[2359glenn]

Quote:

 
Thanks mate.
 
This morning I removed the metal cover that hides these resistors...and i can now tell that the 1K (5 watt) resistor is indeed burnt.
 
Attached pictures the middle resistor.
 

 
Cropped

 
I will try and replace this resistor today.
 
Anything else I should look into?
 
I am very thankful to all the help I am getting here.

After you do this repair
Do not reuse these tubes put in a new set of El34s

 

[Wolfbane]

I'd buy a tube tester. Nothing fancy or expensive is required. Jackson 648 and Eico 667 are two good testers for the money.
 
Wb

 

[BugleBoy]

Quote:

It's one good reason to own even a basic tube tester. You can't do "matching" with a basic emissions tester, but you can sure test for leaks or shorts! Better to do that in a tester than in an amp....

Thanks Skylab
 
I do have an emission tester which can test for shorts etc. I have been using these tubes for almost 6 months now and they tested fine when I first installed them. Also, in the past I could tell when the tube is getting to end of life; the music just starts to become...shall we say less musical!
 
But this this time the damage was sudden and catastrophic. Within 10 seconds the barbecue was well and truly on.
 
I am just glad that I was at home (and in close proximity to the amp) when this happened.

 

[BugleBoy]

Quote:

 
The right channel is closer to the main trafo. My Leben hums more on the right side, and Leben told me by email that this was the reason - which also makes sense if you look inside. 
 
It also makes sens that a bad tube caused this. A good reason to stay at home whenever you choose to let your tube amp be turned on. 

 
Quote:

I currently own a Leben CS600 and I used to own the CS300XS. Never picked up any hum on either channel. It sounds like Leben's QC is inconsistent.

 
I have always had small amounts of hum on the Leben which seems to disappear when i take the volume past 10 o clock. In addition, I have also observed the following:

• the amount of hum varies with the driver tubes i use (12ax7 / 5751 or 7729)
• the hum is more prominent with my speakers and high impedance headphones (HD600) and practically non-existent on low impedance headphones (fostex T50RP or Yamaha HP-1)

 

[BugleBoy]

Quote:

I've heard that it is especially bad in Australia.

 
Hmmm...wasn't aware of that.
 
Maybe I should invest in a line conditioner. Thoughts?

 

[2359glenn]

Quote:

 
Hmmm...wasn't aware of that.
 
Maybe I should invest in a line conditioner. Thoughts?

Don't waist your money!!!!!  .
The output transformer that is closer to the power transformer is picking up the 60Hz
magnetic field from the power transformer.
Even if you use a power conditioner the power transformer is still going to radiate 60Hz
and the output transformer will pick it up.

 

[Skylab]

Thanks Skylab

I do have an emission tester which can test for shorts etc. I have been using these tubes for almost 6 months now and they tested fine when I first installed them. Also, in the past I could tell when the tube is getting to end of life; the music just starts to become...shall we say less musical!

But this this time the damage was sudden and catastrophic. Within 10 seconds the barbecue was well and truly on.

I am just glad that I was at home (and in close proximity to the amp) when this happened.

Yeah, sometimes tubes just "go". I've had a tube arc and destroy a pair of DT990's. Its been rare in my extensive use of tubes, but it does happen. Sorry you had a case!

 

[BugleBoy]

MISSION ACCOMPLISHED!!!
 
After I replaced the 1K resistor the Leben is back to normal...singing beautifully. Also, an unintended, but pleasant, outcome of this repair work is that the HUM is gone....completely! i have never had my amp this quiet before...ever.
 
Big thanks to everyone for your inputs.
 
A special thanks must go to 2359glenn for highlighting the problem with such precision.
 
I have attached couple of pics of the fix.

 

 

[BugleBoy]

Quote:

Yeah, sometimes tubes just "go". I've had a tube arc and destroy a pair of DT990's. Its been rare in my extensive use of tubes, but it does happen. Sorry you had a case!

 
I have had the tubes pop suddenly before on other stuff...but never taking the equipment down with it.
 
I still wonder if the tube was the main culprit after all. Is it possible that the resistor got burnt and led to both right channel tubes failing in this manner? Just a theory

....

 

[2359glenn]

The tube that was in that socket caused the resistors to burn that killed the voltage to
the screen grids in the EL34s and killed the power to the driver tubes.
your hum could have been from this tube drawing to much screen current or
this tube was oscillating

 

[BugleBoy]

Quote:

The tube that was in that socket caused the resistors to burn that killed the voltage to
the screen grids in the EL34s and killed the power to the driver tubes.
your hum could have been from this tube drawing to much screen current or
this tube was oscillating

 
 
But the same set of tubes that used to hum before is not humming anymore. How can that be? I have swapped 3 set of tubes just to check...and they are all dead quite now. I have never known Leben to be this quite.

 

[2359glenn]

I don't know I really don't explanation on what happened to the hum
or these resistors were damaged in the past with a different set of tubes.
Anyway it is a good thing.

 

[BugleBoy]

Quote:

I don't know I really don't explanation on what happened to the hum
or these resistors were damaged in the past with a different set of tubes.
Anyway it is a good thing.

 
Yeah...it is a great outcome.  Thanks for you help.

 

[Skylab]

That's a great outcome indeed! Congrats

 

[Clayton SF]

I have come to believe that the next set of skills that I must acquire are the skills of soldering and desoldering. Following "Leben and The Case of the Burnt Resistors" has certainly piqued my interest in learning basic soldering skills.