replacing filter caps in vintage amps

[shortcircuit]

Should you replace the filter caps in vintage amps just because of age ??

[Chuck H]

They should be replaced if they're bad.

To take it a step further, what qualifies "vintage"? I wouldn't consider a Marshal Silver Jubilee a vintage amp, but others might. I would certainly consider that the filters might need replacing though. Any amp with filters over fifteen years old is on bonus time. Some caps seem to hold up for a loooong time. 50+ years of service has been reported in some cases, but that's really extreme. Most are closer to twenty years of service when the caps need replacing. Some vintage amps have BAD caps in them and just go on operating anyway because of the nature of the failure and the stubbornness of the owner and that can skew opinion on the matter. I've actually heard this a lot at small, live shows. Some caps used in amps from the the last thirty years can't reasonably be expected to perform well much after ten years. My opinion is that if the amp is a player then it should have reliable caps in it. That pretty much excludes the original caps in a vintage amp because at that age they simply can't be counted on. They may be fine, but they're past their typical usable life span and there's a show to play. If you only play at home and fancy the idea of an "all original" amp AND the amp isn't humming or making any strange sounds associated with filter cap failure then you have all the time in the world if they fail. So don't worry about it until it needs attention. And I know everything I've written only parrots what's been said all over the place and causes questions like this in the first place. But that's how it is. My own personal stance on the matter is the damn caps are old. If the amp is going to be played at all then it should have known good parts in it for safety reasons if nothing else. Let me put it another way. I would never remove the original tires from a 32 coupe that was going to be displayed in a museum, but I would never drive the car on public roads without putting on new tires even if the originals looked fine.

[Enzo]

I think the more recent an amp, the longer its caps will last. Caps from 50 years ago usually need replacing. New caps today may not need replacing in 50 years. Cap technology has steadily improved over the years. 1970s caps might have needed replacing in the 1990s, but I am not so sure 1990s caps need replacing now. At least not in general.

[Mick Bailey]

The main exception being if its a Fender Deville/Deluxe series with those leaky Illinois caps that develop yellow crud around the +ve terminal. I do more PSU recaps on 90s and later Fenders than any other amp.

[shortcircuit]

They should be replaced if they're bad.

To take it a step further, what qualifies "vintage"? I wouldn't consider a Marshal Silver Jubilee a vintage amp, but others might. I would certainly consider that the filters might need replacing though. Any amp with filters over fifteen years old is on bonus time. Some caps seem to hold up for a loooong time. 50+ years of service has been reported in some cases, but that's really extreme. Most are closer to twenty years of service when the caps need replacing. Some vintage amps have BAD caps in them and just go on operating anyway because of the nature of the failure and the stubbornness of the owner and that can skew opinion on the matter. I've actually heard this a lot at small, live shows. Some caps used in amps from the the last thirty years can't reasonably be expected to perform well much after ten years. My opinion is that if the amp is a player then it should have reliable caps in it. That pretty much excludes the original caps in a vintage amp because at that age they simply can't be counted on. They may be fine, but they're past their typical usable life span and there's a show to play. If you only play at home and fancy the idea of an "all original" amp AND the amp isn't humming or making any strange sounds associated with filter cap failure then you have all the time in the world if they fail. So don't worry about it until it needs attention. And I know everything I've written only parrots what's been said all over the place and causes questions like this in the first place. But that's how it is. My own personal stance on the matter is the damn caps are old. If the amp is going to be played at all then it should have known good parts in it for safety reasons if nothing else. Let me put it another way. I would never remove the original tires from a 32 coupe that was going to be displayed in a museum, but I would never drive the car on public roads without putting on new tires even if the originals looked fine.

excellent response , after posting I came across a post from Randall " replacing 40yr old filter caps " was impressed with Enzo's reply there also. Thanks

[Leo_Gnardo]

I think the more recent an amp, the longer its caps will last.

As you say, "in general" true. But I have found some exceptions. Just last week I was presented with a nearly new Mesa JP-2, a very versatile amp crammed with circuitry. Complaint: it blew the power fuse, accompanied by a smoky odor. One of the main hi voltage caps had flat out failed, it's part of a series pair 220 uF. Made by BMI, presumably the successor to Sprague Atoms, their products are respected. But here we clearly had a baddie. I replaced both with 220uF/350V caps from Ruby - same as the tube company - I've been using their caps for years with scarcely ever a problem. Cheap fix but who would expect a cap only two and a half years old, less than two years in use, to go kablooey?

Add to that an occasional Illnoise main or second filter in Blues Jr's, HotRod Deluxe, RI Deluxe reverb, with 8 to 18 years in use.

[stokes]

Funny thing about BMI.They bought Sprague and now make the Sprague Atoms and the BMI's at the same plant on the same machines,so they are essentially Sprague Atoms,re-labeled.But the BMI's,if you can get them are 1/2 the price.Only place I know of to buy the BMI's in small numbers is from Mesa,but in limited values.As in only the values Mesa uses in their amps.I started using F&T's over ten yrs ago,when the price of the Spragues went out of control,I like them and have had good results.

[Mick Bailey]

With regard to the original question, don't overlook all the other caps in a vintage amp. DC leakage from coupling caps is often subtle and subversive and can make an amp sound really bad. The problem is you start off with a really nice amp with all of its original parts and then slowly replace most of the caps. So, maybe the reverb doesn't sound as good as you think it should, or the trem doesn't start straight away or disappears when the rate is turned down. Maybe you get a way-too-early breakup, or loss of volume. Any of these can be down to a leaking cap. Out of interest I was working on an amp this morning where the reverb wasn't working and the coupling cap from the previous stage was leaking 70v onto the grid of the driver tube. Not good, but a cheap and easy fix.

[Leo_Gnardo]

With regard to the original question, don't overlook all the other caps in a vintage amp. DC leakage from coupling caps is often subtle and subversive and can make an amp sound really bad.

True that! Bias filters gone bad can wreck perfectly good output tubes too, and even destroy transformers in extreme cases. Just had a '72 Marshall 100W head come thru, and it couldn't raise enough bias voltage to keep its output tubes from going into the red zone. Quick swap of the two 10 uF bias filter caps and all is good. Better than good in fact, even though the output tubes are the crappy early 90's chinese EL34 with splints welded to the plates, it turns out a clean 120W and sounds enormous, what you'd expect from a 100W Marshall.

Funny thing, my cap meter showed 16 uF on each of these caps, and no leakage. Swapping in new ones, the bias voltage increased from -32 to -45V. So . . . don't always depend on your meters.