[BugleBoy]

This morning when i switched on the Leben I heard 2 popping sounds within 10 Seconds with smoke starting to come up from underneath the amp. I immediately switched off the Leben and tested the tubes...both tubes on the right channel were dead with the left channel still testing strong. (The right channel tubes have always worn out a lot quicker than the left channel on my Leben...not sure why?)
 
I then started investigating any other signs of damage. Underneath the amp I found a burnt resistor...100ohm I think. Other than that I could not find any visible signs of damage. Is there anything else i should be looking for?
 
I have attached a couple of image for reference. The resistor below the "BLOWN RESISTOR" text is the only one that seems to have been damaged.
 

 

 
Before I proceed with the repairs I have a few questions. I am keen to get inputs / insights from the head-fi community.
 

• Can anyone tell what brand of resistors (blue ones) are used in the Leben CS300X? Where can I buy them online?
• What is the wattage of the damaged resistor?
• Looking at the corresponding resistor on the left channel looks like the blown resistor is 100ohm 1% tolerance. Can anyone confirm this?
• If I cannot find the same resistors; what are the good or better alternatives?
• Given that the right channel tubes wear out quickly on my Leben; are there any other problems that I should be looking into?
• Any other thoughts or suggestions?

 
Look forward to your responses.
 
Thanks

 

[PredatorZ]

The resistors look like Riken RMG “Metal Film”. I would have the tube that's on that circuit tested, it might be arcing or shorting out and that resistor acted as a fuse. Or some other part up line is passing to much current.  Looks like the same part as this ...   http://www.ebay.com/itm/Riken-Ohm-Resistor-100K-1-Watt-1-New-Tube-Guitar-HiFi-Stereo-Amplifier-Part-/151019776794?pt=Vintage_Electronics_R2&hash=item23297aeb1a    but its hard to see the colors exactly in your photos.
 

 

[PredatorZ]

I had a question about noise, with an open topography, all those wires and no circuit board with a well designed ground plane, do you get noise or hiss at higher volume, or just with headphones in general ? It looks very DIY when you open it up, Ive seen other hand built tube amps like that, but even more random and messy. I read the 6Moons review of it, but I think he was only using speakers, unless I missed that part.
 

 

[BugleBoy]

Quote:

The resistors look like Riken RMG “Metal Film”. I would have the tube that's on that circuit tested, it might be arcing or shorting out and that resistor acted as a fuse. Or some other part up line is passing to much current.  Looks like the same part as this ...   http://www.ebay.com/itm/Riken-Ohm-Resistor-100K-1-Watt-1-New-Tube-Guitar-HiFi-Stereo-Amplifier-Part-/151019776794?pt=Vintage_Electronics_R2&hash=item23297aeb1a    but its hard to see the colors exactly in your photos.
 

 
Thanks Predetor...Indeed it is the Riken resistors.
 
The color sequence on the resistor is 'Brown - Black - Brown - Brown' which translates to 100ohms. I checked the values on this site http://samstechlib.com/24614782/en/read/4_Band_Resistor_Color_Codes
 
I have attached another photo i took a year ago.

 
I also tried to look up the resistor values on the CS300X schematics but could not find the 100ohm connected to the tube. attached the schematics.

 

[BugleBoy]

Quote:

I had a question about noise, with an open topography, all those wires and no circuit board with a well designed ground plane, do you get noise or hiss at higher volume, or just with headphones in general ? It looks very DIY when you open it up, Ive seen other hand built tube amps like that, but even more random and messy. I read the 6Moons review of it, but I think he was only using speakers, unless I missed that part.
 

 
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)

 

[PredatorZ]

Hey Bugleboy
 
I'd give Leben a call, or email, see if you can talk to one of they're techs, see if they have seen this before. I bet its a common problem, most likely a diode or cap is bad, so you have an un-regulated voltage. It's a chain reaction once a part like that goes.
   If you notice, the electrolytic Caps have a little X in the tops, that is a strain relief, when the part starts going bad, you will see the top expand upwards, making it a little rounded, it's an easy way to do a quick visual inspection of caps, they should be nice and flat on top.  Diodes control the direction of flow, if one goes bad, voltages are getting to the wrong parts, also not good. As you have probably know by now, the worst smell is when a part fries and a little puff of smoke comes out of your amp, it really stinks, metaphorically and literally. Good luck fixing it. I'm guessing you have some soldering skills ? If not you can always ask for pointers, or find a local tech who can fix her for you. 

 

[BugleBoy]

Quote:

Hey Bugleboy
 
I'd give Leben a call, or email, see if you can talk to one of they're techs, see if they have seen this before. I bet its a common problem, most likely a diode or cap is bad, so you have an un-regulated voltage. It's a chain reaction once a part like that goes.
   If you notice, the electrolytic Caps have a little X in the tops, that is a strain relief, when the part starts going bad, you will see the top expand upwards, making it a little rounded, it's an easy way to do a quick visual inspection of caps, they should be nice and flat on top.  Diodes control the direction of flow, if one goes bad, voltages are getting to the wrong parts, also not good. As you have probably know by now, the worst smell is when a part fries and a little puff of smoke comes out of your amp, it really stinks, metaphorically and literally. Good luck fixing it. I'm guessing you have some soldering skills ? If not you can always ask for pointers, or find a local tech who can fix her for you. 

 
Thanks Predator.
 
Yes I will email Leben today...hope they are responsive!
 
I checked all the caps...and they are all flat on the top. None of the Caps look abnormal...visually. The Elna Capacitors are easy to buy...so may be an idea to replace them all!
 
Regarding the smell and the smoke; that is exactly what happened. It was a sinking feeling when I heard two popping sounds 10 meters away...by the time I got to the amp the barbecue had already started
 
I agree with you that the problem may lie elsewhere...not necessarily with the resistor that got fried.
 
cheers