Bulldog Posted July 22, 2012 Posted July 22, 2012 Need some tube help, and probably my inexperience is going to clearly show. I've been getting a heavy, terrible, loud distorted sound from my Twin. When I slap the top of the amp, it stops for a while. I pulled off the back cover and watched the tubes as the distorted sound was happenng. I noticed that 2 of the 6L6GC's were "extremely" brite and glowing. Actually, the white Groove Tube lettering on both is burned looking. However, after hitting the top of the amp the distortion stopped and the tubes went back to a quiet glow. If you are looking at the amp from the back the burned looking tubes I'm describing are the 3rd and 4th from the left side of the amp. Looking at the amp from the back 6L6 tubes in the 1st and 2nd position look just fine. So, I've cleaned all tubes with contact cleaner with no difference. My guess is that one of the 3rd or 4th tubes are shot. Any thoughts are appreciated........
Steiner Posted July 22, 2012 Posted July 22, 2012 If the elements inside the tube are glowing red, the tube is bad. From your description, tubes 1&4 are in a set as are tubes 2&3. Replace all 4 tubes and save tubes 1 & 2 for the next time this happens.
DetroitBlues Posted July 22, 2012 Posted July 22, 2012 If the elements inside the tube are glowing red, the tube is bad. From your description, tubes 1&4 are in a set as are tubes 2&3. Replace all 4 tubes and save tubes 1 & 2 for the next time this happens. That is some great advice! Hope that is all your problem is. Best of luck!
Bulldog Posted July 22, 2012 Author Posted July 22, 2012 Thanks, will I need to have the amp bias changed with new tubes? Or, would this be a good time to experiment with new tube types. My guess is that if I stay with the same tubes no adjustments are necessary, right? Thanks for the info, appreciated.
Bulldog Posted July 22, 2012 Author Posted July 22, 2012 And, for now. Can I put the 2 good tubes in positions 1&4 and just run with less power?
kbp810 Posted July 22, 2012 Posted July 22, 2012 Yeah, that should work in the interim (I'm sure as you already know, as long as you keep one on each side), and can also help rule out that the problem is a tube and not something else internal. Keep a close eye on them when powering up again. As far as re-bias; the new set will likely be within a safe operating range, but It's still a good idea to have the bias checked and dialed in for the new set.
212Mavguy Posted July 22, 2012 Posted July 22, 2012 I would not rule out the amp in the list of suspects. These are not all that will made compared to the originals and perhaps there is a cold solder joint somewhere in the circuit's power section or power supply. That could allow for the behavior of the tubes and especially the "slap" factor.
212Mavguy Posted July 22, 2012 Posted July 22, 2012 ...tried to edit my post. couldn't. so sorry for the double. following the word "originals" should read "something not right in the power supply or power section. Most amp failures tend to happen in the power section" Cold solder joint is too specific and prone to inaccuracy, could also be an intermittent short. Maybe something is flopping around from the vibration and shorting stuff out. One time an amp of mine fresh out of the box from ebay with tube sockets on the pcb started really acting up, it was a long dead pill bug carcass wrapped in spider filaments rolling back and forth across the socket!
Bulldog Posted July 22, 2012 Author Posted July 22, 2012 Yeah, that should work in the interim (I'm sure as you already know, as long as you keep one on each side), and can also help rule out that the problem is a tube and not something else internal. Keep a close eye on them when powering up again. As far as re-bias; the new set will likely be within a safe operating range, but It's still a good idea to have the bias checked and dialed in for the new set. Thanks, so I'll put the 2 good tubes in positions# 1 & 4 leaving position's 2 & 3 open or empty until I get new tubes? I thinks that's what your saying - right. Sorry, I'm a little behind the curve when talking about electronics. ...tried to edit my post. couldn't. so sorry for the double. following the word "originals" should read "something not right in the power supply or power section. Most amp failures tend to happen in the power section" Cold solder joint is too specific and prone to inaccuracy, could also be an intermittent short. Maybe something is flopping around from the vibration and shorting stuff out. One time an amp of mine fresh out of the box from ebay with tube sockets on the pcb started really acting up, it was a long dead pill bug carcass wrapped in spider filaments rolling back and forth across the socket! You have to watch out for those pill bugs, they'll get you every time. We'll see what happens...... thanks for the insight.
Guest HRB853370 Posted July 22, 2012 Posted July 22, 2012 Good luck Bulldog, so far my TWRI has been just perfect, knock on wood.
Bulldog Posted July 22, 2012 Author Posted July 22, 2012 Good luck Bulldog, so far my TWRI has been just perfect, knock on wood. Thanks, I'm sure it'll be just fine....... KBP810 - Thanks, so I'll put the 2 good tubes in positions# 1 & 4 leaving position's 2 & 3 open or empty until I get new tubes? I thinks that's what your saying - right. Sorry, I'm a little behind the curve when talking about electronics.
kbp810 Posted July 23, 2012 Posted July 23, 2012 That's correct; but keep a close eye on them - if the problem was not with the tubes, but rather an internal issue, you'll see it happen again and will want to turn the amp off in short order and make an appointment with the doc.
Bulldog Posted July 23, 2012 Author Posted July 23, 2012 That's correct; but keep a close eye on them - if the problem was not with the tubes, but rather an internal issue, you'll see it happen again and will want to turn the amp off in short order and make an appointment with the doc. Got it, thanks man - appreciated!
ingeneri Posted July 28, 2012 Posted July 28, 2012 I had the same problem with my Fender DRRIna few years back. Turns out it was a short from the PCB board. Good luck.
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