# when replacing filter caps......cans or separates?



## Lincoln (Jun 2, 2008)

when replacing the "can" style filter caps on old amps........is it more desirable to find matching value capacitor cans or is it better to build a little capacitor board and mount separates to it inside the chassis somewhere & wire them in?

Aside from trying to make it look as original as possible, does the amp really care?

The old can could even stay in place for "looks", right? ground all the terminals?


----------



## greco (Jul 15, 2007)

Lincoln said:


> when replacing the "can" style filter caps on old amps........is it more desirable to find matching value capacitor cans or is it better to build a little capacitor board and mount separates to it inside the chassis somewhere & wire them in?
> 
> Aside from trying to make it look as original as possible, does the amp really care?
> 
> The old can could even stay in place for "looks", right? ground all the terminals?


In order to test my skills in the area of electronics, I'm going to make some guesses here.

I think it would be desirable to find the matching value of capacitor "cans" only because I think it would be an easier fix. If you were to build "a little cap board" you might (possibly) run into issues regarding wires/wire dressing from the cap board, along with having to find the space and a method of securing it well to the chassis or whatever.

Does the amp care....I doubt it, given that you have matched the specs of the original "can" caps. Certainly you should be able to leave the old cap "cans" in place. I would think that just disconnecting all of the "can" cap terminals would be suffice.

I await the comments from amp techs. 

Cheers

Dave


----------



## Wild Bill (May 3, 2006)

Lincoln said:


> when replacing the "can" style filter caps on old amps........is it more desirable to find matching value capacitor cans or is it better to build a little capacitor board and mount separates to it inside the chassis somewhere & wire them in?
> 
> Aside from trying to make it look as original as possible, does the amp really care?
> 
> The old can could even stay in place for "looks", right? ground all the terminals?


The amp doesn't know or care, Lincoln!:food-smiley-015:

Finding cans can often be very difficult. The call for them is so low in volume today that there is nowhere near the variety of values and voltage ratings that were available back in the Golden Years, when tubes were the technology of all electronics. That means that the few manufacturers around today concentrate on only a few selections where they expect to see the most sales. A 50/50 mfd at 450-500 vdc is very popular - because of all the Marshalls out there. A 30-30-30 @450 with an extra section of 20 mfd @ 50 vdc would be rare to simply not available.

The good news is that electrolytics are much better made today than years ago and more important, they tend to be a lot smaller! Individual units are easy fit under the chassis. Vendors like thetubestore.com carry axial lead units. This makes things much easier! Instead of using a small board to mount radial lead caps with both leads on the bottom I just drill small holes to mount a tie strip or two. This makes re-capping an old Traynor or even an Ampeg a piece of cake!

If you leave the old cans for appearance sake, don't bother grounding the terminal. If there is nothing connected to them they will do no harm.

Often you will have to "fudge" the value of the replacement cap a bit. Just remember these simple rules. The voltage rating can ALWAYS be higher! That is the safe operating voltage rating and the higher the better!

If you have to use a different value, round up instead of down! That means if the amp used a 68 mfd cap (a value not usually offered any more) just use an 80 mfd or even 100 mfd.

Originally, filter caps were not made that close in value anyway. The usual tolerance was -20%/+80%. With a broad range like that, there is no need to be overly "anal" about a replacement value.

Wild Bill/Busen Amps


----------



## dtsaudio (Apr 15, 2009)

Dave,
You're right the amp doesn't care as long as the new caps are spec'd properly.
Cost could be an issue as is availability. There are some new manufacture can caps, but they're relatively expensive compared to single caps, and may not have enough sections, proper physical size etc
.
It's a bit of judgement call which you use


----------



## greco (Jul 15, 2007)

Wild Bill said:


> The amp doesn't know or care, Lincoln!:food-smiley-015:
> 
> Finding cans can often be very difficult.
> 
> ...





dtsaudio said:


> Dave,
> You're right the amp doesn't care as long as the new caps are spec'd properly.
> 
> Cost could be an issue as is availability. There are some new manufacture can caps, but they're relatively expensive compared to single caps, and may not have enough sections, proper physical size etc
> ...


There we have it... ..availability, cost, etc., etc. .....based on real experience, not my "book learnin'. 

Many thanks for helping me learn more.

At least I got the part correct that the amp won't care...LOL

Cheers

Dave


----------



## FrankyNoTone (Feb 27, 2012)

Lincoln said:


> ...Aside from trying to make it look as original as possible, does the amp really care?...


Yes, it could matter because new caps are better than old ones. In basic terms, you can think of the capacitor as having a resistor connected in series and this limits how effective it is. So with new caps, with less series resistance, you'll have a less hum and sag, which alters the dynamic character of your amp. Whether this would be audible in your situation is unknown.

The early Fender and Marshal designs were unintentionally designed to suck as high fidelity amps but later ones like the Vox were intentional. By the late 60's/70's, they had the suckage refined to an art so its best not to mess around unless you know what you are doing.

I don't know if "bad" caps are available, but it might be worth looking at. On the other hand, if you feel that your amp is a little flabby and has unwanted "ghost" tones, then better filter caps is part of the solution.


----------



## greco (Jul 15, 2007)

FrankyNoTone said:


> Yes, it could matter because new caps are better than old ones.
> 
> So with new caps, you'll have a less hum and sag, which alters the dynamic character of your amp. Whether this would be audible in your situation is unknown.
> 
> ...


No offence intended, but I don't understand this (bolded) sentence. 
If your existing caps were old, but not leaking and/or extremely out of spec, why wouldn't you just leave them...rather than hunting for "bad" caps as replacements?

Maybe I'm missing something here.

Cheers

Dave


----------



## WCGill (Mar 27, 2009)

Antique Electronic Supply


----------



## FrankyNoTone (Feb 27, 2012)

greco said:


> No offence intended, but I don't understand this (bolded) sentence.
> If your existing caps were old, but not leaking and/or extremely out of spec, why wouldn't you just leave them...rather than hunting for "bad" caps as replacements?
> 
> Maybe I'm missing something here.
> ...


Those electrolytic caps age and the (effective) series resistance get worse and worse. Heat is the great enemy and there's lots of heat inside a tube amp. Also, the actual act of filtering the ripple causes the capacitors to heat up because of that series resistance. Back in the day, I actually "popped a cap" because of this effect in a specialized circuit... I was a bit of a mad scientist when I was younger, and I'm so glad I survived the spew of chemicals and random shocks :
Voltage doubler - Wikipedia, the free encyclopedia

Oh, and here's a link to the capacitor resistance thing: Equivalent series resistance - Wikipedia, the free encyclopedia

And now the punch line... power supply hum & sag can be adjusted on Line 6 POD HD amp modelers by turning a dial


----------



## nonreverb (Sep 19, 2006)

Indeed CE/Antique Electronics make the old can type on the original Mallory equipment....they don't come cheap though.



WCGill said:


> Antique Electronic Supply


----------



## Lincoln (Jun 2, 2008)

WCGill said:


> Antique Electronic Supply


Thanks for that link WCGill! I found the pots I've been looking for. :banana:

(Garnet pro 200 with 1M pull bright/pull boost pots)


----------



## greco (Jul 15, 2007)

Any decisions re: the filter caps?

Cheers

Dave


----------



## Lincoln (Jun 2, 2008)

greco said:


> Any decisions re: the filter caps?
> 
> Cheers
> 
> Dave


If I can get new Mallory cans the right value from that antique electronic supply place, I will. I want to order some pots from there anyway. If not, I'll go separate caps. But I'm not going to go separate caps (when new cans are available) just to save $10 or $15. 

Dave2


----------



## jb welder (Sep 14, 2010)

One more thing about the cans, check if/how the casing is grounded. If it has the tabs soldered to the chassis make sure you are equipped to deal with this, you won't do it with a regular solder iron.


----------



## Lincoln (Jun 2, 2008)

what about adding a trim pot style bias adjustment while I'm in there fartin around? Any benifit to it on a simple circuit amp running 2 x 6V6 or 2 x 6L6?


----------

