Hello,
I built the tubelab SE earlier this year. It's been working perfectly for the past 6 months.
Yesterday I turned it on and sparks flew around inside the rectifier. The 5ar4 rattles now, so I guess the filament is broken.
I had an old 5ar4 sitting around. I have no idea if it is good or not, but i plugged it in (after checking the circuit for obvious shorts or other problems) and powered it up.
This time r5 almost instantly turned bright red, and r6 shows signs of being hot.
So, I've checked again, and I do not see any visual signs of any other components having failed, and i don't see any shorts anywhere.
I'll attach the power supply schematic, and here's a link to the full schematic, if it helps anyone to help me. The components I've marked in red on the power supply schematic are the ones which have visibly failed.
http://www.tubelab.com/AssemblyManualTubelabSE/Schematics_TSE.htm
Please let me know if you have any ideas as to what would cause these components to fail all of a sudden!
Thank you very much! I'm already in emotional pain from not having any music to listen to today!!
I built the tubelab SE earlier this year. It's been working perfectly for the past 6 months.
Yesterday I turned it on and sparks flew around inside the rectifier. The 5ar4 rattles now, so I guess the filament is broken.
I had an old 5ar4 sitting around. I have no idea if it is good or not, but i plugged it in (after checking the circuit for obvious shorts or other problems) and powered it up.
This time r5 almost instantly turned bright red, and r6 shows signs of being hot.
So, I've checked again, and I do not see any visual signs of any other components having failed, and i don't see any shorts anywhere.
I'll attach the power supply schematic, and here's a link to the full schematic, if it helps anyone to help me. The components I've marked in red on the power supply schematic are the ones which have visibly failed.
http://www.tubelab.com/AssemblyManualTubelabSE/Schematics_TSE.htm
Please let me know if you have any ideas as to what would cause these components to fail all of a sudden!
Thank you very much! I'm already in emotional pain from not having any music to listen to today!!
Attachments
Depending on the quality of 5AR4, it has been known to arc inside. I have a restored Dynaco ST-70 which had that happened twice and when it did, the fuse blew. Both were cheap 5AR4 (Ruby and Sovtek). Besides making sure your 5AR4 is in good condition or replacing it, you may also want to make sure the power caps are ok as well.
Let me tell you a couple of other things I've tried, and then ask a stupid question...
1st, I tested the transformer, and it tested OK
Then, I replaced the resistors, re-connected the power transformer, and applied power w/ no tubes.
Now the transformer makes an audible hum! (Not when it's disconnected, but when it is in the circuit)
So, let me know if that gives you any new clues.
( have my suspicions about those freed diodes.. only because if the resistor directly in front of them had enough current to glow red, would all that power be going through those little silicon diodes, too? I don't know how much they can take... they don't smell like blue smoke, and they still look OK)
Then on to my stupid question.....
Is there a way to test a capacitor w/ a cheap multi-meter? (no cap. test setting)
I did check for an internal short, and the caps aren't. And, i did use higher voltage caps from the start... They didn't even fit on the PCB, so I had to use short jumper wires to connect them.
But, if there's another way to test a cap, please let me know!
This was a cheap 5ar4 that blew originally.. (sovtek) But.. now that the transformer hums w/ no tubes, either something else caused the problem, or the 5ar4 took out some other components when it died.
I wish I could do some more troubleshooting on my own, but unfortunately, I don't have any extra components. I guess I'll wait for a little more advice from you guys, then order some parts so I can start testing.
Thanks for getting back to me so soon!
1st, I tested the transformer, and it tested OK
Then, I replaced the resistors, re-connected the power transformer, and applied power w/ no tubes.
Now the transformer makes an audible hum! (Not when it's disconnected, but when it is in the circuit)
So, let me know if that gives you any new clues.
( have my suspicions about those freed diodes.. only because if the resistor directly in front of them had enough current to glow red, would all that power be going through those little silicon diodes, too? I don't know how much they can take... they don't smell like blue smoke, and they still look OK)
Then on to my stupid question.....
Is there a way to test a capacitor w/ a cheap multi-meter? (no cap. test setting)
I did check for an internal short, and the caps aren't. And, i did use higher voltage caps from the start... They didn't even fit on the PCB, so I had to use short jumper wires to connect them.
But, if there's another way to test a cap, please let me know!
This was a cheap 5ar4 that blew originally.. (sovtek) But.. now that the transformer hums w/ no tubes, either something else caused the problem, or the 5ar4 took out some other components when it died.
I wish I could do some more troubleshooting on my own, but unfortunately, I don't have any extra components. I guess I'll wait for a little more advice from you guys, then order some parts so I can start testing.
Thanks for getting back to me so soon!
When R5 gets red hot, it is from excess current flowing through it. The only way I see this happening is a short somewhere down stream from it. The PT humming also points to a short somewhere.
The resistor will probably destroy itself before the diodes are damaged.
I have never tried to check a capacitor on a DVM. When I think one is suspect, I toss it in the trash, so I don't have any failed caps to try to measure. Sometimes they are fine at lower voltages, such as what a DVM might apply, but break down catastrophically at higher voltages.
There is almost always a lot of collateral damage around a failed electrolytic capacitor. When in doubt, I just replace them.
Win W5JAG
The resistor will probably destroy itself before the diodes are damaged.
I have never tried to check a capacitor on a DVM. When I think one is suspect, I toss it in the trash, so I don't have any failed caps to try to measure. Sometimes they are fine at lower voltages, such as what a DVM might apply, but break down catastrophically at higher voltages.
There is almost always a lot of collateral damage around a failed electrolytic capacitor. When in doubt, I just replace them.
Win W5JAG
I'm not sure about the cause of PT hum but FRED diode problems I've had recently. When mine went bad the fuse (250V 2A slo-blow) blew right away. I replaced the diodes with Fairchild "Stealth" mentioned in this thread. I'll see how it holds up.wicked1 said:
As for 5AR4, I heard that once it arcs, likely it's done. You may want to get a new one just to make sure. I have JJ brand and they are not that expensive. Is it really good like RCA and Mullard? No, but I think they are better than Sovtek.
OK,
New diodes, new capacitors, new rectifier tube... Back in business.
I think the caps were ok, but better safe than sorry. My guess is that either the diode or the tube failed, and took the other one out w/ it.
I used the fairchild "stealth" diodes that were mentioned in the previous post.
New diodes, new capacitors, new rectifier tube... Back in business.
I think the caps were ok, but better safe than sorry. My guess is that either the diode or the tube failed, and took the other one out w/ it.
I used the fairchild "stealth" diodes that were mentioned in the previous post.
Mine is still dead silent. (as far as my ears can tell)
I actually think it sounds better than ever, but that's just because I've been listening to an inferior amp for the past week.
(tho I did re-bias, and am using a different brand rectifier, but I doubt I can tell a real difference from that)
I actually think it sounds better than ever, but that's just because I've been listening to an inferior amp for the past week.
(tho I did re-bias, and am using a different brand rectifier, but I doubt I can tell a real difference from that)
One thing that seems to help the current crop of 5AR4 is to put a high voltage silicon diode in series with each plate. I generally use something like the UF4007. This prevents arcing during warm up and under most transient conditions, it effectively increases the PIV rating of the rectifier by close to the rating of the diodes used. (depends on diode reverse leakage current) It basically prevents the rectifier from seeing much of the pk inverse voltage it would normally see on the non-conducting plate. I have had relatively few failures with 5AR4 since I started doing this and it does not otherwise impact the performance of the tube rectifier.
Hello,
I fixed my amp, and now it has done it again. I didn't have a fuse on the amp before, and now I do, so at the moment the 5ar4 arced, the fuse blew.
The problem is... when the amp started to fail last time, I could quickly see which parts were overheating.
Now I don't know how to track down the problem.
One thing it could be.. after the last time, r5 darkened. I tested it, and it was still at 270 ohms, so I left it. Now, r5 is completely dead. Would the negative supply rail failing cause the 5ar4 to fail? Or maybe its just that when whatever failed on the amp, r5 heated up again and burned out before the fuse blew.
(there's a link to the schematics on the first post)
This time both diodes are still OK. The caps (c6 and c7)are ok, as far as I can test, but I don't really know. They tested ok last time too, but I replaced them anyway.
One last thing, after the 5ar4 died this time, I thought maybe it was just a bad tube, so I replaced it. The amp powered up, sounded pretty distorted for a minute, and as I was walking over to check it out, the new 5ar4 arced and died.
So.. let me know if anyone has any ideas what could be wrong.... again.....
thanks!
Oh, KevinKr, I did not put diodes on the plates of the rectifier. I was just looking at the board, and I can cut a couple of traces and do that. But seeing as how 3 have died now, its not the tube failing first, but something else causing it to arc.
I fixed my amp, and now it has done it again. I didn't have a fuse on the amp before, and now I do, so at the moment the 5ar4 arced, the fuse blew.
The problem is... when the amp started to fail last time, I could quickly see which parts were overheating.
Now I don't know how to track down the problem.
One thing it could be.. after the last time, r5 darkened. I tested it, and it was still at 270 ohms, so I left it. Now, r5 is completely dead. Would the negative supply rail failing cause the 5ar4 to fail? Or maybe its just that when whatever failed on the amp, r5 heated up again and burned out before the fuse blew.
(there's a link to the schematics on the first post)
This time both diodes are still OK. The caps (c6 and c7)are ok, as far as I can test, but I don't really know. They tested ok last time too, but I replaced them anyway.
One last thing, after the 5ar4 died this time, I thought maybe it was just a bad tube, so I replaced it. The amp powered up, sounded pretty distorted for a minute, and as I was walking over to check it out, the new 5ar4 arced and died.
So.. let me know if anyone has any ideas what could be wrong.... again.....
thanks!
Oh, KevinKr, I did not put diodes on the plates of the rectifier. I was just looking at the board, and I can cut a couple of traces and do that. But seeing as how 3 have died now, its not the tube failing first, but something else causing it to arc.
Didn't someone else here have essentially the same problem? I'll search around and see if I can find a related thread...
Edit: here it is, except the board in question was a Simple SE, not a Tubelab SE. Might still be some useful info, though...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=131317
Edit: here it is, except the board in question was a Simple SE, not a Tubelab SE. Might still be some useful info, though...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=131317
wicked1 said:
I'm going back and reading your thread more carefully. The Tubelab SE is a fixed bias design. I don't have one myself; I have a Simple SE. The Simple SE uses a different bias strategy.
Judging by the schematic, I'd expect if you lost the negative supply rail you would also lose the negative bias voltage on the output tubes. They would go into full conduction at this point. Current draw on the 5AR4 would be enormous - I doubt it would last long under those conditions. When it finally arcs and dies it I wonder if it might take C4 with it.
If you power up a fixed bias amp with no negative bias voltage it would sound very bad indeed. Since the tubes are pushed all the way over to full conduction it is unlikely they are operating in their "most linear" region. Not to mention it's mighty hard on the output tubes (red plate) and absolute murder on the rectifier tube.
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