John Curl's Blowtorch preamplifier part II

[Kindhornman]

ES,
Don't they call those testers a Megger's for that types of high voltage testing. I do remember my electrician would use one to find a bad motor insulation or bad wires arcing somewhere. If I remember correctly it was a high voltage for a very short duration. I wouldn't think they would be that expensive even for a new meter.

 

[simon7000]

ES,
Don't they call those testers a Megger's for that types of high voltage testing. I do remember my electrician would use one to find a bad motor insulation or bad wires arcing somewhere. If I remember correctly it was a high voltage for a very short duration. I wouldn't think they would be that expensive even for a new meter.

The Megger is the variety used for linemen. The price would fool you! The oldest ones had a crank so that you made the high voltage. Once transistors caught on they became battery operated. Much easier to use. The crank models became collectors' items.

Just checked, boy have prices come down! Also new hand cranked ones from China!!

 

[gpapag]

About Megger®
For over 100 years, Megger has been the premier provider of electric test equipment and measuring instruments for electrical power applications. The company was founded in 1889 in England as Evershed & Vignoles and over the years has been known by several names, most recently, AVO International. In 2002, the company decided to change its name to Megger, which is what many people have called it all along. Today, Megger enjoys an outstanding reputation in the areas of insulation testing, low resistance and ground resistance testing, and a wide variety of electrical contractor maintenance tools such as multimeters, portable appliance testers and clamp-on meters.

For many years, the James G. Biddle Company in Pennsylvania, was the U.S. importer of Megger products and they also manufactured equipment under their own name. A number of years ago, Megger became the sole owner of James G. Biddle, and has retained the use of the Biddle trademark for many of the Biddle products still available today. Manufacturing insulation testers is where Megger started, and the Megger brand name is so well known today that maintenance professionals often incorrectly use it as a verb when they refer to doing an insulation test on wiring. The Megger trademark was first registered in May 1903 by Evershed and Vignoles and it, along with "Biddle" are jealously guarded by the company today.

George

 

[Kindhornman]

George,
Tanks for the history lesson. I will say that I heard the word Megger used as a verb, kind of like Kleenex a brand name that becomes the standard reference for the entire field. Never paid any attention to the brand, just what it was used for.

 

[Elvee]

And no, I do not have the capability od passing 2.5 kV anywhere, nor are the cpacitors meant to go that high.

The X rated capacitors you use are able to withstand much higher voltages than their nominal 250 or 275V: if they are of the most common X2 class, their test voltage is 2.5kV.
X1 or X3 also exist, but are much rarer: I have never seen a single X3 in all my career (1.2kV). X1 types withstand up to 4kV.
In addition, they may not suffer catastrophic failure leading to a short or a fire for example: their failure mode is degradation, leading to a loss of some capacitance.
There is no risk testing them at this level, on the contrary it is advisable

 

[dvv]

The X rated capacitors you use are able to withstand much higher voltages than their nominal 250 or 275V: if they are of the most common X2 class, their test voltage is 2.5kV.
X1 or X3 also exist, but are much rarer: I have never seen a single X3 in all my career (1.2kV). X1 types withstand up to 4kV.
In addition, they may not suffer catastrophic failure leading to a short or a fire for example: their failure mode is degradation, leading to a loss of some capacitance.
There is no risk testing them at this level, on the contrary it is advisable

I am an outlaw, I do NOT use X-rated caps bevause they are junk in my view. Instead, I use Wima MKS rated at 630VDC.

 

[fas42]

Removing noise in favor of signal is such a claim.

The principle is very straighforward: what you hear is a mix of the audio signal, derived from the source mechanism, and additional 'noise' due to the playback mechanism not working "perfectly". When that ratio is too degraded, the noise is too intrusive, then you have unpleasant listening - so the simple objective is to reduce the noise component, by all means possible - "weird things" is one way to go, if that tickles your fancy.

The signal never "gets better", it just has less muck mixed in with it - nothing more ambitious than that ...

 

[fas42]

So far I have had problems with only one unit, so I kep thet one because I want to find out exactly why it behaves funny upon switch on, which means upon plugging the cable into the socket or the other side into its input IEC recepatcle. Sometimes spark appear and it's tripped the line 16A (at 220 VAC) fuse a few times. No obvious reason, but to me this is serious midbehaving. I reckon it ain't smarter than me, so I want to know what gives. Never before, never after that one sample. It's a great who done it police story.

Just a gut feeling, Dejan, but it's possible that on that unit the parts are so well balanced, purely as a random occurrence, that the current surge is a sharper, and higher peak - hence fuse blows. On other units the natural variability between nominally identical parts is enough to blur that sharpness, the Q of the unit, so to speak, and they don't "play up" - try changing one or two parts with spares, and see if the problem goes away.

 

[fas42]

Only now, 7 hours later and playing the same disc do I realise what it is... its part of the music. There was just no way that sound came from the speakers, it was to real and "external". Of course now that I know , its a slightly different story, its not quite as real because I now know. First time round though and I truly didn't make the connection.

A quite amazing experience.

Hey, don't knock it! - you just had a dose of convincing sound, it's quite addictive when it happens continuously ...

Being "too real and external" is the name of the game ... personally, I have zero interest in having speakers yelling at me all the time, "Hey, look at me, look at mooii ... "

 

[gpapag]

George,
Thanks for the history lesson. I will say that I heard the word Megger used as a verb, kind of like Kleenex a brand name that becomes the standard reference for the entire field. Never paid any attention to the brand, just what it was used for.

Working in aviation maintenance hangars for long eh?

I am an outlaw, I do NOT use X-rated caps bevause they are junk in my view. Instead, I use Wima MKS rated at 630VDC.

Dejan, X (and Y)-rated caps self healing behavior is specified (i.e. safety agencies tested)

George

 

[freax]

If so this could be tested by capturing the event on an oscilloscope and watching for oscillation. Capacitors which measure out of tolerance or significantly different from their original measurement would also be an indication.

That would be a pretty violent event on the oscilloscope. I'd pay to see that.

As for IEC connections, they are notorious in the computing field for arcing or making a bad contact, especially when you mix and match different makers together like has been done.

https://www.youtube.com/watch?v=MQCk-1tP2sQ

Other than that it could be a socket on the outputs that has a short or fault somewhere which clears up once turned on. Strange but has been done.

Infact I only need to travel 5 meters to my kettle to see arcing and heating of the socket to see a badly made IEC socket/plug. A good press of the plug into the socket is usually enough to fix it.

I would wire a mains lead directly into the filter with a grommet like in ye olden days.

 

[wrinkle]

I am an outlaw, I do NOT use X-rated caps bevause they are junk in my view. Instead, I use Wima MKS rated at 630VDC.

One reason paper is favoured as the dielectric for X rated caps is that the oxygen content on the molecule means there is less carbon in the residue after an arc, so any damage is less likely to lead to an increase in leakage current or catastrophic failure.

 

[dvv]

Just a gut feeling, Dejan, but it's possible that on that unit the parts are so well balanced, purely as a random occurrence, that the current surge is a sharper, and higher peak - hence fuse blows. On other units the natural variability between nominally identical parts is enough to blur that sharpness, the Q of the unit, so to speak, and they don't "play up" - try changing one or two parts with spares, and see if the problem goes away.

Anything is possible, FRank, but as soon as I move back into my old room, I will get to the bottom of it.

 

[dvv]

Dejan, X (and Y)-rated caps self healing behavior is specified (i.e. safety agencies tested)

George

I am aware of that George, but I also know how my system sounds with them and how with the Wimas. I am not willing to kill an otherwise good product by changing to comply with the law. Fortunately, I don't have to, the law is clear ion that, only mass manufactured items going through the retail chain must, individuall sold and purchased items do not have to. Whereas the regualtions on electrical safety must be obeyed by all.

 

[dvv]

That would be a pretty violent event on the oscilloscope. I'd pay to see that.

As for IEC connections, they are notorious in the computing field for arcing or making a bad contact, especially when you mix and match different makers together like has been done.

https://www.youtube.com/watch?v=MQCk-1tP2sQ

Other than that it could be a socket on the outputs that has a short or fault somewhere which clears up once turned on. Strange but has been done.

Infact I only need to travel 5 meters to my kettle to see arcing and heating of the socket to see a badly made IEC socket/plug. A good press of the plug into the socket is usually enough to fix it.

I would wire a mains lead directly into the filter with a grommet like in ye olden days.

So would I, and in fact originally did just that, but then people yelped that they had spent loads od dough on super duper power cables and now they can't use them.

Admittedly, the IEC solution is much more practical for me, due to unbeliveble differences in wall socket plugs existing around the globe. Nevertheless, I always prefer the solution with less contact points, or, if there must be a contact, then let it be a soldered one. All contact points are crap, soldered is only the smallest crap around.

 

[keantoken]

I tried some of the new Panasonic ECWFD with integral fuse across the line. After a week or so they started buzzing, although they still measure an okay capacitance. I suspect they were damaged by a spike which created a spark gap inside the cap which snaps at each peak. It would be interesting to know exactly what the mechanisms at work here are.

 

[freax]

http://shadytreeprojects.com/index.php?title=Why_I'm_not_using_IEC_(Jug_Cord/Plug)_Sockets_anymore.

 

[Elvee]

I am an outlaw, I do NOT use X-rated caps bevause they are junk in my view. Instead, I use Wima MKS rated at 630VDC.

You are an outlaw, and a not very sensible person: if your filter causes a fire, you will be responsible.
General purpose mylar caps like the MKS are not well suited for this kind of job, and your present spark problem could very well find its origin in one of the caps.

You have no excuse for not using proper capacitors: there are X-rated PP series performing better than your MKS: look at Epcos for example

 

[dvv]

These are your opinions which I obviously do not share.

 

[freax]

They're not safe in mains conditions. Regardless of how better they make things sound.

Mains electricity is full of transients and spikes way higher than 630vDC. Causes and Effects of Transient Voltages

The vast majority of transients are produced within your own facility. The main culprits are device switching, static discharge, and arcing.

Each time you turn on, turn off, load, or unload an inductive device, you produce a transient. Inductive devices are those devices that use "magnetic mass" to function. Examples of inductive loads are motors and transformers. The inductive "kick" from a 5-horsepower motor turning on can produce a transient in excess of 1,000 volts.

Its pretty obvious that one of the caps are damaged and is shorted internally.