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The Leben CS300XS Thread - Page 115

post #1711 of 2118

I thought the Lebens were built with 2 different resistors levels and that's why people had different experience with the headphone performance.  Search back in this thread for a discussion on this.

post #1712 of 2118

The 100 ohm resistor was added to the screen grid as grid stoppers

if this resistor burned I would get rid of the tube that was in that socket.

And the 1000 ohm resistor in the power supply is burned up. Get a ohm

meter and check it. I think it is on top of the chassis to reduce heat under the chassis.

post #1713 of 2118
Quote:
Originally Posted by 2359glenn View Post

The 100 ohm resistor was added to the screen grid as grid stoppers

if this resistor burned I would get rid of the tube that was in that socket.

And the 1000 ohm resistor in the power supply is burned up. Get a ohm

meter and check it. I think it is on top of the chassis to reduce heat under the chassis.

 

Thanks 2359glenn

 

There is a 1K resistor on the top of the chassis. Visually it looks fine. I will check with an ohm meter tomorrow and report back.

 

They look like the ceremic cement power resistors. Does anyone know what brand?

post #1714 of 2118

Boy, that's scary. I wonder what would cause those resistors to burn up. If it is also the 1KΩ resistor.

post #1715 of 2118
Quote:
Originally Posted by Clayton SF View Post

Boy, that's scary. I wonder what would cause those resistors to burn up. If it is also the 1KΩ resistor.

 

I am unsure what could cause such failure.

 

From the outside it seemed like the tubes got damaged and set off a chain reaction...but it could just as well be the other way round.

 

Historically the right channel tubes have worn out more often on my amp.

post #1716 of 2118
Quote:
Originally Posted by BugleBoy View Post

 

Thanks 2359glenn

 

There is a 1K resistor on the top of the chassis. Visually it looks fine. I will check with an ohm meter tomorrow and report back.

 

They look like the ceramic cement power resistors. Does anyone know what brand?

The one on the capacitor underneath is just a cheep Chinese resistor

No audio goes through these resistors it is just important that you get the

same wattage.

 

And it was a bad tube that caused this !!

post #1717 of 2118
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....
post #1718 of 2118
Quote:
Originally Posted by Skylab View Post

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....


I am wondering, though: would a tube tester have been able to pick out that bad tube before it went south? It sounds like that tube had been running perfectly for some time in his amp before it went kablooie.

post #1719 of 2118

Another problem with tube testers is they don't test the tubes

at the same voltages they will be run at in the amp.

But they will indicate if a new tube has a outright short before

you put it in your amp.

post #1720 of 2118
Right - the tester might not have caught it...but look at it the other way...if you only want a tester to check for leaks and shorts, you can buy a decent vintage emissions tester on eBay for $100 or less. Cheaper than many of the tubes we all use. As long as you aren't asking the tester to give you precise mutual transconductance numbers, you don't need a big expensive tester.
post #1721 of 2118
Quote:
Originally Posted by BugleBoy View Post

 

I am unsure what could cause such failure.

 

From the outside it seemed like the tubes got damaged and set off a chain reaction...but it could just as well be the other way round.

 

Historically the right channel tubes have worn out more often on my amp.

 

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. 

post #1722 of 2118

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.

post #1723 of 2118
Quote:
Originally Posted by Clayton SF View Post

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.

 

Nah. It's a mains issue. Variations like this is known across producers. I have crappy mains I guess. 

 

And it is especially so with products designed in countries with different mains voltage, like using american or Japanese stuff in Europe (where I am). They do not have access to real 230 mains in US or Japan, they use step up transformers. So that's why they don't necessarily pick up the real world mains issues in 230V-land. 


Edited by ardilla - 5/10/13 at 3:26pm
post #1724 of 2118
Quote:
Originally Posted by ardilla View Post

Nah. It's a mains issue. Variations like this is known across producers. I have crappy mains I guess. 

And it is especially so with products designed in countries with different mains voltage, like using american or Japanese stuff in Europe (where I am). They do not have access to real 230 mains in US or Japan, they use step up transformers. So that's why they don't necessarily pick up the real world mains issues in 230V-land. 

I've heard that it is especially bad in Australia.
post #1725 of 2118
Quote:
Originally Posted by 2359glenn View Post

The one on the capacitor underneath is just a cheep Chinese resistor

No audio goes through these resistors it is just important that you get the

same wattage.

 

And it was a bad tube that caused this !!

 

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.

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