If you smell the burning on one of the coupling cap (upgrade caps and first turn on), would you replace or keep using? As I rememeber exactly, I smelled the burning but turned off/on couple times and it worked after that. I don't know if this is the reason causing the thump/pop.
The thump/pop is happen on the channel with the smell of burning cap. Now, it 's only happen when first turn on when it's cold. After playing for 15 mins or more after that, I tried to on/off again and doesn't happen. So I wonder if the caps is causing a thump.
I have searched on google but couldn't find any solution for the thump.
The thump/pop is happen on the channel with the smell of burning cap. Now, it 's only happen when first turn on when it's cold. After playing for 15 mins or more after that, I tried to on/off again and doesn't happen. So I wonder if the caps is causing a thump.
I have searched on google but couldn't find any solution for the thump.
As a "burning smell" is not normal, I'd suggest keeping the amp off until you know more. To Jean-Paul's point, here are some things to consider:
- A schematic would be helpful.
- You mentioned these are "upgrade" coupling caps. Are you certain they are of the correct type and voltage rating?
- Are these for interstage or for cathode coupling? It makes a difference.
Sorry Jean, I had another thread 2 weeks ago with the hum and finally got it figure out.
Hum with integrated tube amp
YaQin MC-100B commercial. Replaced 4 caps The original has 650v and I replaced with 800v
Only 1 cap smell but I checked again to make sure it's ok. So far no more smell and working fine. It has been working for a week now without any problem except thump when turn on. No thump after 15 mins using can be on/off without thump.
Hum with integrated tube amp
YaQin MC-100B commercial. Replaced 4 caps The original has 650v and I replaced with 800v
Only 1 cap smell but I checked again to make sure it's ok. So far no more smell and working fine. It has been working for a week now without any problem except thump when turn on. No thump after 15 mins using can be on/off without thump.
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This may be a silly question, but are you sure that the burning smell was coming from the capacitor itself? It would seem to be easier to believe that the replacement capacitor caused a problem that resulted in another component overheating. For example, if the capacitor had an insufficient working voltage, or if it was just leaky, it could cause an increased voltage on the grid of an output tube, thus causing increased conduction, leading to the overheating of the associated cathode resistor.
I have ordered couple caps extra last night, will swap it later to see what happen.
When I first fired it on, I can smell it and turned off right away, tried 2 more times and it's the same, put my nose to that caps, I could smell it but the cap still looked good. At first, I thought it was the tubes so I swapped different tube, then it worked. So I decided to try other tubes again, turned out it's working too, so I wasn't sure what happen even I still monitored the caps for couple days. Everything is fine except for the thump otherwise, the music is pretty good. And the cap doesn't smell anymore. That's the reason I don't know anywhere else's causing the problem.
I have rechecked everything last night and couldn't find anything so my last option is to replace the cap first when see what happen next. This is commercial build on PCB so it's kinda hard to replace the caps. That's why I am trying to see if anyone is encountered anything else before the last option.
When I first fired it on, I can smell it and turned off right away, tried 2 more times and it's the same, put my nose to that caps, I could smell it but the cap still looked good. At first, I thought it was the tubes so I swapped different tube, then it worked. So I decided to try other tubes again, turned out it's working too, so I wasn't sure what happen even I still monitored the caps for couple days. Everything is fine except for the thump otherwise, the music is pretty good. And the cap doesn't smell anymore. That's the reason I don't know anywhere else's causing the problem.
I have rechecked everything last night and couldn't find anything so my last option is to replace the cap first when see what happen next. This is commercial build on PCB so it's kinda hard to replace the caps. That's why I am trying to see if anyone is encountered anything else before the last option.
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First, when you turn a tube amp off you need to let it cool down before you turn it on again. If you were turning it off and on quickly that might have caused an arc somewhere which you're hearing as a thump.
Thumps are sometimes caused by arcing across the power switch. I've read that putting a cap across the switch will quiet the thump but I have no experience or expertise in this. Try searching and maybe you'll get more complete info.
Also, the schematic shows the coupling caps as 220nf which is 0.22uf, not 2.2uf. Not sure how that would affect the amp if you're using 2.2uf.
smell like burning rubber. I snipped with my nose around the cap, I was sure it's the one. However, the cap is still looking good, not a sign of blown or burn. If the cap is bad, does it still work with one tube since each channel has 2 tubes and 2 caps.
I don't have anything to measure the caps. I can check point to point compare with other caps.
I was turned on/off quickly after warm up so I didn't hear the thump again but if I wait for 10 mins later, then the thump happens when turn on.
At the moment: -The music comes out perfect, don't hear anything bad. Play 3-4hrs a day
-All 4 bias points set to 0.50v. I keep checking everyday and it's pretty much the same
I suspect there is a bit of confirmation bias happening here...
Look where those caps are - DC blocks o the grid of a valve, and with a high impedance bias control! It defies belief that there could be sufficient current through there to cause "burning smell" without:
- The valves arcing,
- R23/4 being on fire
- R20/22 catching fire
Does the channel in question still work, and are the bias voltages sensible?
Look where those caps are - DC blocks o the grid of a valve, and with a high impedance bias control! It defies belief that there could be sufficient current through there to cause "burning smell" without:
- The valves arcing,
- R23/4 being on fire
- R20/22 catching fire
Does the channel in question still work, and are the bias voltages sensible?
You might ask the manufacturer why it might smell when first powered up.
The purpose of the cap is to block DC voltage from the grid of the following tube. I sounds like you have a meter so all you have to do is set it to measure DC voltage and see if there is any on the grid.
You didn't say anything about the value of the caps you installed. As I pointed out, they should be 0.22uf not 2.2uf.
What value did you install? If they are 2.2uf that is waaay too large. Best to stick with stock values.
The purpose of the cap is to block DC voltage from the grid of the following tube. I sounds like you have a meter so all you have to do is set it to measure DC voltage and see if there is any on the grid.
You didn't say anything about the value of the caps you installed. As I pointed out, they should be 0.22uf not 2.2uf.
What value did you install? If they are 2.2uf that is waaay too large. Best to stick with stock values.
Not having to do with smell or not but these caps are highly overrated at 800V. What's the typical difference between cathode- and grid voltages here? 100V tops?
Jan
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