From time to time, a short subject comes up that needs a few words of explanation, or just a place to write it down so I don't forget. This is that place!
Fuses prevent the damage that can happen when too much current flows for too long. There's a general hierarchy of how long the fuse will tolerate a current near or above its rated value:
You'd thing that's all there is, but it turns out that there are even significant variations within a category, especially the slow-blow category. Fuses are measured for their I^2*t tolerance. Why? Fuses have a certain nominal resistance, so the power dissipated in the fuse is I^2*Rfuse. The amount that the temperature rises is proportional to the time that the power is present, so we have hand-waved our way to I^2*t. If the fuse gets hot enough, the fuse wire melts and the circuit is opened.
Let's take an example. We use a 1.6 Amp Slow Blow fuse in the 240 Volt version of the GT-102. There was a report of occasional nuisance fuse blowing in otherwise good 240 Volt GT-102's. When I looked into it, it turns out that the original fuses had just 1/4 the I^2*T, the rating of the fuses that I currently ship. This is so even though they both have the same 1.6 Amp rating.
This section points out some problems that can get in the way of accurate measurements for both low and high value resistors
Before measuring a low-value resistor, it's important to "zero the meter". Connect the ohm-meter probes together and look at the ohm-meter display. Ideally, it would be 0.0 Ohms, but it will typically be a few tenths of an ohm, maybe up to about 1 Ohm. This is quite important! Imagine that you're trying to measure a 0.5 Ohm resistor, but you didn't realize that your meter reads 0.8 Ohms with both leads touching. Even if the 0.5 Ohm resistor were exactly correct, you'd see 1.3 Ohms on the display, and you'd erroneously conclude that the resistor is out of spec!
If you're measuring a high value of resistance, for example 3.3 Meg-Ohms, you must be careful to not let the probes touch your fingers. Why? Because if the probes touch your left hand and your right hand as well as the resistor, then your body resistance will appear in parallel with the 3.3 Meg-Ohm resistor you're trying to measure. Take the example when you're measuring a 3.3 Meg Ohm resistor, and your body resistance is in parallel with the resistor. If your body had a resistance of 3 Meg Ohms, then the 3.3 MegOhm resistor would read as 1.57 Megs. The proper way to measure a high value resistor is to make sure that your probes only touch the resistor leads, and nothing else that is conductive that would provide a leakage path across the resistor to corrupt the measurement.
How do you know if a transistor is good? By good, I mean not open or shorted. That it's likely to behave like you'd expect when you put it into a circuit. This video shows how to use a DMM (Digital Multi-Meter) Diode check to see if a transistor is working.
This whitepaper shows how to disable AGC in the PC version of Zoom. Disabling AGC (automatic gain control) lets Zoom reproduce dynamics, rather than washing them out.