Torroidal madness?

[Phil Allison]

Hi all,

recently I replaced a toroidal mains transformer in a 5 or 6 year old Crown XLS602 power amplifier. This was a 240V, 800VA size tranny with the secondary winding giving of 75-18-0-18-75 volts.

http://cdn.avsforum.com/3/38/38365662_vbattach143596.jpeg

The toroidal was made by a Chinese company - NRE Electrical Manufacturing Co Ltd.

www.fsnre.com

The primary had shorted turns and luckily I had another very similar toroidal on hand that did the job - after adding a small 18-0-18 tranny as well. No other faults were found with the amp.

Failures of such large transformers is quite rare, so I began to unwind the thing to have a look and also get some heavy gauge winding wire too. It was a real bugger of a job cos both the secondary and primary had been "bi-filar" wound. The shorted turns were found near the core, right where the twin primary winding is split and series wired. No big surprise there.

But then there WAS a big surprise underneath - the toroidal core itself. Normally there are precision made, tape wound cores with molded plastic caps covering the sharp edges. Not this one.

The corner edges had simply been ground off by hand and covered in cloth tape. The core itself looked rough and uneven - then I realised it was made from dozens of separate strips of steel, spot welded to each other, end to end and of varying thicknesses and widths. The tranny was made from scraps !!

Some dirt poor Chinese had hand assembled the core using rusty off cuts and sweepings from the floor from some transformer factory. The centre hole was perfectly round but the outside diameter varied by 3mm due to all the joins.

One would reasonably suspect such a "Frankenstein" core of having poor magnetic performance - but all my testing showed it was perfectly OK.

The Chinese are getting desperate.



... Phil

[William Sommerwerck]

"Phil Allison" wrote in message
news:74b01fcb-f8a3-4ed4...@googlegroups.com...

> The Chinese are getting desperate.

Which is basically good for the West.

After WWII, the Japanese realized they had to export high-quality products to
compete. Not all Chinese manufacturers have caught this, and some compete
solely on the basis of price. Until they do, they will never be the real
threat they have the potential to be.

I'm reminded of the joke about Japanese products in "BttF 3".

[Mike]

But perhaps there are also rich Chinese who will pay good money for a
genuine hand-made artisanal artefact!

Mike.

[Cydrome Leader]

Phil Allison <palli...@gmail.com> wrote:
>
> Hi all,
>
> recently I replaced a toroidal mains transformer in a 5 or 6 year old Crown XLS602 power amplifier. This was a 240V, 800VA size tranny with the secondary winding giving of 75-18-0-18-75 volts.
>
> http://cdn.avsforum.com/3/38/38365662_vbattach143596.jpeg

That thing looks awful. nasty silicone-looking glue and sloppy cable ties parts buried under other parts. It is amazing fans cost less than real heatsinks these
days.

> The toroidal was made by a Chinese company - NRE Electrical Manufacturing Co Ltd.
>
> www.fsnre.com
>
> The primary had shorted turns and luckily I had another very similar toroidal on hand that did the job - after adding a small 18-0-18 tranny as well. No other faults were found with the amp.
>
> Failures of such large transformers is quite rare, so I began to unwind the thing to have a look and also get some heavy gauge winding wire too. It was a real bugger of a job cos both the secondary and primary had been "bi-filar" wound. The shorted turns were found near the core, right where the twin primary winding is split and series wired. No big surprise there.
>
> But then there WAS a big surprise underneath - the toroidal core itself. Normally there are precision made, tape wound cores with molded plastic caps covering the sharp edges. Not this one.
>
> The corner edges had simply been ground off by hand and covered in cloth tape. The core itself looked rough and uneven - then I realised it was made from dozens of separate strips of steel, spot welded to each other, end to end and of varying thicknesses and widths. The tranny was made from scraps !!
>
> Some dirt poor Chinese had hand assembled the core using rusty off cuts and sweepings from the floor from some transformer factory. The centre hole was perfectly round but the outside diameter varied by 3mm due to all the joins.

fascinating.

> One would reasonably suspect such a "Frankenstein" core of having poor magnetic performance - but all my testing showed it was perfectly OK.
>
> The Chinese are getting desperate.

such a crappy transformer is slightly brilliant though. Somebody took the time to try that hack.

[Phil Allison]

Cydrome Leader wrote:

> Phil Allison

> >
> > http://cdn.avsforum.com/3/38/38365662_vbattach143596.jpeg
>
> That thing looks awful.

** Its actually rather well made - Crown Audio are not mugs.

nasty silicone-looking glue

** Huh ?

and sloppy cable ties parts buried under other parts

** Not true.

> It is amazing fans cost less than real heatsinks these days.

** It has always been so.

> > The Chinese are getting desperate.
>
> such a crappy transformer is slightly brilliant though. Somebody took the time to try that hack.

** Yeah - I came to the same conclusion.

The Chinese guy who discovered you *could* wind perfectly usable and sellable cores using scraps welded end to end must have got a few big pats on the back - or an extra bowl of rice & fish.

BTW:

The same amp has a novel feature not seen by me before. In faulty condition, it drew about 10mA of AC current while having no DC rails and there was a faint smell of something hot.

Turns out, it has a soft start circuit consisting of a relay and a PTC in parallel. No, not an NTC - a *PTC* !!

A coin sized device made by "Epcos" that has 6 ohms cold resistance and jumps to circa 20kohms if overheated - and it can tolerate 240VAC.

So, if the DC supply does not come up in the first 100mS, the PTC goes high and that is that. Brilliant.


.... Phil

[Mook Johnson]

I believe some loudspeakers use that trick in tweeter and midrange
crossovers. They called them "polyswitch" to protect them from too much
continuous power.

Never used them but saw them referenced in Infinity, Polk and other
consumer high'ish' end ($800+/set)loudspeakers of the 90's.

[Phil Allison]

Mook Johnson wrote:

Phil Allison wrote:
> >
> > The same amp has a novel feature not seen by me before. In faulty condition, it drew about 10mA of AC current while having no DC rails and there was a faint smell of something hot.
> >
> > Turns out, it has a soft start circuit consisting of a relay and a PTC in parallel. No, not an NTC - a *PTC* !!
> >
> > A coin sized device made by "Epcos" that has 6 ohms cold resistance and jumps to circa 20kohms if overheated - and it can tolerate 240VAC.
> >
> > So, if the DC supply does not come up in the first 100mS, the PTC goes high and that is that. Brilliant.
> >

>

> I believe some loudspeakers use that trick in tweeter and midrange
> crossovers. They called them "polyswitch" to protect them from too much
> continuous power.

** Been using Polyswitches for decades.

They are not suitable for 240VAC use and have far too low cold resistance values like 0.1 ohms.

The Epcos PTC has 6ohms cold resistance and can be connected directly across the AC supply with NO harm despite dissipating 10kW for a few milliseconds.


.... Phil

[Cydrome Leader]

Phil Allison <palli...@gmail.com> wrote:
> Cydrome Leader wrote:
>
>> Phil Allison
>> >
>> > http://cdn.avsforum.com/3/38/38365662_vbattach143596.jpeg
>>
>> That thing looks awful.
>
> ** Its actually rather well made - Crown Audio are not mugs.
>
> nasty silicone-looking glue
>
> ** Huh ?

I see a red wire glopped to the board at the ends and sort of cable tied
to another brown wire. It makes no sense. Replacing one filter cap will
surely tear the PVC sleeve off all the caps touching it. I really hate
that glue stuff.

> and sloppy cable ties parts buried under other parts
>
> ** Not true.

How do you replace the lower right TO-3 transistor in the photo? From what
I can tell, you need to remove two more transistors and the headsink that
blocks the one buried under it. It's got that build once, service never
look and feel.

The output and power wiring look nice though.

>> It is amazing fans cost less than real heatsinks these days.
>
> ** It has always been so.

If a fan dies in that thing does it go into some sort of protection mode
or does it just blow up?

>> > The Chinese are getting desperate.
>>
>> such a crappy transformer is slightly brilliant though. Somebody took the time to try that hack.
>
> ** Yeah - I came to the same conclusion.
>
> The Chinese guy who discovered you *could* wind perfectly usable and sellable cores using scraps welded end to end must have got a few big pats on the back - or an extra bowl of rice & fish.
>
> BTW:
>
> The same amp has a novel feature not seen by me before. In faulty condition, it drew about 10mA of AC current while having no DC rails and there was a faint smell of something hot.
>
> Turns out, it has a soft start circuit consisting of a relay and a PTC in parallel. No, not an NTC - a *PTC* !!
>
> A coin sized device made by "Epcos" that has 6 ohms cold resistance and jumps to circa 20kohms if overheated - and it can tolerate 240VAC.
>
> So, if the DC supply does not come up in the first 100mS, the PTC goes high and that is that. Brilliant.

Interesting. Sounds like a built in version of running TV in series with a
light bulb to check for other faults after replacing the horizontal output
transistor.

[Cydrome Leader]

it seems like a race to the bottom for most products though. Those of who
who want quality over price are a very, very small minority when it comes
to total numbers.

Hell, even Klein Tools is pushing chinese junk now.