1974 Sliverface Vibro Champ with death cap

[punkykatt]

Hello all, got a 1974 Silverface Vibro Champ on the bench in for a check up.  It looks like a factory installed 3 conductor grounding power cord and it still has the .047 death cap from the fuse holder to ground.  This amp appears to be virgin stock.  I thought when the 3 conductor cord was installed you are to remove the death cap???  Did Fender make a mistake?
Thanks. Punky

[AZJimC]

No, Fender did that, same in my 72 Super, and 75 Bassman, just get rid of it,, and hook up like normal. It's there as a ground shift/lift... center click lifts the neutral/hot grounding, leaving just the safety ground. The cap allows you to shift AC ground on the amp

[PRR]

In 1974, 3-pin outlets were not everywhere. If you can't use the 3rd pin, you will get a buzz, unless you tie the chassis to the line with a capacitor.

This amp will work low-buzz either way.

But 40 years later, you SHOULD have 3-hole outlets everywhere you play. (Though I have seen a lot of 3-holers where the 3rd hole wasn't connected to anything...) Since those caps DO fail in old age, often SHORT, I would incline to re-wiring to "modern" style, no cap.

[sluckey]

Back in the days of two prong power cords and ungrounded wall outlets, the line filter cap (often called death caps) actually could be a hazard. But I have a different view of modern line filter caps . When you use a properly wired three prong power cord and it's plugged into a properly grounded wall outlet, the term "death cap" is no longer applicable. The cap should have a 'CLASS Y' rating. Fender used a cap that was rated "U.L. .047µF 600V ". Was this the same as today's CLASS Y rating? I don't know.

Lots of high quality test equipment, computers, and other consumer electronics use a IEC line filter with a cap across the line (CLASS X) and two caps from either line to ground (CLASS Y). Most all industrial and military equipment use line filters of some kind, many that are pretty elaborate and expensive. This line filter is an improvement over the single cap line filter and serves the same purpose. Should they be called death caps and removed from the circuit? I don't think so.

Here's a link to some good, easy to read info about line filters. You may change your thinking about the "death cap".

     http://www.justradios.com/safetytips.html

And here's a pic of a high quality IEC line filter. This one is in my AC-15. See the "death caps" inside it?

[John]

Hmmm. I get a vibrato-like pulse in my amp when the ceiling fan is turned on. Not bad, but noticeable. I wonder if those caps would fix that?

[Fresh_Start]

Sluckey -

Is this part similar to what's in your AC-15?
http://www.mouser.com/ProductDetail/Schaffner/FN9222EU-3-06/?qs=sGAEpiMZZMv1TUPJeFpwbo3VfjMofYIpdl6Lmp%252bBPAs%3d

I'm a little confused by the attached schematic. It shows two grounds. Is one the safety ground and the other the chassis of the amp/radio?  Or is the second ground the circuit ground. I assume that the chassis must always be connected to the earth ground (3rd prong).

Thanks,
Chip

[vibrolax]

Back in the days of two prong power cords and ungrounded wall outlets, the line filter cap (often called death caps) actually could be a hazard. But I have a different view of modern line filter caps . When you use a properly wired three prong power cord and it's plugged into a properly grounded wall outlet, the term "death cap" is no longer applicable. The cap should have a 'CLASS Y' rating. Fender used a cap that was rated "U.L. .047µF 600V ". Was this the same as today's CLASS Y rating? I don't know.

I haven't looked up the details of Class X and Y ratings, but I believe one significant factor is their failure characteristics.  When they fail, they are supposed to fail "safe" in a way that doesn't hazard persons coming in contact with the chassis.  That's what makes proper line filter modules not equivalent to death caps.

Here is something to read:
http://powerblog.vicorpower.com/2013/06/what-are-y-capacitors/

[g-man]

Deleted

[sluckey]

Is this part similar to what's in your AC-15?

Yes. Except my filter has a straight wire connection between the input ground pin and the output ground lug. The one in your link shows a third inductor between the two grounds. I don't really like that idea.

I'm a little confused by the attached schematic. It shows two grounds.

The two grounds are connected together inside the IEC socket.

[Willabe]

Fender used a cap that was rated "U.L. .047µF 600V ". Was this the same as today's CLASS Y rating? I don't know.

I was looking for Punkykatt's schemo yesterday and noticed that on a few Fender schemos, they did have a 3 wire power cord with a cap to ground, no polarity/ground switch.

But on the schemo there's a note for the cap to ground that says 'No Substitute'. So I think it was a special type of construction cap?

Look at this schemo;

http://el34world.com/charts/Schematics/files/fender/Fender_champ_super.pdf

Marshall did use, on a few amps, PT secondary line to CT caps;

http://el34world.com/charts/Schematics/files/marshall/Marshall_major_1967u_lead_200w.pdf

[punkykatt]

Thanks for all the info Guys.  Last month I took in three mid 60`s Ampegs that the owner had a tech previously install the 3 conductor grounding cords. When I plugged them in, each one of them immediately tripped the GFCI`s in my shop. Sure enough each still had the cap to ground in the circuit. They were leaking just enough to trip the GFCI. I clipped them out and all was well. 

I will have to contact the owner of the Vibro Champ to see if he wants to keep the amp 100% stock.

[Willabe]

When I plugged them in, each one of them immediately tripped the GFCI`s in my shop. Sure enough each still had the cap to ground in the circuit. They were leaking just enough to trip the GFCI. I clipped them out and all was well.

Interesting.

I will have to contact the owner of the Vibro Champ to see if he wants to keep the amp 100% stock.

I think that if I where to work on someones amp, that once I did, I would not return it with that cap. Not only for the amp owners safety but but for my safety too, legal safety.


                  Brad       

[Willabe]

One problem is that it may not fit in a chassis that is already drilled for a regular IEC and is too crowded around the IEC.

They also make them in little metal boxes that are soldered closed/sealed for a metal shield. Corcom makes them (encapsulated filter/integrated filter) as do others, Mouser and DigiKey sell them. (I have 1 here and would post a pic but I can't find it right now.)

They come with different circuits and can be very pricey. I think most of them are over kill for a filter for a guitar amp but might be needed for sensitive medical, industrial and military equipment. I can't figure out how to interpret the data for them, frequencies that they aim for from the spec sheets. 

Kevin O'Connor's TUT 5, 20th chapter, is called 'Symmetric Source' and he talks a little about these line filters and shows how to make your own choke, 1 to 2w R flame proof, no value because you wind #16 enameled wire tight over the body and solder the wires ends to the R ends, so the R is shorted and used as a bobbin.     

Or, he lists Miller coil #5219 for the small choke used with the X/Y type caps to make your own filter. (Although he doesn't mention X/Y type caps.)

(The symmetric source is a stand alone power source that is made with a toroidal step down PT. The PT's secondary has a CT so you get 60-0-60acv to cancel some of the common mode line noise. Then he adds a line filter on the PT secondary to "add a bit of RF noise suppression to further quiet our equipment." HBP, when this was brought up before, posted a link showing how to build the same type of power/filter source. So it's out there on line, from a different author.)

Does anyone know if there is a high quality power strip with this built in? I THINK, you could then use it with any amp and get the same protection?

I think the higher end/more expensive models do, like Isobar, but I think the symmetric source would be better? OTOH, we've been playing without these things for many decades. And if you build or rebuild an amp with good lead dress and a good grounding schem your already way a head. But if you need the amp as quiet as possible, because your in a recording studio, then you have a few more options.     

I think some recording studios already use a centered taped secondary toroidal step down PT installed right in a wall circuit breaker panel box that feeds the studio wall outlets.                     

[punkykatt]

"I think that if I where to work on someones amp, that once I did, I would not return it with that cap. Not only for the amp owners safety but but for my safety too, legal safety."


                   
Agreed, out it comes.  What was I thinking!!!!!!!
Thanks

[Willabe]

You wanted to make the customer happy.   

But you know more than he does. And if something were to happen, who knows if they would/could come after you?

Besides it's a SF not even a BF, brown face or old tweed. If a guy's a collector and has an absolute pristine vintage amp AND he's never going to play it, then maybe.

I do worry to much sometimes, but still, think of a classic car, wouldn't you at least redo the brakes and replace the tires if you were going to drive it? 

                 
                            Brad       

[PRR]

> The cap should have a 'CLASS Y' rating. Fender used a cap that was rated "U.L. .047µF 600V". Was this the same as today's CLASS Y rating? I don't know.

My understanding agrees with vibrolax. A golden-age 600V cap was a pretty tough thing, but Y and X caps are tested different, with high spikes, and must fail Open not Short.

No objection to a modern Y cap, but since the chassis is bonded to the 3rd pin, I don't see any use for it.

(Unless you have nasty digital in the box or in the venue. Then caps all over the power inlet, as on Chip's diagram, may partially fire-wall the crap in or out. That's why you see such caps and full filters on modern amps.)

[Fresh_Start]

Are the "Y" caps polarized and the "X" caps not?

The Y caps are specifically designed to fail open AFAICT.

Seems like a single cap in the C1 location of the diagram I posted above would filter out at least some power line noise, possibly at less cost ($8-12 for those IEC boxes). If PRR says the C2 caps are a bit redundant, then perhaps just C1 would do the job. But I'd rather have it fail open and just not filter rather than relying on my circuit breaker or a GFI outlet.

Cheers,
Chip

[sluckey]

Are the "Y" caps polarized and the "X" caps not?

Neither are polarized. Y caps are tougher than X caps and can be used to replace an X cap. Supposedly they are also more expensive than X caps.

Is this part similar to what's in your AC-15?

Yes. All the ones that I have, two grounds are connected together and also soldered to the metal shell. These filters have a current rating so take that into consideration. You would not want to use a 3A filter on a device that draws 5A.

[Bill McKenna]

Interesting post.. much more than I ever knew about death caps. have been removing them for years :(

If I were to want to put a Death cap back into an amp with modern 3 prong, for this possible need where ground was missing what would be a good candidate. 600Vdc Orange Drop maybe?
Suppose it can't hurt to have a cap there based on the previous posts.

thx
Bill

[sluckey]

for this possible need where ground was missing

What does that mean?

You should only use a Class Y cap. I don't think orange drops are class Y.

[John]

for this possible need where ground was missing

For when the guitar player uses a 2 prong adaptor (in his back lawn with the dew on the grass to an outside ancient outlet that's probably wired backwards)

[John]

So anyway, been giving this more thought. Would it actually then, be good practice to install a Class Y cap between the neutral/white wire and the earth ground terminal?


If so, I think I myself would be inclined to do so for any amp that would be used by a gigging musician since like youall say, clubs are notorious for not having correct/safe wiring.

[sluckey]

I've never put them in any of my builds. And I only have one amp that I used that EIC filter. I have one more line filter that may go into another amp one of these days.

My main point to all my discussion is that the term "death cap" is kinda meaningless once the amp gets a 3 prong power cord that has the green safety wire connected to the amp's chassis. Still requires the house wiring to be properly grounded to be safe.

If you use one people may call you stupid and you'll have to have this long conversation, and they will likely still call you stupid. Many of these same people would not hesitate to use an EIC line filter but would cry loudly at the thought of a death cap.   

[John]

Oh my, I'd never install a death cap!!

[Fresh_Start]

Oh my, I'd never install a death cap!!

Sluckey's point is that the switchable cap to chassis ground for either what SHOULD be hot or what should be neutral doesn't have the same evil potential (pun intended) once the third ground lug is also attached to the chassis as shown in this schematic:

http://el34world.com/charts/Schematics/files/fender/fender_deluxereverb_a1172.pdf

(Posted mostly because I wanted to understand what was being said, so I found this schematic)

Cheers,
Chip

[John]

Sorry, I should have put the    in there. :-) I'm in retail, so I'm all too familiar with the power of perception.


Thanks for posting that schematic. Actually, I think it's something I might do if another guy wants one built. Or at least give them the option. My buddy I built one for had the dewy grass/2 prong adaptor/outside ancient outlet/holy shit that hurt!! thing happen. If they had to use the adapter to play a gig, it would add a little safety (if I'm thinking right).


Of course, I've already built my 2 for this year. 

[Fresh_Start]

My buddy borrowed an all original 1963 Princeton Reverb.  The electrician who wired his house had whatever the opposite of OCD is - for any given outlet there was no telling which setting of the Ground switch might give you a buzz through the strings. 

I ended up removing the "death cap" and installing a 3-prong plug for the amp's actual owner but wish I'd known about this approach at the time.  There's no way for the chassis (or input jack ring) to be "hot" and the amp's owner would've been happier with the concept of keeping the circuit "closer" to the original. 

Of course 2 "Y" caps in place of the "death cap" and Ground switch would've been even better.

Chip

[John]

The more I think about it, I'll call Chris and say "hey buddy, I need to install a death cap in your amp." 

[PRR]

Get paid in advance.

[sluckey]

I fear I've opened Pandora's box!

[shooter]

the opposite of OCD

ADD, when they say opposites attract, don't believe it otherwise you might have

opened Pandora's box

[dude]

Hmmm. I get a vibrato-like pulse in my amp when the ceiling fan is turned on. Not bad, but noticeable. I wonder if those caps would fix that?

HA, that's the sound waves bouncing around from the fan....

[Willabe]

I fear I've opened Pandora's box!

Big framing hammer and 16d nails will close it back up!     

If any one reads the whole thread AND the links, it's pretty clear, make sure you have a Solidly bonded ground/3rd wire (to the chassis) but if you opt to use line to ground cap(s) Use Y2 class caps not poly prop./plastic caps.

[Ed_Chambley]

I fear I've opened Pandora's box!

I don't this is so.  I have 2 collectable amps that still have the 2 prong cords.  I did not want to change them since both are exactly as they were purchased.  What you did is remove my concern as I checked both and the caps are still good.  These do not leave the house so I do not have concerns with polarity.

Even with my 3 prong amps I still carry AC outlet ground tester when I go somewhere with any of my amps.  I keep one in my bag with other items such as strings, tubes, fuses.....etc.

Great topic.

[xm52]

As was said, most amps with three conductor power cords don't have a line filter cap. From a regulatory standpoint, they are more trouble for the manufacturer than they are worth. It costs more to do the additional testing when going through the certification process.

I suppose that an advantage of the line filter cap is that it helps remove high frequency line noise. Not something you want inside your amp.


Some companies such as Ampeg still use these caps even though they have three conductor power cords. They use a three position polarity switch, the center position removes the cap from the circuit, the outside positions switch the cap to either the line or neutral. There is also a cap between line and neutral.

[Fresh_Start]

Ignorant question:  if the polarity of an outlet is reversed, how does a small value (.0033 uf) capacity help?  It's a short circuit to ground for high frequencies but an open circuit for lower frequncies (say 60Hz) isn't it?

As was said, most amps with three conductor power cords don't have a line filter cap. From a regulatory standpoint, they are more trouble for the manufacturer than they are worth. It costs more to do the additional testing when going through the certification process.

I suppose that an advantage of the line filter cap is that it helps remove high frequency line noise. Not something you want inside your amp.

Some companies such as Ampeg still use these caps even though they have three conductor power cords. They use a three position polarity switch, the center position removes the cap from the circuit, the outside positions switch the cap to either the line or neutral. There is also a cap between line and neutral.

I don't understand why Ampeg's switch is preferable to the circuit I posted in #5 minus the inductors. IOW could the switch cost less than a Y capacitor?  Or is the middle open beneficial in some circumstances?  I can't think of one.

Respectfully,
Chip

[xm52]

The purpose of the polarity switch is to remove high frequency interference. The inductance of the transformer and the type Y capacitors that they use sets the frequency of the low pass noise filter. Typically the capacitance values found in amps are low. As you said, you want to shunt the high frequency differential and common mode noise to ground. The values used in their design work. It's such a simple circuit but the math behind it isn't, as seen in some papers. The reflected impedance onto the high voltage side of the power transformer is important so what they put on the primary side is of concern.

The middle position of the switch is the equivalent of no filtering. That is where I leave amps that have a three position switch. The power in my area is pretty clean and I usually don't find a difference in the three switch settings. Some clubs have some pretty flakey wiring/lighting and having the circuit does make a difference.

A Type Y capacitors are relatively inexpensive. They can cost under a $1 and up. Regulatory standards are pretty strict and costly to adhere to. A manufacturer needs their products to conform everywhere that they sell them. North American regulatory agancies, Europe, Japan, and other regions all have demanding requirements when it comes to the primary side of the power transformer. The regulatory agency requirements affect design decisions.

Well designed amps will have some level of protection against spikes and noise.  Not every company offers the same level of protection. In the case of this design, the vintage models had a polarity switch. They may have decided to keep the same function in the reissue for historical reasons which is why that circuit is there. As you pointed out, better, and more costly options are available.

Here is a link that may be of interest. Note the differential and common mode noise sections.

http://www.schurter.com/content/download/339606/11198618/EMC+for+Dummies_e-News+Final+3.27.2015.pdf#page16.webloc

[PRR]

> Here is a link

Notes on X caps:

___________________________________________
"X capacitors are self-healing(SH) metalized paper or polyester types. As a result, these self-healing capacitors can withstand a high potential surge pulse. The capacitor can lose some of its capacitance, but the insulation remains the same."

Safety class:
X1 4kV pulse 1.2/50µs
X2 2.5kV pulse 1.2/50µs

High potential test:  L–N:
Engineering test 2121VDC; 60s 
Production test 1075VDC; 2s
________________________________________

The "600V Orange Drop" might survive the 1075V production test, but not 2KV.

The metalized ODs might burn-open but this is not tested. There are also bigger Foil caps which will not burn open in an arc (one case where bigger is not better).

[xm52]

A lot of techs use orange drops in the polarity circuit. It's a lot easier.


One of the problems with type X and Y safety caps is that they often have short leads that are intended for circuit board mounting. Finding the value and voltage specs that you want with long leads is often difficult. I find that making a PCB to hold the part is often easier.


A good reason why so many opt to remove the polarity circuit altogether. The gain is not worth it and if you want this type of power line filtering and spike protection, it is available in some power strips.


Regulatory agencies insist on safety caps in polarity circuits. If I'm keeping this circuit in an amp, I like to use safety caps in an attempt to conform to current requirements.


Although there are amps on the market such as the SVT's that have polarity circuits, these tend to be older designs. Most newly designed musical instrument amps that I can think of, do not have polarity circuits.