On 3/12/2016 2:32 AM, Gareth Magennis wrote:
Here's something I've not seen before.

A Power Amplifier has binding posts which you are supposed to solder
wire between, instead of fuses.
This is on the low voltage power supply. The wire fuses go to the
bridge rectifier/10,000uF caps, and supply the +/- 15v supplies.

The PCB is inscribed "wire Cu 0.25mm" and also designated F2 and F3.

And yes, there is (or was) thin copper wire soldered in place on both
identical channels of this amp.
(One side has melted both these wire fuses, as the caps are bad)



Why would a manufacturer do this? I'd be inclined to put back wire
ended fuses.


I'm guessing 0.25mm means 0.25mm Cross Sectional Area rather than
diameter, but it is not clear.
The following table gives 6A and 15A for each possibility, which seems
quite high for a low voltage supply.
http://www.gxk.org.uk/info/wire.htm

I took out a small remaining piece of the wire and it actually measured
just below 0.5mm diameter, but this is not a reliable measurement as the
wire has obviously suffered trauma.






This is the amplifier in question:
http://www.kv2audio.com/products/esr...s/esr2800.html



Cheers,


Gareth.
The reason is the circuit has a BIG inrush current. A regular fuse
material takes a bit of time to open, but if the current is below, but
close to the rated current, the fuse material will soften and sag, and
get thinner after many uses. A copper wire will not do this, but will
melt at the rated current you found.

My plant uses three 200 amp services with meters. They are fused for 200
amps with silver fuses. They do blow at a small percent above 200 amps
and almost instantly, and cost $75 each to replace.

Paul