[Will2]

Hi,

I have a pair of Bella Extreme 100 Platinum series amps and was hearing a sound like wind blowing through my right channel so I switched the tubes and the sound mover to the left channel - so now I know it is the tubes.  The configuration is:

KT88                  KT88
   6SN7  6SL7  6SN7
KT88                  KT88

How do I go about identifying which tube is at fault?

Cheers
Will

[toobluvr]

You need to determine if it is the KT88 or the 6SN7, so you need to move them independently.

First, simply flip-flop the two outside 6SN7 tubes.  If noise follows the tube, you have found it.  If not, they are fine.  Move onto the KT88.

Reverse only two at a time, not all four.  Flip-flop two rear ones.  If the noise follows the tube you have found it.  If not, the front KT88 on the noisey side is the culprit.  Confirm this by reversing the front ones.  The noise will follow the bad one.

Obviously, this test assumes the left KT88 pair are for left channel and right KT88 pair are for right channel.

Before moving any power tubes, you should reduce bias on all, just to be safe.   It is not critical to have correct bias for this test.  Low is safe and will tell you what you need to know.

Good Luck!   

[Bill Baker]

Hello Will,
 If you still have the Quick Start manual that came with the amps, the procedure for setting up the amps will also help you determine and find a noisy tube. If you don't have the manual, send me an email and I will email you the link.

As toobluvr mentioned, starting with the 6SN7s and the 6SL7 fisrt will be the easiest way to eliminate these first. Switch one at a time between the two amps. You do not have to rebias when swapping these tubes.

[toobluvr]

Ooops....sorry.   I thought it was a stereo amp, so was giving advise based on that!   

For monoblocks, the logic and approach is similar.  Just reverse one tube at a time across the monos till the noise moves to the other channel.  When that happens, you have found the bad tube.

[toobluvr]

Actually, let me modify that.

First reverse all three of the 6S** tubes across the monos.  If the noise moves, one of the three is faulty.   Now start reversing them across monos one at a time to identify the exact one.

If noise doesn't move, the problem is one of the KT88.  Switch them across the mono amps in pairs.  When the problem moves with the tube, you know it is one of those two.   Now just swap then one at a time across monos to find the culprit.

I think this will be the fewest number of steps, and on/off cycles for your amp.

[Will2]

Thanks so much guys ..... I'll start the process tonight after I get the kids to bed and let you know what I find.  It might take a while .... these tubes get really hot.  Am I right in thinking that I keep the preamp on throughout the process and just turn the monos off/on between each stage of the process?  I don't want to damage the amps while I'm at it.  Right now I power up: Source - pre- amps and power down in reverse.  I'm assuming powering the amps down then up again after a tube swap won't damage anything.

[toobluvr]

Will.....

It is safe to leave all other gear on during the process.  Just turn amps on and off during the tube swaps.   I find a winter glove helpful for pulling the hot tubes.  As you can tell, I'm a veteran of this sort of diagnostics.   

Be methodical and keep track of what you're doing and you'll find the problem in no time.   

[Will2]

Go figure ...... I swapped the 6S**'s between monos again and now - no wind-blowing sound - simple silence .  I can only guess it is one of the 6S**'s that is starting to go but was "shaken back to life" in the swap.  If it starts to play up again I know where to focus my attention. 

By the way, if it starts happening again is it dangerous to keep running the amps?  I live in Bermuda and it takes weeks to get anything here.  Would hate to go weeks without the amps ..... if it's dangerous to run the maybe I should order some replacement tubes in the meanwhile.

[toobluvr]

Not necessarily.   Maybe in the process of unseating and seating tubes you simply made a better pin connection.   Or maybe it only happens when amps are fully warmed up and tubes good and hot.   Lots of different possibilities.

If it is simply a noisey tube, chances are no harm can come to amps.  Bill can better answer that.

It is always a good idea to have some backup tubes on hand.   Obviously they get you back to music faster, but they are also handy in diagnosing things.

[Bill Baker]

It could be a dirty or loose contact in the socket. If they are remain quiet, no worries. As mentioned, having a few extra tubes around is always a good idea. Think of a tube like a light build, you never know when one is going to go out on you.

For testing, I would leave all the other gear off. You will be installing the power tubes while the amp is on. (input/driver tubes already installed).
Here is a quick link to the start up. If you have any further questions, let me know.
http://www.bellaextreme.com/bella100manual.htm

[Will2]

Thanks for your help John and Bill ..... the culprit has been identified and banished!! 

[Bill Baker]

Very glad to here this Will. So what was the final culprit?

[toobluvr]

 

[Will2]

The front left GE 6550.  There was corrosion on the base - not sure if that was what did it, but the other tubes don't have that.  I'm hoping it's not due to the humid/salty air here in Bermuda.  If it is I'm in for an expensive time with all my tubes 

[toobluvr]

Are we supposed to feel sorry for ya, Mr. Bermuda lifestyle!