writes:

Did some experiments on the fuse of my amp... I replaced a 500mA 250v
fuse with a 1.6a 125v fuse and found the sound much improved. Then I
decided to replace the 1.6a fuse with a jumper made of a silver
paperclip, and found the sound improved much further. Then I replaced
the paper clip with silver solder, and found it improved further
(though I'm less sure about the solder being better than the clip
overall...).

I doubt that you could hear the difference of changing the fuse,
especially if you are changing the main amplifier use.

I think what you heard is caused memery by the psychological effect
that you though you were improving the device by changing the
fuse.

The original fuse is pretty low resistance already, a 500 mA
fuse having typically resistance of less than 0.5 ohms and maximum
voltage drop of 230 mV.. Those are pretty little when comparing
to mains voltage coming in and also to the other resistances on
the system (mains wiring in wall, inside equipment, mains
transformer primary resistance etc..).

I quess that in real life systems if changing that fuse had
any noticeable effect on the audio amplifier, that amplifier
was not well designed, and turnign other loads on your house
on/off would have more effect on the amplifier performance
than changing the fuse.

Source for fuse information:
http://www.cooperet.com/library/products/GMA_Specs.pdf

Question is: Exactly what risks are there in running an integrated amp
or a preamp sans fuse? I don't care so much about the gear blowing up,
since its old gear anyway. But nor do I want a fire started when I
leave the amp running all night or am not at home.

Running the equipment without fuse has a very considerable fire risk!
If somethign fails inside your equipment (can fail more often when
equipment gets old), then in case of short circuit on the electronics
the equipment mains fuse normally blows before smoke starts coming
out..

If you take out the fuse, then in case of short circuit your
equipment starts easily taking lots of mains power...
When transformer output is short circuited it can easily take
10 times more than it's rated power from mains.
This power gets dissipated inside your equipment at some place
(usually most in transformer, some power on wiring and component
where short circuit happened)... Things will prety quicly get
quite hot... bad smell amd smoke coming out..
If you are lucky the transformer primary might burn cut
or your main fuse on your distribution panel blows... in less
fortunate case the flames start coming out together with the
smoke from your equipment.

It is dangerous to run equipment without fuse or wrong size fuse.
It can easily burn down your house. And if your insurance company
finds out that you intentianally replaces your fuses with
something else, they most definately will not pay any money to you.
So if this gambling you made on operating equipment without proper
fuses blows, you will need to start thinking what is to live
without your house and things inside it and no compensation for
them. And possibley killing/injuring/harming somebody else living on the
house or nearby, and getting sued because of the illegal electrical
modifications you made to your equipment that caused that fire!

Th equipment are originally designed to be operated with the
proper fuses installed in them. When used in this way they should
be reasonably safe (very unlikely to burn down your house).
If you take the fuse protection, then one very necessary layer
of security is taken away.

In the case of the
preamp, the casing is solid metal, with the integrated, its a wood
casing. What are the chances of fire and how would it start?

If you operate them withotu fuse and a serious short circuit
happens inside those equipment, then I think yo have soemthing
like 20-50% change of getting fire on that case!
That's just quessing. The percentages can vary greatly
depending on their construction and their mains amplifiers.

What are the chances of it blowing up and how might that occur?
(so far, no problems!).

Hard to say. But there are real changes.
As you know from other electrical equipment, they will not
last forever.. usually fail within 5-20 years more or less...

Is electrical shock a risk with a fuseless amp?

Not considerable grater than with properly fused amplifier I think.

The fire risk is your main risk you need to worry about.

--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/