Help! tube amp burnt?

[flatsound]

Hi guys


I have an "old" Icon audio 40, it has been working fine but yesterday I heard a big pop coming from the right speaker. Today the same hapened again but that noise was stronger, then i switched off the amp but I could smell something burninng in side. I opened the amp and I could see what I think that is a resistor burnt.

I can simply replace that resistor but I have no idea what was the cause. I'd like to know to avoid other problems.


Here are some pics with a darker resistor (in the midle of the picture)

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

Thanks in advance.



Regards

flatsound

 

[Wavebourn]

Looks like the tube has a burnt loose wire on a screen grid that shorted on a suppressor that is connected to cathode. Put a new tube and replace the resistor (it's so called screen grid stopper). Don't forget to rebias the output stage.

 

[Ty_Bower]

It looks like it's a resistor in series with the screen grid (pin 4) and using the non-connected pin 6 as a tie point. There may be an ultra-linear screen tap from the output transformer (orange lead?) landed on pin 6? It's difficult to tell - the photo is somewhat fuzzy. Use the macro setting (little flower icon) on your camera if it has one, and do not use any telephoto (don't zoom in).

 

[flatsound]

Thanks for your opinions guys

By the way, can you recommend an easy book about that subject? A nice and easy book always can be usefull in the future for a neewbe like me.


Thanks a lot




regards

flatsound

 

[flatsound]

Finally some good pics. Ty_Bower, thanks for your sugestion about the pics


http://img200.imageshack.us/gal.php?g=mytubeamp2019.jpg




Regards

flatsound

 

[llwhtt]

Generally the only reason for a screen resistor to go up in smoke is a bad tube. As suggested earlier replace the resistor(100 Ohms?) and the tube. Then check bias and adjust if necessary.

Craig

 

[bacon665]

Might be worth it to change to a ceramic insulated wirewound resistor, they can take more abuse then the polyester (im assuming thats what burnt) and have less signal drift in MOSt applications.
There are always exceptions to this though.

 

[flatsound]

Thanks for your replies guys.

llwhtt, Yes the value resistor is 100 ohms, +/-5%. The color strips are Brown, Black, Brown and gold.

Do you sugest any website to buy it from? Preferably English ones.

 

[bigwill]

Thanks for your replies guys.

llwhtt, Yes the value resistor is 100 ohms, +/-5%. The color strips are Brown, Black, Brown and gold.

Do you sugest any website to buy it from? Preferably English ones.

Farnell, CPC (part of farnell), Radio Spares, eBay

 

[bacon665]

tube depot has nice resistors if you need carbon.metal oxide and high power.
http://www.tubedepot.com/resistors.html
i cant tell if the ones in your picture are half watt or quarter

it looks to be the metal oxide resistors here http://www.tubedepot.com/r-283.html