact same types.

[Robert M. Martinelli]

shelf/operating life considerations

As a rule of thumb, replacing the caps after 30+ years is surely a good practice;

I would like only to distinguish between shelf and operating life: electrolytic capacitors reach their big capacitance values thanks to the use of metal oxides ( eg. aluminum ), and an electrolyte ( hence the name ) which keeps the oxide thickness constant ( and thus the capacitance ).

What happens with shelf life is the electrolyte dries out and ( I have witnessed it ) when you try to put in a cap which has been on a shelf for years ( without knowing it ) you' re in for a big surprise- The same thing happens when a tube amp has been not used for many years, you switch it on and - BANG! - one or more of the filter caps go off...

On the other hand I' ve seen caps with 30+ years of service still performing well, and, measuring them, I' ve found the capacitance to be right and the ESR ( equivalent Series Resistance ) still surprisingly low, indicating the cap' s good state of health.

It then seems that the loading/unloading process associated with working help maintain the electrolyte active, prolonging caps life.

Hope this helps

Regards

Bob

[stokes]

"It then seems that the loading/unloading process associated with working help maintain the electrolyte active, prolonging caps life".
Sure,but caps still have a finite life span,and even tho the 30 year old caps may seem to be doing their job,there isnt an amp with 30 year old caps that wont sound better with fresh ones.And why wait till they spew their guts out?

[Robert M. Martinelli]

30+ years caps deserve "retirement"

Of course I agree, I started my previous post with :

"As a rule of thumb, replacing the caps after 30+ years is surely a good practice"

I was just wanted to analyze and make clear the differences between "shelf" life and "operating life" - I absolutely agree that 30+ years old caps NEED and DESERVE a peaceful retirement, ( otherwise they could "form an union" and maybe sue me..... )
Regards
Bob