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FDP Forum / Fender Amps: Vintage (before 1985) / Electrolytic life span



May 21st, 2016 08:22 PM   Edit   Profile  

Is it really true that these should be replaced every ten years? I've even read 15-20 somewhere. I'm curious what The general consensus is on this. Should you wait till you have a problem to change them or change them out before there's a problem?

Danny Nader


You should have been there!
May 21st, 2016 08:33 PM   Edit   Profile  

Change them out before you have a problem. A tech can test them if you want. But the 10 - 15 yr rule is a good one. Your amp will love you for it.


Contributing Member

American Patriot

I'm on guard these days.
May 21st, 2016 08:36 PM   Edit   Profile  

I've play lots of old Fender amps that had the original electrolytics still there and they were fine. Well, that was years ago when we didn't seem to know so much about this stuff. You can play them when the caps are out of tolerance but it might cause other things, down the line, to go wrong. Before I knew about changing the caps, I had lots of farting and stuff like than. I would say 10 to 15 years is about right but some folks might change them more often. I do not know if they will last longer the more you play your amp. All of my older Fender amps have new electrolytics in them and they are good. Original electrolytics in a 60's amp definitely need changing as well as 70's amps.
Don't wait if you know the age of your caps and they are out of tolerance.
I have never destroyed any of my old Fender amps because of bad electrolytics.
Lots of jabberin' just to say, if you don't know, take your amp to a good tech.

(This message was last edited by BbendFender at 10:37 PM, May 21st, 2016)



May 21st, 2016 09:20 PM   Edit   Profile  

I recently changed out the original caps in my 68 Bandmaster Reverb. One had started to leak and a resistor was starting to burn when I checked it. All is good with it now. I got to thinking that my 67 Deluxe Reverb had a cap job but it's been just over 10 years ago. Can't believe how fast time flies.


Canada, Kamloops

Vintage Amp Hoarder
May 23rd, 2016 05:10 PM   Edit   Profile  

Here is a post I wrote in a different forum recently:
More thoughts on ESR meters and caps:

Over the past few years, during my journey learning about amps, the topic about servicing these old relics is often unsettled. I'm not going try and settle the topic but share my experience. I'm a self educated tube amp hack so forgive my limited perception.

If you talk to a Pro amp tech, all but a scant few in my travels say change all the electrolytics. If they are over 15 years replace them most say. There is electrolytic fluid inside them. I believe "electrolytic" basically means its a fluid that conducts electricity. As caps age, somehow this fluid dries up. This is especially true if amps are stored for long periods without any use. Amps that are used more often, essentially have healthier caps. Not all caps in your tube amp are electrolytic. Some are ceramic or mica, or other dry type capacitors. For example coupling caps, tremolo circuit caps are dry.

Some amp fanatics, especially collectors say most old electrolytic caps are fine. Claiming those who change them just because they are old are foolish. I have heard them say "Send me all your old caps, I'll happily re-use them". I've read several emotional arguments from both sides. The general consensus seems to be if you want an old reliable amp that can be played and gigged, change the caps. Do what's needed. If you want to put it on the shelf and admire its original beauty, leave the originals in. Sounds simple right? I struggle with having an old amp and and rolling the dice whenever I power it up. Will an old cap fail? Could I ruin a transformer if a cap fails? There's 15 amps of power in the plug in your wall. The little 2 amp fuse keeps those 15 amps at bay. Thats all a healthy amp needs so the fuse is just fine. Say an old original bias cap is failing. Or a B+ power supply cap is failing. It starts to allow more amperage thru. The amplifier tries to pull more than 2 amps thru the fuse and the fuse melts. It does what its supposed to do. When your amp starts blowing fuses, something is up. Don't put a 5 or 10 amp fuse in it. If that cap fails with your new 10A fuse in there, now the flood gates are open. You're now pulling 10 amps of current through your amp. Something is going to melt or maybe catch on fire. Quite possibly your original power transformer windings will melt.

This 1959 Twin had a 10 amp fuse it it when I bought it. It had a bias cap that was blown apart and spewed its guts inside the chassis. We can assume the electrolytic caps should have been changed by 1980 at least. I am keeping my fingers crossed when I get back into the amp, the PT is still working.

Back to ESR meters. I am the curious type. I want to be able to analyze old caps. I had fully intended to change all electrolytic caps in this Twin anyway. An ESR meter allows me to check the health of a cap. But not dry caps as mentioned above. Next time I get engaged in a discussion around old caps I'll be better prepared. Lol.



May 23rd, 2016 07:23 PM   Edit   Profile  

Loosing a tranny was my biggest concern when I bought my 68 Bandmaster Reverb. I know the amp was tested by the previous owner because he sent me pictures of the amp and one had the pilot light on. I asked him how long he had it turned on and he said he took it to a friends so he could test it and it was only on less than 10 minutes. First thing I did when I got it was to check the fuse and I found a 3 amp instead of a 2 amp. Pulled the chassis and opened the dog house. One cap had spewed it's guts all over the inside of the cover and a resistor had started to burn. Turned out the tranny was fine after I did a cap job. The plug on the AC cord was very hot after I tested the amp, found it when I unplugged it so checked a little deeper and found that one contact was loose internally and I wasn't getting 120v to the fuse. So I replaced it anyway with a 3 prong. I only changed out the electrolytic filter, bias, and cathode bypass caps. Coupling caps are original and must be good because it sounds really good and is very quiet but it would be nice to know exactly how good they actually are. Some could be close to being out of spec.
ESR meter, yah I want one of those, I could sure use one and they aren't cheap.

(This message was last edited by roadhog96 at 09:20 AM, May 24th, 2016)


Canada, Kamloops

Vintage Amp Hoarder
May 23rd, 2016 11:08 PM   Edit   Profile  

The ESR meter that I have, a Peak model 60 can only measure electrolytic caps down to 1uF. Coupling caps are not electrolytic, and less that 1uF so they cannot be tested on it. The way to test a coupling cap is by testing it for DC voltage passing thru it. It should only let AC voltage pass through. My unsderstanding is you can test coupling caps on a live amp with a DMM. I will be doing this soon.

(This message was last edited by keithb7 at 01:12 AM, May 24th, 2016)



May 24th, 2016 07:41 AM   Edit   Profile  

Looking at the specs of the ESR meter, I see that 1uF is the lowest limit so I that's not going to do any good for those coupling caps like you said. As far as testing the Electryolic caps I haven't, if they are old I just replace them with new and hoped for the best with the new ones. So far I've been lucky but having the right tools to know exactly what's going on is the only way to do it right, luck don't last forever. I only work on my own amps, kind of a hobby, playing and learning to do my own work encluding guitar set ups. I find it interesting and rewarding.


Canada, Kamloops

Vintage Amp Hoarder
May 24th, 2016 08:00 AM   Edit   Profile  

We're on the exact same page Roadhog. I too do all my own work on my own amps and guitars. As a hobby to enhance my other hobby, playing guitar and bass.



May 24th, 2016 08:29 AM   Edit   Profile  

Yah I think more and more people are learning to do their own work mainly because of the expense and the help of the Internet. Years ago we had to go to the library to find any info. Today everything is just a click away. Either way it's worth knowing how to do things without having to rely on someone else. When your a homeowner this is so true. Any work you have done is hundreds or more like thousands.

Steve Dallman
Contributing Member

Merrill, Wisconsin

Age is just a number...mine is big
May 27th, 2016 11:50 AM   Edit   Profile  

As electrolytic caps age, the electrolyte becomes crystallized and no longer "forms" (liquifies) when powered up. This process happens faster on amps that sit, unused.

As caps age, they drift, usually upward in value, very sloppily. As the capacitance drifts upward, sloppily, they drift downward in power handling. Eventually they will fail.

When they fail they will either open up (hum) or short (taking other components with them...perhaps your transformer.)

Replacing electrolytics is normal, routine maintenance.

A 50 year old amp with original caps is like a 65 Mustang with original belts, hoses and fluids.

Would you turn the key?

I've replaced shorted caps, and the transformers they took out. Routine maintenance would have spared those transformers.

Yes, some 50 year old caps are fine. You take the chance with your amp if you've a mind to, but I won't. I've replaced a lot of electrolytic caps over the decades. I've replaced relatively few failed new caps.

Again, this is routine maintenance...like oil changes and cracked belts and hoses.

A collector who demands original electrolytic caps knows little about how amps work.

FDP Forum / Fender Amps: Vintage (before 1985) / Electrolytic life span

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