On Sat, 12 Mar 2016 10:32:24 -0000, "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.

It's a cost and marketing consideration.

This product doesn't carry UL safety listing, so the issue of fuse
behaviour under single-fault abnormals may never have been raised. As
it is in low voltage circuitry, the issue may never have been raised.

The use of wire fuses, even when considered acceptible, required
dedicate hardware and specific wire manufactured for that purpose in
potentially hazardous applications. This application represents an
energy hazard, rather than a shock hazard. Low voltage fuses with DC
ratings are expensive, but do exist.

RL