The key to this kind of soldering is to be careful and slow as you'll be working with a powerful flame. Other types of flameless soldering irons, guns etc would most probably be too weak as the areas & parts to solder are big and the instrument itself also acts like a radiator, taking heat away from the point being soldered. So something strong is needed.
A hand type torch did the job for me. The soldering took a bit long as even this torch is a bit weak for this kind of job.. But I guess it is better this way, as it makes making mistakes a bit more difficult also.
I've bought soldering wire a bit thicker than electronics soldering wires. This one I bought has 2.5-3mm diameter.
I've also tested the electronics soldering wire, it is too thin. It melts and drips to the ground, just at the moment it gets a little close to the flame, without even touching the point to be soldered.
Trumpet v Cornet. The Trumpet and Cornet are both very similar members of the Brass instrument family. However, they are generally used for different styles of music. Many advanced players are competent on both. So, what exactly are the differences between the two?
The sequence of soldering for me is as follows;
1-Clean the area of solder, by sand paper if possible. If too tight for sand paper, a thin metal tip or small blade can also work.
2-Heat and apply soldering resin.
3-Continue heating for 15 seconds or so.
4-Point away the torch and simultaneously touch to both of the surfaces to be soldered with the tip of the soldering wire and push it into the gap, trying to melt it with the heat of the metals as it goes in. If it doesn't melt this way, either try a thinner soldering wire or get the flame a bit closer while pushing the solder wire in.
5-Do not put on too much solder at once, melt small drips and let them flow into the broken joint, filling the gaps.
6-Slowly rotate the instrument while heating to let the liquid solder to flow towards where you want it to.
7-When the bond seems ok, cool & harden it with a spray of water to prevent solder to flow out of the joint.
8-Do not hesitate to heat the instrument as it is not possible to do soldering without the surfaces reaching the necessary temperature. But do not exaggerate, some other soldered parts of the instrument may become loose or the lacquer layer may burn. Be careful and heat only where heat is necessary.