Why electrolytics in power supply

jwrosenthal

Super Member
Hey guys,

Researching recapping several pieces of my vintage gear (some working perfectly, some not) and I keep seeing that electrolytics are still being used in the power supplies as opposed to the fancier film and poly caps like I have used in Audio section or speaker crossovers.
Why are electrolytics still preferred in power supplies and not poly caps which have a longer shelf life?
 
If you disregard cost, look at the physical size of the replacement capacitor. Modern electrolytics are pretty good, and often people bypass them with a film cap.
 
Two answers: size and cost.
Other than that, films are superior in all counts.
I use film caps everywhere I can.
 
What they said! Absolutely.
I use the MPP’s in my home built stuff where I designed the chassis/case with ROOM. I couldn’t even imagine how funny it would be to try and stuff 4 47uf 630 volt Solens in a fisher, that is hard to even fit .47’s in. Each Solen is almost the size of a beer can! They are fantastic though, where they can be fitted.
 
So would there be a benefit to using film in power supplies? I’ve heard people say that since it’s not in the Audio path and just doing the heavy lifting of the power supply, “good sounding” caps don’t matter there. If I’m taking the time to work on these things, I’m not too concerned with saving $25 on the cost...a few hundred in caps is another story if it won’t make an audible difference.

I want to replace the lytics in my MR71’s, of which there are only a few and was wondering what I should buy (most are disc). The big 3 and the can are only power supply and are very easy to get to and have plenty of room around them. The little ones are Audio path and harder to get to. The power supply are the ones I am most concerned about as I don’t want a melt-down and all seems to be “working” fine right now in 55 year old caps.

And film, not poly?
 
The physical dimensions of film caps can definitely pose issues. I replaced 6μf 600 volt “bathtub” power supply capacitors with 6.8μf 630 volt Solen film caps, and feel fortunate that there was just barely enough room inside each amp for a 0.97”x1.69” tube. A 47μf Solen is 2.09”x2.59”, for perspective. The “bathtubs” remain in place for the sake of appearance, but they no longer function to spec, and were replaced for this reason.
 
Last edited:
People swear they can hear a difference and love them. Other people say those people are crazy and there is no way a difference can be heard or measured. This is a topic that starts forum wars and gets threads shut down, which is pretty annoying. I’ll suggest this; if you’ve got the room give it a try. It certainly isn’t going to make your gear sound worse.
 
The use of film caps in power supplies often compels the use of chokes as well. Cost notwithstanding, film caps simply don't come in values high enough to forgo choke filtering within reasonable size constraints in many applications.
 
We'll hold the debate for replacing standard electrolytics with bipolar for another day ... ;-}
 
The use of film caps in power supplies often compels the use of chokes as well. Cost notwithstanding, film caps simply don't come in values high enough to forgo choke filtering within reasonable size constraints in many applications.
Well, my desire is first and foremost reliability and getting ahead of a ticking time bomb. I don’t want to have to do anything other than replace in kind if I don’t have to, but if something is “better” and is a drop-in replacement without adding chokes or resistors, then why not.
The caps in question are the big ones and little black ones. I think the ones on the left side are easy pickings too. Not sure if the brown ones on the bottom are needed for PS reliability but while I’m in there...
E3048BE0-9581-4C8B-B62F-FE24D6582486.jpeg
 
...also those rectifiers need to go too but I have no clue what a “diode bridge” is and resistors apparently have to go in with them and voltage needs to be monitored...it makes my head spin.
 
So would there be a benefit to using film in power supplies? I’ve heard people say that since it’s not in the Audio path and just doing the heavy lifting of the power supply, “good sounding” caps don’t matter there.

I think the final capacitors in the power supply are very much "in the audio path." I am not one to argue for boutique capacitors, or any nonsense like that, but I think one definitely should bear in mind that the audio signal passes through those capacitors, and so one needs to make sure, one way or another, that there is no significant audio signal appearing across the power supply capacitors. This is not a subtle thing, particularly; it really just comes down to making sure that across the entire audio frequency spectrum, the power supply should present itself as near enough to a dead short at the audio frequencies that it is not giving any colouration to the musical signal.
 
Well, my desire is first and foremost reliability and getting ahead of a ticking time bomb. I don’t want to have to do anything other than replace in kind if I don’t have to, but if something is “better” and is a drop-in replacement without adding chokes or resistors, then why not.
The caps in question are the big ones and little black ones. I think the ones on the left side are easy pickings too. Not sure if the brown ones on the bottom are needed for PS reliability but while I’m in there...
Actually film caps are more reliable. Most generic electrolytics have a projected lifespan of 2 to 3 thousand hours. Film caps on the other hand are made with non layers of insulator (plastic film) and usually a layer of metallized film. This means there are no chemical component separation which happens in 'lytics. Also film caps like Solen are self healing. If an arc occurs the area that was affected will heal itself with the melted plastic. Thus film caps have the possibility of having an unlimited lifespan far outlasting the builder of the unit.
Film caps also perform better than 'lytics, in all the important categories except size. This is probably why they can be a sonic improvement. In a preamp the power supply is usually of smaller values and film caps can be easier to implement.
Solen is not the only type available for power supplies. Panasonic and Vishay make a DC Link cap which is in a box shape. They are physically smaller than Solens and can fit under a thin chassis, although the Fisher chassis is too thin. Anyway if you can fit them in or under your chassis i am sure you will not be disappointed.
 
So would there be a benefit to using film in power supplies? I’ve heard people say that since it’s not in the Audio path and just doing the heavy lifting of the power supply, “good sounding” caps don’t matter there. If I’m taking the time to work on these things, I’m not too concerned with saving $25 on the cost...a few hundred in caps is another story if it won’t make an audible difference.

I want to replace the lytics in my MR71’s, of which there are only a few and was wondering what I should buy (most are disc). The big 3 and the can are only power supply and are very easy to get to and have plenty of room around them. The little ones are Audio path and harder to get to. The power supply are the ones I am most concerned about as I don’t want a melt-down and all seems to be “working” fine right now in 55 year old caps.

And film, not poly?
Keep in mind that "the can" is probably three or four caps in one, so replacing it with film caps (which are never multi section) can mean much, much more real estate. Having said that, DC Link film caps are rectangular and more efficient with space than the older rounded types so it may be possible to figure it out.
 
Actually film caps are more reliable. Most generic electrolytics have a projected lifespan of 2 to 3 thousand hours. ...

Well...yes, 2000-3000 hours, but at full rated temp and full rated ripple. Reductions in either greatly increase the life. After all, look at how long the original caps have lasted in so many units.

The electros I selected for my current tube amp project, while carrying 105C and 2000 hour rating, max out the Nichicon application life calculator at 15 years. All but certainly they'll last longer but the calculator just deadhead at 15 years. Again, the evidence all around us in gear where the majority of electros last way more than 2000-3000 hours.

That is not to say film caps might not last even longer, but the 2000-3000 hours mentioned for electros will be exceeded many times over in most applications.
 
I think the final capacitors in the power supply are very much "in the audio path." I am not one to argue for boutique capacitors, or any nonsense like that, but I think one definitely should bear in mind that the audio signal passes through those capacitors, and so one needs to make sure, one way or another, that there is no significant audio signal appearing across the power supply capacitors. This is not a subtle thing, particularly; it really just comes down to making sure that across the entire audio frequency spectrum, the power supply should present itself as near enough to a dead short at the audio frequencies that it is not giving any colouration to the musical signal.
But didn't you just make the argument that "the power supply should present itself as near enough to a dead short at the audio frequencies that it is not giving any colouration to the musical signal". Then electros. should do exactly the same thing as a film cap, bypass the signal to ground in the power supply. IMO, the power supply caps can only affect the sound if they are being used too hard and can't suppress enough PSU ripple frequency.
 
Well, my desire is first and foremost reliability and getting ahead of a ticking time bomb. I don’t want to have to do anything other than replace in kind if I don’t have to, but if something is “better” and is a drop-in replacement without adding chokes or resistors, then why not.
The caps in question are the big ones and little black ones. I think the ones on the left side are easy pickings too. Not sure if the brown ones on the bottom are needed for PS reliability but while I’m in there...
View attachment 1160148

If you want something more than a general discussion of whether film caps can be used to replace electrolytics, it would help if you'd tell us:

- what type of gear is this? Brand? Model? Post a schematic if possible.
- what is the value (uF) and the voltage rating of the cap(s) you want to replace?
- how deep is the chassis?

I used some one of the Panasonic film caps like this one when I rebuilt a Fisher SA-16 console amp a while back:
https://www.digikey.com/product-det...ic-components/EZP-E50356MTA/P15860-ND/3837582

They make various values and voltages so physical sizes vary - check the sizes for the value you need. I used this one as the first cap in the PS in the Fisher and it fit fine. It's less than an inch deep.

...also those rectifiers need to go too but I have no clue what a “diode bridge” is and resistors apparently have to go in with them and voltage needs to be monitored...it makes my head spin.

A diode bridge is just four diodes . . . diode bridge
 
You would be best off sending your MR71 to a RF expert like Terry DeWick and allow him to do a complete work over on it including a complete alignment.

Just as a note maybe the least reliable part in your tuner is the photo resistor which uses a light bulb unlike today's which use a LED. That and frozen tuning slugs.......
 
Back
Top Bottom