Mark V Blows the fuse on standby

[tofisi]

Why blows the fuse on my MARK V on Standby? When I switch the power on my mark, the fuse blows out after one second. What could be wrong? Are possible power tubes or is this any other problem.

 

[JOEY B.]

Switch all 3 channrls to "diode rectifier" and see if it still happens. If it doesn't blow the fuse, get yourself a replacement 5U4GB tube. If the problem persits, I would take it back to the dealer and let them diagnose/fix it.

 

[tofisi]

Switch all 3 channrls to "diode rectifier" and see if it still happens. If it doesn't blow the fuse, get yourself a replacement 5U4GB tube. If the problem persits, I would take it back to the dealer and let them diagnose/fix it.

Shoud I set first two chanel to diode and third chanel to pentode? And it is imprtant how to set the switches on chanels 15,45 or 90 W?

 

[JOEY B.]

Switch all 3 channrls to "diode rectifier" and see if it still happens. If it doesn't blow the fuse, get yourself a replacement 5U4GB tube. If the problem persits, I would take it back to the dealer and let them diagnose/fix it.

Shoud I set first two chanel to diode and third chanel to pentode? And it is imprtant how to set the switches on chanels 15,45 or 90 W?

Channel 3 will not matter if it is pentode or triode, and the channels should be set to either 45 or 90 watts. The 10 watt setting will auto assign the rectifier tube (even on channel 3) regardless of what the mini toggle position is. At least that is how I interpreted the manual.
Good luck.

 

[JOEY B.]

Switch all 3 channrls to "diode rectifier" and see if it still happens. If it doesn't blow the fuse, get yourself a replacement 5U4GB tube. If the problem persits, I would take it back to the dealer and let them diagnose/fix it.

Shoud I set first two chanel to diode and third chanel to pentode? And it is imprtant how to set the switches on chanels 15,45 or 90 W?

Channel 3 will not matter if it is pentode or triode, and the channels should be set to either 45 or 90 watts. The 10 watt setting will auto assign the rectifier tube (even on channel 3) regardless of what the mini toggle position is. At least that is how I interpreted the manual.
Good luck.

 

[tofisi]

Switch all 3 channrls to "diode rectifier" and see if it still happens. If it doesn't blow the fuse, get yourself a replacement 5U4GB tube. If the problem persits, I would take it back to the dealer and let them diagnose/fix it.

Shoud I set first two chanel to diode and third chanel to pentode? And it is imprtant how to set the switches on chanels 15,45 or 90 W?

Channel 3 will not matter if it is pentode or triode, and the channels should be set to either 45 or 90 watts. The 10 watt setting will auto assign the rectifier tube (even on channel 3) regardless of what the mini toggle position is. At least that is how I interpreted the manual.
Good luck.

I was tryed that, but the fuse blows out again. I will take it back at the dealer.

thanks

 

[bpm91]

Don't forget to check the bias switch and which powertubes you have in there too. The Mark V shipped with 6L6s stock, but your bias switch may be incorrectly toggled to EL34s.

 

[tofisi]

Don't forget to check the bias switch and which powertubes you have in there too. The Mark V shipped with 6L6s stock, but your bias switch may be incorrectly toggled to EL34s.

It is set correct to 6L6

 

[thunda1216]

shorted rectifier tube. replace the rectifier tube. switching to silicon rectifier will not remove shorted tube from circuit (a short is a short...)

 

[fr0sty]

Look around back a the tubes when you switch off standby. My new markv had a bad tube. I played it for an hour before blowing a tube. Replaced the fuse, let it warm up and switch it from stand by. I was watching the tubes when I did that and saw one flashing. Quickly turned the amp off. After replacing that tube, it has been fine.

 

[tofisi]

Can I try replace the rectifier tube on MKV whith jj tube GZ 34 and see what happen?

 

[domct203]

If the JJ is a known good tube yes you can sub the GZ34 for the 5U4GB to see if the fuse will stop blowing.

shorted rectifier tube. replace the rectifier tube. switching to silicon rectifier will not remove shorted tube from circuit (a short is a short...)

This is correct. The 5U4GB is in parallel with the silicon diodes.

Channel 3 will not matter if it is pentode or triode, and the channels should be set to either 45 or 90 watts. The 10 watt setting will auto assign the rectifier tube (even on channel 3) regardless of what the mini toggle position is. At least that is how I interpreted the manual.
Good luck.

Once the amp is setup for silicon diode in all channels you could actually just remove the 5U4GB. If the fuse does not blow, replace the rectifier tube.

If you are sure that GZ34 is a good tube start there first.

Dom

 

[tofisi]

If the JJ is a known good tube yes you can sub the GZ34 for the 5U4GB to see if the fuse will stop blowing.

shorted rectifier tube. replace the rectifier tube. switching to silicon rectifier will not remove shorted tube from circuit (a short is a short...)

This is correct. The 5U4GB is in parallel with the silicon diodes.

Channel 3 will not matter if it is pentode or triode, and the channels should be set to either 45 or 90 watts. The 10 watt setting will auto assign the rectifier tube (even on channel 3) regardless of what the mini toggle position is. At least that is how I interpreted the manual.
Good luck.

Once the amp is setup for silicon diode in all channels you could actually just remove the 5U4GB. If the fuse does not blow, replace the rectifier tube.

If you are sure that GZ34 is a good tube start there first.

Dom

I was take out rectifier tube and Eureka the fuse no more blows out, than I was also try with GZ 34- fuse no more blows on Standbay. :mrgreen: :mrgreen: :mrgreen:

EJ domct203 You are my hero.

I have another question. Can I run amp without the rectifier tube?

 

[domct203]

The safest option would be to leave the GZ34 in there for now. If the amp gets accidentaly switched to 10W you'll be glad you did. Order a new 5U4GB. The dealer may warrenty the tube if the amp was just bought.

Dom

 

[tofisi]

The safest option would be to leave the GZ34 in there for now. If the amp gets accidentaly switched to 10W you'll be glad you did. Order a new 5U4GB. The dealer may warrenty the tube if the amp was just bought.

Dom

Thanks again.

 

[JOEY B.]

This is correct. The 5U4GB is in parallel with the silicon diodes.

Looking at the schematics for the MkV indicates that pins 4 and 6 of the 5U4GB are getting the high voltage from the power transformer regardless of the mini toggle position. The Dual Rectifier has the high voltage removed from these pins when in diode mode. I guess I learn something new every day. The good thing is that the MkV is up and running without too much money spent. The warranty for MESA preamp tubes is 6 months, maybe the same for rectifier tubes.

http://www.schematicheaven.com/boogieamps/boogie_dualrectifier.pdf

http://forum.grailtone.com/viewtopic.php?f=33&t=39690