Hot Q2 transistor ~ Surf PI kit?

[Bart]

Just curious about something... I built a small flat spiral coil to test with last night... 17 turns, 20 gage coil wire. However the coil is only 4" inches across. This coil was working much better than the first one I made which was a simple 4" loop using 22 Gage with 27 turns. It seemed to be working great, much more sensitive untill I noticed that Q2 transistor was getting really hot... Too hot to touch, so I unhooked the battery. If I'm not paying to close of attention to using a coil with the right amount of turns and correct gage for the circuit... and I didn't use the coil calculator for either coil.... Is this the out come? Q2 gets burning hot? The first coil I made didn't seem to make the transistor get hot at all?

I need to do more experiments here...

[Qiaozhi]

Just curious about something... I built a small flat spiral coil to test with last night... 17 turns, 20 gage coil wire. However the coil is only 4" inches across. This coil was working much better than the first one I made which was a simple 4" loop using 22 Gage with 27 turns. It seemed to be working great, much more sensitive untill I noticed that Q2 transistor was getting really hot... Too hot to touch, so I unhooked the battery. If I'm not paying to close of attention to using a coil with the right amount of turns and correct gage for the circuit... and I didn't use the coil calculator for either coil.... Is this the out come? Q2 gets burning hot? The first coil I made didn't seem to make the transistor get hot at all?

I need to do more experiments here...

A 17 turn 4" diameter coil (jumble wound) will only have an inductance of 69uH. As your coil is spiral wound, it will be even less. No wonder Q2 is getting hot. For a 4" jumble wound coil, you'll need about 40 turns. This will give an inductance of 346uH. Add more turns if you plan to wind it in a spiral.

[Bart]

Thanks Qiaozhi... Math is not my best subject, however is there a formula I can use, or is there a way to test the coil by itself using a multimeter so I won't have this happen again and I will have my inductance within the correct range?? Or maybe I should just stick to using the coil calculator. I've put together quite a few electronics from using schematics, including this surf PI kit... Worked correctly first time I hooked up the battery, (except I had to switch R22 and r18 due to the mistake I read about).... but my understanding of the math behind what's actually happening within the components isn't that great... so my electronics theory knowlege is fairly basic.

[Qiaozhi]

Thanks Qiaozhi... Math is not my best subject, however is there a formula I can use, or is there a way to test the coil by itself using a multimeter so I won't have this happen again and I will have my inductance within the correct range?? Or maybe I should just stick to using the coil calculator. I've put together quite a few electronics from using schematics, including this surf PI kit... Worked correctly first time I hooked up the battery, (except I had to switch R22 and r18 due to the mistake I read about).... but my understanding of the math behind what's actually happening within the components isn't that great... so my electronics theory knowlege is fairly basic.

The coil calculator is here ->
http://www.geotech1.com/forums/showthread.php?t=17909
Although you're probably already aware of this.
You will need to purchase an inductance meter to test your coils, or you could build your own from one of the available kits.

[Bart]

OK thanks again Qiaozhi! Just checked on ebay.. Looks like I could get an inductance meter fairly cheap.