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Leben CS600 sound fading up and down

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Wondering if anyone has an idea what might be causing an issue with my Leben CS600.

While listening last night the sound faded away to nothing and then came back, it happened 2 or 3 more times randomly. Even the amount of time it was quiet varied.

I'm hoping it's a valve/tube issue as that easily replaced. The only tube issues I have had in the past (with other valve equipment, no issue with the Leben before this) have been obvious with crackling sounds audible with no music playing. Could this be the dumper tube designed to protect the other valves on startup? I'm thinking this because the sound is fading on both channels. Any other valve issue I would've thought would only relate to one side.

Are there any other possible causes anyone can think of e.g. Something overheating, transformer issue?

Anyone experienced the same symptom with a Leben or other valve based amp or a solid state amp for that matter? This weekend I'll role some tubes (probably won't get time until Sunday night) but I don't have a spare for the dumper tube.

Any help greatly appreciated. Thanks in advance.

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Sounds like a tube issue. Resit/swap or replace faulty tubes identified.

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I have a CS600 and I had a similar issue about a year and half ago just after I had purchased it, I had the same fading effect and then going to one channel and back to both, turns out it was just the Sub I had at time connected up the wrong way (by one connection I got wrong), after righting the problem , it has worked fine since and even better now that I don't have a Sub at all. However agree with the above also, it could be a valve issue, pays to check everything that's connected as well.

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Thanks guys. I have golden ear triton ones, which have powered subs which use dsp for the crossover to the mids and tweeters which the learn powers. But the connection is just plus and minus as per normal speakers. Sure if there was an issue with the electronics in a speaker I could imagine the whole speaker losing sound as the dsp wouldn't pass through the mids and treble. But I can't see how the would both fade down at the same time and back again even if both were faulty. Unless only having one speaker working then causes the amp to misbehave?!?!?

Speakers are quite new with plenty of warranty so I guess I can go back to my old pre and power amp and see if I get the same issue. Won't sound as good as my beloved Leben though. I'll also plug in a set of headphones to the Leben and flick over to the headphone section when it happens again and see if I still get sound.

If anyone has any other ideas, that would be much appreciated.

Cheers

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I've been using a CS600 for a few years and haven't experienced anything like fading. The only thing that comes to mind, which I guess is tube related are the settings (switches). Have you checked they're both positioned correctly?

SN

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Thanks everyone.  I have switched all the power valves and input valves, switches are correct.  Have gone back to old amp and I'm talking to sound labs group about getting servicing. 

 

Only tube I don't have a spare for is the 6CJ3 dumper tube.  Long shot but is there anyone in Melbourne (I'm in Northcote) with a spare or loanable 6CJ3?  There doesn't seem to be any for sale in Oz that I can find.

 

Cheers

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That tube you'd have to hunt for OS I'd say, I am not sure, but that tube is a NOS in the CS600 and of good quality,(and is the only tube I haven't replaced with NOS tubes) someone may correct me if I'm wrong, but Sound Labs should be able to supply another one? but that may cost or you could also try and contact Leben directly via Email and see what sort of 'take' they might have on the problem/ or suggest?. 

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