Univox U-45B: atlas oil .002 (M) DEATH capacitor?

[fatecasino]

I opened my pretty old Univox U-45B and I discoverd a blown element, it looks like a capacitor and it has a printing on it:  atlas oil .002 (M) The strange thing is that it still plays really well even without this element!
Does anyone recognizing it?

[Luke51411]

Looks like a 2nf cap. Do you have a schematic for the amp? I'm sure there is one out there.

[ubersam]

The only 2nF I see is in the mains input, it looks like a chassis grounding safety component. I don't know the proper term for it, a reverse ground lift?.

[thomasha]

wouldn't that be the death cap?

Used to reduce hum, but in case of failure shorted the wall to the chassis?

[tubegeek]

death cap.

To the OP - get out of there - you have no idea what you're doing. Get someone COMPETENT to fix the mains wiring and don't plug it back in until they do.

I'm not kidding!

[fatecasino]

death cap? The one side was indeed connected to a power adaptor and rest of the cap has remain to a wire which goes to the main switch,
I am bit confused a bit now...
I 've been using this amp for ages, with no problem so far. What should I do now?
a.replace this cap? (what capacity?)
b.leave it like this?
c. bin the amp?

I think it's a bit rare to find someone here who repairs these kind of amps

[tubegeek]

Where is "here"?

To expand on my warning, let me explain.

This amp is wired unsafely, using a design that was once common but which is now considered unsafe. Follow the link I posted under "I'm not kidding" - this what killed Keith Relf.

Your question made it clear that you aren't very knowledgeable about working with high voltages. It's not a great idea to learn that on the job, y'know?

There's got to be someone who can fix (update and upgrade) that wiring for you. Any competent tech will add a grounded (3-wire) cord on any old amp that is still wired this way as Job #1 as a matter of course - No competent tech will leave the 2-wire power cord or the death cap as-is.

[fatecasino]

[tubegeek]

Good luck. Have you written a will?

[mth5044]

You don't want to be the path to ground, man.

[fatecasino]

ok, ok, I did some research, things are not so tragic, let's see together some actions:

1. I don't mind about a bit of hum, anyway it worked like this for long time. So I remove totally the death cap.
2. I add a grounded (3-wire) cord, 2 go to the main adapter (220V->110V), the 3rd(ground) goes to chassis?

Is there any additional wiring to be done so this amp will be safe again?

[overdriver999]

I have this same amp,I think mine is same model as yours..I had an electrician from my job install a 3 prong cord for me properly..and mine is filled with those atlas oil caps....tremolo has never worked since I have owned it..think my dad picked it up for me at a yard sale about 25 years ago..give or take a few years..still kickin with all original to me parts other than the updated cord..I hope u get your amp fixed,I want my tremolo working but I ain't pokin around in there..I just have to find an actual amp tech for that.

[slacker]

The guy in that video doesn't understand the problem at all, see the comments section, he thinks the fuse will protect you if mains touches the chassis.

[Mark Hammer]

Once upon a time - and this would be decades back - high-voltage, large-value, electros were freaking huge, required harnesses, and cost an arm and a leg.  So, in that context, "death caps" (for cutie) probably made sense from a production-cost stance.  Besides, NOTHING was properly grounded, and 3-prong plugs on music gear were rare, so it was de rigeur to simply be careful ALL the time, or often enough to remain alive.

In 2015, as "cures" for AC hum go, there are FAR better ways to address it that are not as complicated or expensive as it would have been in 1965.  Use them instead.

[Kipper4]

That guy in the video scares me pointing with his finger inside the amp.
He started off the video with a stick but then, oops.

[ubersam]

wouldn't that be the death cap?

Used to reduce hum, but in case of failure shorted the wall to the chassis?

Ah, so that's the term.

[amptramp]

You can use capacitors across the line or from line to ground but they should be a specific type:

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

Justradios is a parts house operated by Dave Cantelon who is a fellow member of the London Vintage Radio Club.  His site has a lot of good information and complete pricing.  I can vouch for his stuff being good.

[fatecasino]

Hi all! thanks you really much for your advice, I have been studying this issue for the last 48 hours I have increased significantly my knowledge on this topic.

There is though one thing I don't really understand in this discussion here. Since the question is plain, straight and absolutely technical, why do I get all this philosophy talking and opinions which eventually make no sense. In this specific diagram, of this very specific old amp, do you know step by step how to make it a safe amp to use? If not, what's the purpose of all this chatter? I don't really get it.

You speak here about a set of tests that an expert would carry out in order to upgrade this amp. OK, which are these tests? Are they some part of a secret bible and they are not allowed to be described? If you don't know them, there is the option of silence too. If you know them you can share them if you like to. Simple as that!

[R.G.]

Hi all! thanks you really much for your advice, I have been studying this issue for the last 48 hours I have increased significantly my knowledge on this topic.

Look up "Dunning-Kruger" and think about it.

There is though one thing I don't really understand in this discussion here. Since the question is plain, straight and absolutely technical,

It's because most people don't really understand the technical issues, and the consequences of getting it wrong are so bad.

why do I get all this philosophy talking and opinions which eventually make no sense. In this specific diagram, of this very specific old amp, do you know step by step how to make it a safe amp to use? If not, what's the purpose of all this chatter? I don't really get it

Yes, that last it true. You don't. Worse, you think it's a simple technical question. It's not. And the reason is...

You speak here about a set of tests that an expert would carry out in order to upgrade this amp. OK, which are these tests? Are they some part of a secret bible and they are not allowed to be described? If you don't know them, there is the option of silence too. If you know them you can share them if you like to. Simple as that!

... not as simple as that. The reason is legal liability and moral culpability in dealing with the life of someone who doesn't have the technical background to understand what they're getting into.

If you've read about the Dunning-Kruger Effect, it will also help understand the reticence of the experts. I have had to deal with card-carrying experts who make their entire livelihood on evaluating the electrical safety of equipment, and not one of them would ever tell me "if you do this, your equipment will be safe." They can't - the history of electrical safety has proven too tangled for that, and the remaining "experts" are also smart enough to quit saying how to make things safe.

What they will do is tell you whether your equipment meets certain safety standards. They can tell you whether the standards were met, but they can not and will not tell you whether meeting the standards will be "safe". In fact it is a good test of whether someone really knows about electrical safety: if they say "do this and the equipment is safe", they're not an expert. It's that simple.

I can and shortly will tell you what to do to your amp to make it meet practices that I have seen in the past. I can not and will not tell you that it makes that amp "safe". I can only tell you that this follows practices I've seen before. I unknowingly may be mistaken in some particular, and may leave something out. Can't help that.

1. Remove the "death cap". If it fails, it connects one side of the AC line to chassis ground. For 50% of the ways the line cord can be plugged in, that makes the chassis hot to the AC line, and someone connected to the chassis ground - like, by touching the strings of a connected guitar - will be shocked, perhaps to death, by also grasping something that is connected to earth ground - like a mike stand. Guitarists have actually died this way.
2. Install a three-wire AC cord, including a strain relief that will keep the cord from being cut by the edges of the hole in the chassis, and that's capable of lifting the entire amp by the cord without tearing out. (That last is a rough and ready test the safety guys do a lot.)
3. Connect the AC Line wire to the power switch + fuse side of the wiring leading to the transformer, NOT to the neutral side of the AC line. Do NOT put the switch on one side and the fuse on the other of the incoming AC power. Switches and fuses must be on the line side. It would be much better in this particular amp to put the power switch and fuse into
4. Connect the AC neutral to the other side of the power transformer primary.
In this amp, I would connect AC neutral to the non-tapped side of the power transformer, and put the AC Line side and both switch and fuse in the tapped side.
5. Connect the AC safety ground solidly to the metal chassis. "Solidly" means to drill a hole to be used for a grounding terminal and nothing else, and to sand both sides of the hole. Insert a bolt into the hole from the outside, and put a toothed star washer on the bolt so its teeth bite into the sanded-clean area. Crimp a ring terminal onto the AC safety ground wire, having first made sure that there is more slack in the ground wire than in either the AC line or neutral wires, so the safety ground wire breaks last if a pull is strong enough to pull the cord out. Put another star washer on top of the ring terminal, then run a nut down onto the stack firmly so the star washer teeth bit into chassis, ring terminal and nut and will not come loose in any forseeable event. Do NOT use this nut/bolt connection for any other purpose. Ever.
6. High-pot test the AC power transformer to 4000Vac for one minute. If it arcs, it fails. Actually, that's a minimum. Labs do this to 4200V to provide some margin. But 4000 is the standard, or was when last I read them. The standards change over time. They don't change in the "easier" direction. Failing this test probably destroys the usefulness of the PT.
6. Test the current carrying capability of the AC ground connection to the chassis by using a meter across the connection and applying 25A of power line current through the AC cord to chassis. If it withstands this for ... IIRC, 30 seconds, may have changed ... and the voltage never gets over (can't remember but it's down in the fraction of a volt range) the lab believes that the ground connection can blow a fuse or AC wall breaker, which is what the safety ground connection is supposed to do.
7. Since the B+ is a hazardous voltage, also high-pot test the output transformer. Like the PT, failing this test probably destroys the OT.
8. For extra points (or extra certainty that you won't fry your spouse, your friend, or your child, etc.) make the AC power switch break both sides of the AC line. Oh, yeah, forgot: Make sure the power switch cannot rotate in its mounting hole. I had to do a redesign on some equipment after being failed for that.
9. For extra points, ditch the cable and strain relief, and install an IEC power entry to hold the incoming AC power line.
10. Make sure all the parts on the AC power side of things are marked as passed by UL, CSA, TUV, CE and/or other safety testing organization.

That's the quick and dirty part. It doesn't touch on wire dress and securing, thermal issues, fire safety, or any of about another couple of hundred pages of the standards. I just get tired typing.

Remember - this is just stuff I've seen and had some acquaintance with. I may be wrong, or incomplete. And safety standards change all the time. And standards are not the same as safety.

Questions?

[R.G.]

This kept bothering me during the night. I read back over the posts, and here is some additional information.

The death cap was put in there to reduce hum. The hum it reduces is radio-frequency hum modulated with power line frequency. The way it does this is that it shunts RF on the power line to the "neutral" side of the power line, as this is (kind of) grounded through the wall wiring back at the breaker panel.

Your death cap is rated at 0.02uF 400V, and oil filled. 400V is dangerously low for a voltage rating on a death cap. "X" rated caps are designed to live with and tested for safety standard  conformance for hooking them across ("x") the AC power line. "Y" rated caps are designed and tested to be connected between the AC line and safety ground. These are members of the "suppression film" cap family. You can learn a lot more about line suppression caps here: http://www.justradios.com/safetytips.html

The safest thing to do is to rework the amp to have a three-wire line cord carrying safety ground to the chassis. I have seen lots of people told this that then figure "Well, OK, that's what I should do, but heck, I've used it a long time like this and I haven't died yet, so I'm just going to keep using it like it is. I'll probably be OK. I think." If you fall into this group, I still don't want to later hear that you died, so please, go get an X1 or X2 rated cap. A 0.022uF X2 rated cap costs US$1.70 and is in stock at Mouser Electronics.

And there is another issue here. That's the general skill you can bring to bear on preparing and soldering wires carrying AC mains power voltages. If you don't already know how to do this without endangering yourself and anyone else in the building with the amplifier now and in the future, take the amp to someone how does already know this.

No, the internet is not a sufficient place to read about and learn this, just like you can't learn surgery by reading the internet.