Help! tube amp burnt?

flatsound · 18th June 2009, 10:16 PM

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)

[IMG]
http://http://img190.imageshack.us/i...mpunder003.jpg[/IMG]

Thanks in advance.

Regards

flatsound

Wavebourn · 18th June 2009, 10:31 PM

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 · 18th June 2009, 10:36 PM

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 · 19th June 2009, 03:05 PM

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 · 24th June 2009, 10:50 PM

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 · 24th June 2009, 11:22 PM

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 · 24th June 2009, 11:43 PM

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 · 25th June 2009, 05:47 PM

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 · 25th June 2009, 06:12 PM

Quote:

Originally posted by 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.

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

bacon665 · 26th June 2009, 02:41 AM

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

18th June 2009, 10:16 PM	#1
flatsound diyAudio Member Join Date: Jun 2009	Help! tube amp burnt? 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) [IMG] http://http://img190.imageshack.us/i...mpunder003.jpg[/IMG] Thanks in advance. Regards flatsound

18th June 2009, 10:31 PM	#2
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	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. __________________ The devil is not so terrible as his mathematical model! Wavebourn: We Create Creativity!

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18th June 2009, 10:36 PM	#3
Ty_Bower diyAudio Member Join Date: Mar 2007 Location: Newark, DE	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).

19th June 2009, 03:05 PM	#4
flatsound diyAudio Member Join Date: Jun 2009	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

24th June 2009, 10:50 PM	#5
flatsound diyAudio Member Join Date: Jun 2009	Finally some good pics. Ty_Bower, thanks for your sugestion about the pics http://img200.imageshack.us/gal.php?g=mytubeamp2019.jpg Regards flatsound

24th June 2009, 11:22 PM	#6
llwhtt diyAudio Member Join Date: Jun 2008	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

24th June 2009, 11:43 PM	#7
bacon665 diyAudio Member Join Date: Apr 2009	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.

25th June 2009, 05:47 PM	#8
flatsound diyAudio Member Join Date: Jun 2009	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.

26th June 2009, 02:41 AM	#10
bacon665 diyAudio Member Join Date: Apr 2009	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

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