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Old 19th August 2010, 12:43 AM   #1
ryc989 is offline ryc989  United States
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Question Tubelab SE blown C12

Hi,

Today my amp blew a fuse and I found that C12 had popped(fluid came out of capacitor). It appears that my rectifier tube was also damaged. I replaced both C12 and C22. I was able to power the amp up again with new output tubes. I am hearing some noise in the output of the channel where C12 blew, I am wondering what else I should check as the source of the noise?? The amp was dead quiet prior to the capacitor going bad and the other channel is still dead quiet. Any assistance would be greatly appreciated.

Regards,

Ralph
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Old 19th August 2010, 04:51 AM   #2
rknize is offline rknize  United States
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I assume you are talking about the Tubelab Simple SE (SSE) and not the Tubelab SE (TSE)? There are two reasons those caps might blow:

1) The cathode resistor R17/27 has failed or is intermittent. Are you doing any special with these (switchable bias, etc)? If the resistor opens the voltage across the cap will exceed maximum ratings.

2) The tube grid has somehow lost it's ground reference. This could put the tube into full conduction and the resulting plate current could cause the voltage across the cathode resistor to exceed the cap's rating.

Given that you said you lost your rectifier as well, I would say that #2 seems more likely to me. If the coupling cap (C11/21) is very leaky or shorting, the plate voltage of the 12AT7 would raise the output tube grid voltage in this way. That would also explain the noise.

Try swapping the coupling cap. Also check R15/25 and R16/26 to make sure they were not damaged, should the coupling cap be the culprit.
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Old 3rd September 2010, 08:46 PM   #3
ryc989 is offline ryc989  United States
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Hi Russ,

Thank you for you suggestions, I had to wait to get some new capacitors. I wound up replacing C11 & C21, R17 & R27, and R4(looked somewhat burnt, like it got real hot!). I checked all other resistors and they checked good. I also replaced all tubes and I am still running with the bridge rectifiers. I am still unsure what caused the issue so I do not wish to blow another rectifier tube. I do know I always leave the amp on, so it had been on for several months before I had this issue. I am wondering if that may have caused the problem to begin with. So far so good, I have been listening to the amp for 2 days and it seems to be ok, still worried about what actually caused the issue. I found another source of noise in the one channel to be a bad solder on the input RCA btw!! Once again thanks for taking time to help me.
Regards,
Ralph
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Old 3rd September 2010, 10:52 PM   #4
rknize is offline rknize  United States
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What are/were you using for C11/21? Another possibility is a short in the output tube itself, such as the screen touching the grid or something like that. Since you replaced everything, it's pretty likely you won't see the issue. Make sure you mark the tube that was in the socket at the time. If it wasn't the cause of the problem, it may have been damaged during the carnage.
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Old 4th September 2010, 01:44 AM   #5
ryc989 is offline ryc989  United States
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Hi Russ,

I was using Dynamicaps (I really thought the sound of these caps was excellent btw!!) which are rated to 630volts, I replaced them with Sonicap GEN I caps rated at 600volts. I believe my issue was with the tube also, but I replaced all the mentioned parts plus all the tubes just in case something was damaged. I do not think those caps were defective, but it will give me a chance to evaluate a different coupling capacitor(sound is definitely different). I am using this amp as an experiment of sorts, different tubes, coupling caps, output transformers to decide which suit my taste. Once again thank you for all the help.
Regards,
Ralph
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