Mark V wont turn on. tried to replace Power tubes.
- Thread starter thediavlo
- Start date
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Wayno
Well-known member
thediavlo said:
Have you accidentally got the rectifier tube and a power tube mixed. Unlikely but has been known to happen?
Wayno
Well-known member
Sorry but only thing I can think of is maybe one of the new tubes is bad. Have you still got the old tubes to try putting back in? That would eliminate a problem else where if they work correctly. Short of that probably a job for a tech if you're not up to working on the insides yourself. Sorry can't be of more help.
Did you replace the Rectifier tube? if the answer is yes, it may have a short. If the answer is no, you may have a short. if the amp would not power up and no lights on the panels or footswitch, the replaced fuse probably opened the second you turned on the power to the amp.
You should not have to remove the chassis as this can be a common problem with the Rectifier tube. I would say there is a slim chance the issue is internal but cannot rule that out.
+1 on the old tubes, go back to square one to verify if rectifier tube or new tube is culprit....
if you still have the old tubes, did you experience any fuse issues? If not, I would start there, remove the new tubes and install the old power tubes. At the same time remove the 5U4GB rectifier tube. Set the power switch on each channel to 90W setting. Change the fuse if blown, verify you have a speaker connected to one of the output jacks, and most important, confirm that the bias switch is in the correct position for the power tubes in use, and then turn on the amp. Let it warm up a bit longer if the fuse does not go on you since the parallel path provided by the Rectifier tube is not there. Check to see if the power tube heaters are glowing at about the same intensity. If one appears very dark (may a dim orange glow) it may be possible one tube has a crack in the glass and could also have other internal damage (this is assuming you did not take out the new tubes).
If the fuse does not go immediately after taking the amp out of stand by you found the problem as it is the Rectifier tube. I have already had new ones do this on me too. If the fuse does go.... you have a short in one of the power tubes. Also note: if a screen resistor had opened up as a result of failed power tube, there will be no sound or extremely degraded tone but the change of maintain the fuse without blowing it will be slim. Also if you had a bad rectifier tube, it will blow the fuse once you turn on the power switch as it is part of the active circuit in stand by mode.
If all is good, power down and install the new power tubes. This time you will watch the tubes when you turn it on. Once the amp is taken out of standby (keep your hand on the standby switch or the power switch if needed to shut the amp down quickly) verify the power tubes do not saturate and run into overload (red plate) after taking the amp out of stand by. If you have a bad power tube, the may happen. If all is good and you get that familiar blue hue (depends on tubes) you should at least hear any white noise or typical amp noise. Note: I personally would not operate the amp for any extended period of time without the Rectifier tube. Even though it may appear out of the current path it is operating in parallel to the silicon diodes, the limitations would be the larger voltage drop across the tube rectifier so in essence it is not supplying current as the diodes would have a lower voltage drop than the tube.
You should not have to remove the chassis as this can be a common problem with the Rectifier tube. I would say there is a slim chance the issue is internal but cannot rule that out.
+1 on the old tubes, go back to square one to verify if rectifier tube or new tube is culprit....
if you still have the old tubes, did you experience any fuse issues? If not, I would start there, remove the new tubes and install the old power tubes. At the same time remove the 5U4GB rectifier tube. Set the power switch on each channel to 90W setting. Change the fuse if blown, verify you have a speaker connected to one of the output jacks, and most important, confirm that the bias switch is in the correct position for the power tubes in use, and then turn on the amp. Let it warm up a bit longer if the fuse does not go on you since the parallel path provided by the Rectifier tube is not there. Check to see if the power tube heaters are glowing at about the same intensity. If one appears very dark (may a dim orange glow) it may be possible one tube has a crack in the glass and could also have other internal damage (this is assuming you did not take out the new tubes).
If the fuse does not go immediately after taking the amp out of stand by you found the problem as it is the Rectifier tube. I have already had new ones do this on me too. If the fuse does go.... you have a short in one of the power tubes. Also note: if a screen resistor had opened up as a result of failed power tube, there will be no sound or extremely degraded tone but the change of maintain the fuse without blowing it will be slim. Also if you had a bad rectifier tube, it will blow the fuse once you turn on the power switch as it is part of the active circuit in stand by mode.
If all is good, power down and install the new power tubes. This time you will watch the tubes when you turn it on. Once the amp is taken out of standby (keep your hand on the standby switch or the power switch if needed to shut the amp down quickly) verify the power tubes do not saturate and run into overload (red plate) after taking the amp out of stand by. If you have a bad power tube, the may happen. If all is good and you get that familiar blue hue (depends on tubes) you should at least hear any white noise or typical amp noise. Note: I personally would not operate the amp for any extended period of time without the Rectifier tube. Even though it may appear out of the current path it is operating in parallel to the silicon diodes, the limitations would be the larger voltage drop across the tube rectifier so in essence it is not supplying current as the diodes would have a lower voltage drop than the tube.
Wayno
Well-known member
Great news, rock on.
