Blown up resistor in S-5 amp kit...

fenpark15 · 29th December 2007, 04:55 PM

I just finished my s-5 k-16LS kit and plugged it in for my first ever tube experience. There was a loud pop and a bright light and that's it. I'm hoping someone can help me figure out what went wrong.

The resistor that blew up was a bleeder resistor on the first power cap. I installed 270K resistors across the leads of each electrolytic cap according to the safety page on bottlehead. The power rating was 1W. I also upped the capacitance of the second and third power caps, but not the first (on which the bleeder blew). The capacitor still looks as though nothing bad happened to it. Another thing I was suspicious about is a cooling fan that is connected to wall power before the primary. Its specs are 115VAC, 130mA, 10W max. The 1 1/2 amp fuse before the PT primary is still fine.

I would just remove the bleeders and give it another shot, but I really don't want to blow up a cap or do any more damage. Any advice?

Miles Prower · 29th December 2007, 06:04 PM

Can you post a schemo of the power supply? It takes over 500Vdc to poof a 270K / 1W resistor. Are you sure it didn't just flash-over? That's a lot of voltage across one resistor.

Definitely don't remove the bleeders, and don't try again until this problem is sorted out.

tubewade · 29th December 2007, 08:51 PM

Is there any chance that the resistor that failed could have accidentally been something other than 270k ohms, perhaps 27K? I've done that before when the colour bands on different resistances were too similar to differentiate without actually measuring the resistance.

Just a thought from my own experience.

Jeb-D. · 29th December 2007, 09:09 PM

Quote:

Can you post a schemo of the power supply? It takes over 500Vdc to poof a 270K / 1W resistor. Are you sure it didn't just flash-over? That's a lot of voltage across one resistor.

Most commonly available resistors have a max working voltage rating of 350V. I know that means it's not really a 1W. It's a conspiracy with part manufactures I tell you. It is doubtful that kit uses more than 350V though.

Double check the values are right and that everything is stuffed in the right place. Also, make sure the caps are connected in proper polarity. Trace the traces to verify so. The S-5 kit I bought (was a k-502) had the silk screen backwards which caused me to blow the power supply caps.

fenpark15 · 30th December 2007, 12:58 AM

Here is the schematic. The resistors are indeed 270K 1W. C7 on the PCB is located right in line with C10 and C11, so I took it to be one of the power caps as well -- I put bleeders on all the electrolytics. The capacitors were in the correct polarity as well.

fenpark15 · 30th December 2007, 01:00 AM

Sorry that image is such poor quality. I had to reduce my scan way down for the site to let me post it.

Jeb-D. · 30th December 2007, 01:19 AM

Run it without the one that blew. All the caps will still discharge without it as long as you leave the other bleeders. It just may take a little more time to discharge the one without.

tubewade · 30th December 2007, 02:24 AM

I agree with Jeb. You already have a bleeder on the next cap and it will take care of discharging all of the capacitors. If the amp appears to work fine otherwise, run it that way.

fenpark15 · 30th December 2007, 04:19 PM

Now it's R26 (between the two 220uf electrolytics) and the bleeder on c11 that are going out. They are just getting dark and smoking as opposed to flaming instantly.

Jeb-D. · 30th December 2007, 06:17 PM

- Those caps that you increased in value, is the voltage rating at least the same as the originals?
-Make sure those electrolytics aren't in backwards.
-Try leaving the C7 bleeder only.
-What is the voltage rating on C7? That should give an idea of operating voltage for the circuit. Make sure the Max working voltage of the resistors your using for the bleeder are at least that value.
-After the brief power up with C7 bleeder only. Quickly feel the insulated part of the caps to see if their heating up. Only use one hand and be careful not to touch anything else, as the circuit may not be completely discharged by this time.
-Remember not to apply a signal without a load attached.

29th December 2007, 04:55 PM	#1
fenpark15 diyAudio Member Join Date: Dec 2007	Blown up resistor in S-5 amp kit... I just finished my s-5 k-16LS kit and plugged it in for my first ever tube experience. There was a loud pop and a bright light and that's it. I'm hoping someone can help me figure out what went wrong. The resistor that blew up was a bleeder resistor on the first power cap. I installed 270K resistors across the leads of each electrolytic cap according to the safety page on bottlehead. The power rating was 1W. I also upped the capacitance of the second and third power caps, but not the first (on which the bleeder blew). The capacitor still looks as though nothing bad happened to it. Another thing I was suspicious about is a cooling fan that is connected to wall power before the primary. Its specs are 115VAC, 130mA, 10W max. The 1 1/2 amp fuse before the PT primary is still fine. I would just remove the bleeders and give it another shot, but I really don't want to blow up a cap or do any more damage. Any advice?

29th December 2007, 06:04 PM	#2
Miles Prower diyAudio Member Join Date: May 2005 Location: USA Blog Entries: 2	Can you post a schemo of the power supply? It takes over 500Vdc to poof a 270K / 1W resistor. Are you sure it didn't just flash-over? That's a lot of voltage across one resistor. Definitely don't remove the bleeders, and don't try again until this problem is sorted out. __________________ There are no foxes in atheistholes www.dolphin-hsl.com

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Which resistor type for emitter resistor?	sajti	Parts	25	8th April 2009 06:12 AM
Possible blown amp	derrickg	Car Audio	0	11th April 2007 09:02 PM
blown sub	wharfrat	Subwoofers	10	23rd May 2004 05:12 PM
screen-plate resistor and grid leak resistor	metebalci	Tubes / Valves	4	26th February 2004 03:18 AM
ETI-480 sub amp blown :-(	Circlotron	Solid State	32	21st May 2003 03:54 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

29th December 2007, 08:51 PM	#3
tubewade diyAudio Member Join Date: Jun 2007	Is there any chance that the resistor that failed could have accidentally been something other than 270k ohms, perhaps 27K? I've done that before when the colour bands on different resistances were too similar to differentiate without actually measuring the resistance. Just a thought from my own experience.

30th December 2007, 01:00 AM	#6
fenpark15 diyAudio Member Join Date: Dec 2007	Sorry that image is such poor quality. I had to reduce my scan way down for the site to let me post it.

30th December 2007, 01:19 AM	#7
Jeb-D. diyAudio Member Join Date: Nov 2005 Location: SoCal	Run it without the one that blew. All the caps will still discharge without it as long as you leave the other bleeders. It just may take a little more time to discharge the one without.

30th December 2007, 02:24 AM	#8
tubewade diyAudio Member Join Date: Jun 2007	I agree with Jeb. You already have a bleeder on the next cap and it will take care of discharging all of the capacitors. If the amp appears to work fine otherwise, run it that way.

30th December 2007, 04:19 PM	#9
fenpark15 diyAudio Member Join Date: Dec 2007	Now it's R26 (between the two 220uf electrolytics) and the bleeder on c11 that are going out. They are just getting dark and smoking as opposed to flaming instantly.

30th December 2007, 06:17 PM	#10
Jeb-D. diyAudio Member Join Date: Nov 2005 Location: SoCal	- Those caps that you increased in value, is the voltage rating at least the same as the originals? -Make sure those electrolytics aren't in backwards. -Try leaving the C7 bleeder only. -What is the voltage rating on C7? That should give an idea of operating voltage for the circuit. Make sure the Max working voltage of the resistors your using for the bleeder are at least that value. -After the brief power up with C7 bleeder only. Quickly feel the insulated part of the caps to see if their heating up. Only use one hand and be careful not to touch anything else, as the circuit may not be completely discharged by this time. -Remember not to apply a signal without a load attached.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)