• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

having problems finding capacitors for first re-cap

That's cheating!

Using manufacturers guidelines is clearly cheating!

Seriously, thanks for posting that link.

Don't get me wrong guys, you should always rebuild your amp in a way that makes you feel good about it.

I mean, what fun is a hobby you don't feel good about?

If that means cutting the original capacitor open and hiding the new one inside, I'll bet it looks sweet.

I did try some of the Russian PIO caps on my last repair, but, I sent the thing off to my buddy after a short checkout so i have no clue if it was great now or what :)

But I bet he likes it just because he knows he has those caps in it now.

Keep us updated on your flying wedge amp.

Dan
 
Fred Longworth said:
It is not true that you can go up in voltage on an electrolytic capacitor without at the same time altering the performance of the circuit.

Let me put this another way. You have some latitude as far as increasing the voltage, but nowhere near as much latitude as is commonly discussed on the Web.

Here's a thought experiment. You are replacing a 100uF/10v capacitor used in the regulator section of a power supply board on a late-seventies Pioneer receiver. You are having trouble finding the correct value, so you use a readily-available 100uF/50v device. Nearby, there's a 220uF/16v part, which you replace with a 220uF/50v cap. In fact you replace eight parts with devices that have voltage ratings from 3 to 5 times as high as the originals.

Then you turn the equipment on, and you find that the power supply isn't working quite as you had hoped. For one thing, every now and then one of the regulator transistors oscillates!!! This phenomenon comes and goes.

Why is this happening? Here's why. When you hit an electrolytic capacitor with a polarizing voltage, the electrolyte forms. If you hit it with a polarizing voltage considerably lower than it was designed to sustain, it will often not fully form, and so the capacitor -- especially if it is used for power supply applications -- will not function at the extremely low-impedance state that you are hoping for.

This characteristic does not afflict film caps, just electrolytics. For this reason, on major power supply recaps, I strongly prefer devices with voltages ratings at, or only slightly above, the original values.

Fred
Click to expand...


Thanks, Fred, for contributing more to my detailed understanding of solid state electronics. Great descriptive post.
 
Hmmm..... Makes you wonder why capacitor manufacturers continue to make electrolytics in a wide range of voltages, for example, for SS use 6.3, 10, 16, 25, 35, 50, 63, 80, 100. Gives considerable creedence to Fred's excellent post.

If the voltage rating doesn't matter why not 2 or 3 voltage ratings for all electrolytic capacitors, and only that many to cover for possible size issues. :scratch2:

Just wondering....

John
 
Hyperion said:
Hmmm..... Makes you wonder why capacitor manufacturers continue to make electrolytics in a wide range of voltages, for example, for SS use 6.3, 10, 16, 25, 35, 50, 63, 80, 100. Gives considerable creedence to Fred's excellent post...Just wondering....

John
Click to expand...

Well, it seems we really need a manufacturer expert to give us the full story. There was a lot of good input and food for thought in Fred's post.

I'm not sure but, FWIW, I thought I read elsewhere a website that echoed information similar to what Fred had posted and that something in the order of up to +35% capacitor working voltage for electrolytics was probably a reasonable figure to work within - but that's just going from memory, so no back-up on it or the source credentials.
Hyperion said:
Hmmm.....If the voltage rating doesn't matter why not 2 or 3 voltage ratings for all electrolytic capacitors, and only that many to cover for possible size issues. :scratch2:

Just wondering....

John
Click to expand...
Good question and I'd certainly like to know. I would imagine there are cost, size, weight, application, optimum performance, parameter compromises, and other trades. Just because you can substitute (see further comment below) a higher voltage cap for a lower one doesn't mean it's an optimum or equivalent choice, or without compromises. High voltage caps are much larger than low voltage, more material, maybe different construction, maybe different electrolytes etc. While size and weight might not be big factors for something like tube amp power supplies, many SS applications are space or weight critical. Also, please note that that guide in the link did not say that the substitution was acceptable or advisable for all conditions.

The CDE guideline link was for actual manufacturer information, to show that substitution is allowed (for CDE's products anyway) - but within the guidelines of the other parameters, i.e. ESR and Dissipation Factor (DF) (so not under any and all circumstances). That would indicate there's some homework to be done, not just blindly replacing. You could take the view that, considering that DF is the ratio of the ESR to the capacitive reactance, the guide can add further credence to Fred's post, in that if you do not stay within those given guidelines you can affect the equivalent R & Xc of the original capacitor in the circuit, and hence the performance of the circuit.

It seems the safe approach is to stay at or moderately above the original working voltage ratings as many have recommended...or do your homework.

Sorry no answers but maybe helps the wondering a little.:scratch2:
 
Interestingly enough

Right, cost and size are the big ones.

You can buy the same uf and voltage rated cap and still not have the same ESR etc . . . So there is some more stuff to be paranoid about.

uf

voltage

ESR

DF

polarized or not

Material used

size


This is why the subject is so deep and subject to so many opinions.

And then there are the people who feel the mfg does not properly form the caps . . .

It is amazing we can ever fix anything!

Dan :banana::banana:
 
Fred Longworth said:
It is not true that you can go up in voltage on an electrolytic capacitor without at the same time altering the performance of the circuit.

Let me put this another way. You have some latitude as far as increasing the voltage, but nowhere near as much latitude as is commonly discussed on the Web.

Here's a thought experiment. You are replacing a 100uF/10v capacitor used in the regulator section of a power supply board on a late-seventies Pioneer receiver. You are having trouble finding the correct value, so you use a readily-available 100uF/50v device. Nearby, there's a 220uF/16v part, which you replace with a 220uF/50v cap. In fact you replace eight parts with devices that have voltage ratings from 3 to 5 times as high as the originals.

Then you turn the equipment on, and you find that the power supply isn't working quite as you had hoped. For one thing, every now and then one of the regulator transistors oscillates!!! This phenomenon comes and goes.

Why is this happening? Here's why. When you hit an electrolytic capacitor with a polarizing voltage, the electrolyte forms. If you hit it with a polarizing voltage considerably lower than it was designed to sustain, it will often not fully form, and so the capacitor -- especially if it is used for power supply applications -- will not function at the extremely low-impedance state that you are hoping for.

This characteristic does not afflict film caps, just electrolytics. For this reason, on major power supply recaps, I strongly prefer devices with voltages ratings at, or only slightly above, the original values.

Fred
Click to expand...

Excellent information Fred ! Always learning from guys like you who know their stuff !
 
....So what is a safe parameter to increase the voltage within? 35% has been mentioned, would 50% be too much? I have some 50v caps I picked up to replace the 25v cap in the unit thinking that I'm ok, hmmmm...
 
Depending on the location it may not matter... however if it was me I would go up one 'click' only on voltage - so, for a 25v cap = 35v max replacement.

See what others say on the subject - there are bound to be more replies on this...

Just my 3 ha'pence worth

John
 
You must log in or register to reply here.
Back
Top Bottom