Tweed Champ Not working.

So I completed my first build, a 5f1 tweed champ. Everything worked fine for about a week.

I went to go use it one day and it would not work, it had power, the fuse was fine, the tubes all lit up, nothing obviously wrong...

The 10k 2w B+ resistor on the bottom left of the board was burnt out.

http://4.bp.blogspot.com/_BYIkYo9cnnw/TFKX7Mx3RhI/AAAAAAAAACU/ZRmuoL_ZBC4/s1600/champ_5f1_layout.gif

It looked like it was slowly baked as opposed to just burning out abruptly.
I ordered the replacement for it, but what would cause this? How could I prevent this from happening again?

Thanks!
 

wakibaki

Banned
2008-01-08 11:51 pm
It looked like it was slowly baked as opposed to just burning out abruptly.
I ordered the replacement for it, but what would cause this? How could I prevent this from happening again?

It could just be that the air circulation around the resistor was poor, if it was mounted on turret board it should be spaced off the board. This is probably not a sufficient explanation on its own, but it's difficult to be definitive.

When you first assembled the amp, did you measure the components as they went in? You should also note the voltages are roughly as stated on the diagram, and write the readings on a diagram of your own. This gives you a cross check that you have assembled the amp correctly and that the components are within tolerance, and that there are no coincidental adverse tolerances. When you have the resistances and the voltage drop across them you can calculate the the currents through them and their power dissipation. A valve amp can work when quite a long way out of spec, so the fact that it was working immediately after you built it is no guarantee that it was built correctly.

w