Capacitor Replacement Advice

[hossymandias]

Hello sages, I am embarking upon a recap of my old National Model 90 and I need some advice. Unless I get advice to the contrary, I plan on replacing all electrolytics (including cans) and all paper caps in the amp. I ordered audio-grade orange drops and film from Mammoth to replace the papers, but I'm stuck on the electrolytics.

Here's the thing: without thinking I ordered a bunch of bulk 22uf and 10uf 400v electrolytics from Amazon. They are sold by Amico, but are marked JH and Chang-X respectively.

Here's the link

I received them yesterday, and they look "fine," but I began to worry about the quality. I researched a bit on the web, but I can't find a definitive answer to this question:

How much do I need to worry about the quality of caps when it comes to electrolytics?

At first I think, well most of them aren't attached to the audio line, so it's no big deal...but then again, they are filtering the power supply, so it IS a big deal.

Any advice is appreciated. Feel free to say "of course it matters, dummy," although I hope you say, "your caps will be fine."

[Phil_S]

My amateur gut reaction is that the caps you ordered will be more than OK and are probably significantly better in quality than the ones you are replacing (guessing they are really old.)

Notes and possible issues:
-Duty cycle. How much do you use this amp? Do you really need 10,000 hour rated caps? These are likely 2,000 or more hours. Good enough even for a gigging musician who play 6 nights a week for 4 hours. At that pace, a 2,000 hour cap will go close to 2 years.
-Voltage. Those are 400V rated. As long as your B+ power ladder never goes over that, those caps are fine. You don't want them stressed out by voltage overload. If you need 450V rated, or 500V rated, then you have the wrong caps.
-Capacitance tolerance rating. Old caps maybe have been rated as much as +50%/-20%. The new ones are going to be much closer to spec.
-Physical size. These are likely to be considerably smaller. Let's hope that doesn't create some unexpected challenge in mounting them.
-ESR rating. These cheap caps probably don't compare favorably to brand name caps, but they are still way better than what you are replacing. Don't get snookered here.
-Don't use 400V rated caps for cathode by-pass. Get the right 25V or 50V caps.
-20u-22u-25u or 8u-10u are considered reasonably equivalent. Don't sweat this small detail if it crossed your mind.
-If this amp has a tube rectifier, make sure the first node filtering doesn't exceed the spec for the tube.

One real problem people have been dealing with over the years are counterfeit caps. They stuff a radial inside an axial case and the paper outside does not indicate the real cap inside. Pacific rim countries have participated in this evil undertaking. I'm meter the caps to be sure.

[hossymandias]

Thanks, Phil_S!

This is what I was hoping for! I felt very reluctant to buy $15 capacitors from a specialty supplier for power filtering. The ones I am replacing are indeed very old, and although the ratings are a little off (22mf for 20mf, etc.) I'm aware that amps are easy-to-please in this way, and I did match the V-rating exactly.

Is there a way for me to verify that I don't have a bad batch of fake Pacific Rim caps without an ESR meter?

Thanks again for the quick, helpful reply!

[Blackburn]

I agree with Phil that the caps you got will likely be better than what you're replacing, but I don't buy anything Chinese if I can help it. Also, you'll want axial caps and not radial, like the ones in your link. Pay a little extra and get some F&Ts (22uf @ 500v) and go with Nichicon for the bypass caps, since there's an assortment of values/voltage ratings to choose from and they're much cheaper than Spragues, and IMO, better. Try Mouser or DigiKey.

[xtian]

Good places to shop for caps for tube amps:

tubesandmore.com
justradios.com
turretboards.com
apexjr.com

[hossymandias]

Thanks guys.

Blackburn, I actually bought the radial electrolytics to replace the 20-10-10 cans. I'm planning on disconnecting the cans but leaving them on the chassis for looks, and wiring in the replacements under the chassis. Is there a difference I'm unaware of between radial/axial besides the physical placement of leads?

Besides the can replacements, everything is Vikiin Orange Drop, Vikiin Polyester, or Nichicon electrolytic. I only went to China for the can replacements!

What do you think?

[xtian]

Is there a difference I'm unaware of between radial/axial besides the physical placement of leads?

No, but you can find radial much cheaper, in general, because they're used far more often for PCB mounting. I've been finding creative ways to use radial caps in my turret board layouts.

[Paultergeist]

-Don't use 400V rated caps for cathode by-pass. Get the right 25V or 50V caps.
.....

Phil,
I am curious about this recommendation. I had always thought that having a voltage rating in excess of that which was required was just fine (albeit the higher voltage-rated cap might be larger).

Is there some other consequence of using a high voltage-rated cap for -- say -- cathode by-pass when the voltage experienced at that location will be pretty low?

I confess that -- in the course of my on-going Rocket build -- I was planning on using a 300-volt 220uF cap I happen to have on hand for the power tube cathode by-pass......that's why I ask.......

[Blackburn]

-Don't use 400V rated caps for cathode by-pass. Get the right 25V or 50V caps.
.....

Phil,
I am curious about this recommendation. I had always thought that having a voltage rating in excess of that which was required was just fine (albeit the higher voltage-rated cap might be larger).

Is there some other consequence of using a high voltage-rated cap for -- say -- cathode by-pass when the voltage experienced at that location will be pretty low?

I confess that -- in the course of my on-going Rocket build -- I was planning on using a 300-volt 220uF cap I happen to have on hand for the power tube cathode by-pass......that's why I ask.......

Will work fine, just a waste of a good high voltage lytic. I can't imagine why you'd prefer a cap that's probably ten times larger than one rated at a much lower voltage and likely much, much cheaper.

[Phil_S]

Just thinking along the lines of using the right tool for a job. Don't drive a carpet tack with a sledge hammer. Sure, you can do it if you want to, but why would you when you can easily get a tack hammer. I see using a 400V cap where you need a 25V cap as bad practice.

Also, somewhere in the recess of my memory, I recall (maybe erroneously) that someone somewhere provided a good technical justification.

[Phil_S]

Is there a way for me to verify that I don't have a bad batch of fake Pacific Rim caps without an ESR meter?

Yes, but do you really want to go to this much effort?
http://geoffg.net/Measuring_ESR.html
http://paulorenato.com/joomla/index.php ... s&Itemid=4
OTOH, this is something you might consider:
http://www.flippers.com/captest244.html

Really, though, if you have a DMM with a cap checking function, that is certainly a reasonable thing to do.

[Paultergeist]

Will work fine, just a waste of a good high voltage lytic. I can't imagine why you'd prefer a cap that's probably ten times larger than one rated at a much lower voltage and likely much, much cheaper.

Good to know. Ironically, the big 300-volt (rated) cap is going to be the cheap option if for no other reason than I bought one long ago. A couple of years ago, I bought F&T caps for this (Rocket-inspired) build. Ignorance being bliss, I was not sure at the time about the voltage requirements at the cathode by-pass position, so I ordered the 300-volt (rated) F&T 220 uF axial cap. (Better safe than sorry?) When I saw the thing, it was absolutely huge, but I figured maybe I can just barely fit it in there.....otherwise, I'll have to buy somethings else.

Thanks for the replies.

[Blackburn]

http://www.mouser.com/ProductDetail/Nic ... W4UNJbM%3d

I'd add a few other things to an order to justify the shipping.

[sepulkrisiun]

Hello I'm picking up pieces of an amplifier Philips 50's, and he had big black capacitors 0.1uf and 0.02uf and in perfect condition, I'm thinking of putting them in place of the current oragne drops in my JTM45, what do you think? I wanted a more vintage sound.

I also have some carbon resistors that no longer has the original value, but still has a resistance, I can use them anyway?

I also have capacitors that over the years lost capacitance, it is safe to use them since the value is suitable to my circuit?

sorry for my English, because I live in Brazil and I'm still learning the language.

[armillary]

Olá sepulkrisiun. Please do not use capacitors or resistors from an old amp to try to make a new amp sound vintage. Old capacitors are likely to fail and cause expensive damage to your JTM45. The capacitors you mention are called "black beauties" and are normally replaced by amp restorers with modern capacitors of the correct value. There's lots of good information on why you should not reuse old caps here:
http://www.justradios.com/captips.html

My advice for getting more vintage tone from your JTM45 is to find the right vintage pedal. Clones of vintage pedals are almost as good as the original ones and cost much less. You can build your own Dallas Arbiter Fuzzface clone from a kit if you like. I also suggest the Proco Rat, for a vintage tone from a modern pedal.