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AUDIO FORUMS >> General Discussion and Support >> New KT66 Failing?
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Message started by ScottNC on 12/04/18 at 01:24:48

Title: New KT66 Failing?
Post by ScottNC on 12/04/18 at 01:24:48

So, I received got a Quad of KT66 from Decware a few weeks ago and have been enjoying breaking them in. Yesterday, after a brief morning listening session, I left the system up and running (idle) and did several hours of choirs outside and in the garage. I came back in around mid-afternoon and started listening to Tidel, after about 10 minutes I started to notice the some minor distortion in the right channel which progressively worsened over the next few minutes. I messed and fiddled with everything, restarting all my components down to the modem, the distortion persisted so I shut down the MKIV and let the thing cool down. I replaced the EL34's and fired the amp back up, everything was fine the rest of the evening. This morning I fired everything up and did little listening, EL 34's still in from the day before, everything ok, then the distortion started in again, hmm, grabbed an "ove'glove" from the kitchen and pushed around on the tubes just because and noticed my right channel OA3 tube flickering on/off, so I figured I found the problem. I shut down, pulled the OA3 out and grabbed a light to inspect the tube socket, everything looked good to my not really trained what to look for eyes and decided to switch the two around just for kicks, did that, fired the amp back up and no distortion for several hours, decided to go back to the KT 66 and see what would happen, switched them back in and ran them pretty good for about ½ an hour everything ok, let them sit and cook with no signal for a few hours while I finished yesterdays choirs and back to listening, so far even pushing them hard they are preforming great.
So my question is does that sound like I probably got a new tube going on me or is it something I haven't even ponder yet. I'll obviously keep this updated as I continue to listen, but I have to think that with the extent of the distortion that something is up and the OA3 thing was coincidence or ??. Any thoughts appreciated, sorry for the wordy explanation, but wanted to hopefully describe all the circumstances. Good listening to you all tonight!

Best,
Scott

Title: Re: New KT66 Failing?
Post by Archie on 12/04/18 at 01:32:47

If I read right, the distortion happened with both the KT66 and EL34 tubes but stopped after you swapped positions of the OA3s? Seems like maybe just a bad connection in the OA3 socket that cleaned up by the friction of pulling and inserting tubes? If you can get the distortion to switch channels by swapping output tube side then I'd be more inclined to blame one of those -- but less likely if it also happens with completely different output tubes installed.

Title: Re: New KT66 Failing?
Post by Jeff of Arabica on 12/04/18 at 01:57:17

Quote:

Seems like maybe just a bad connection in the OA3 socket that cleaned up by the friction of pulling and inserting tubes?

That would be my guess too. Or one of the OA3's has a loose/broken connection that stabilized after removing and reinserting. If that is the case, it will likely happen again. I would leave the suspect OA3 in the left channel socket and if the distortion re-emerges and the OA3 is the cause, it will shift the distortion to the left channel.

Title: Re: New KT66 Failing?
Post by ScottNC on 12/04/18 at 02:12:20

No, sorry for the confusion, got myself confused with it, it happened again after I thought it was the AO3, after switching positions and the loose connection problem gone. Replaced the KT66s got distortion then shut down, changed nothing and turned back on, and good so far... very strange or no, I'm not sure if it might be the start of something or what, guess time will tell, but I just don't quite get the progression of a tube going bad.
Thanks, I guess we'll see

Best,
Scott

Title: Re: New KT66 Failing?
Post by Jeff of Arabica on 12/04/18 at 02:17:31

Have you switched the two right channel KT66's with the left channel KT66's? I would do that asap. Then if it happens again, if the problem appears on the left channel, then you know it is a bad KT66 tube. If the problem occurs on the right side again, then could indicate and internal issue.

Title: Re: New KT66 Failing?
Post by ScottNC on 12/04/18 at 02:25:50

Thanks Jeff, that'll be my next move when it (and if) happens again, pretty sure it will.

Scott

Title: Re: New KT66 Failing?
Post by Archie on 12/04/18 at 15:53:07

You did say that you also had distortion with the EL34s? (before you moved the OA3s)

Title: Re: New KT66 Failing?
Post by ScottNC on 12/04/18 at 16:09:38

Hi Arch,
No distortion after switching the OA3's socket to socket with the EL34's, then put the KT66's back in and got after about 20 minutes distortion in the right channel, shutdown, changed nothing and so far for the rest of the evening and today everything good.
I'm hoping it just stays away, my one question is, and time will tell would it be that unusual for a tube that is going bad to be ok for some extended period before the problem shows up again? Seems weird, but I just don't have the experience to answer that one, any thoughts? Thanks again for everyones time on this, listening now and all is good [smiley=10.gif]
Best,
Scott

Title: Re: New KT66 Failing?
Post by Archie on 12/04/18 at 17:05:32

Quote:

... This morning I fired everything up and did little listening, EL 34's still in from the day before, everything ok, then the distortion started in again ...

This is why I thought you had distortion with both the KT66s and the EL34s. If it's just with the KT66s then Jeff has the next step. I've also chased tube issues that I couldn't reproduce. Glitches in the machine! I think when things get heat soaked you can have different effects. I've had radical issues with my CSP3 tube sockets that simply aren't there anymore -- but may come back! :-/

Title: Re: New KT66 Failing?
Post by ScottNC on 12/04/18 at 23:55:54

Arch, I got myself totally confused by all the switching! The good news so far is the amp has been playing great music all day long without so much as a hiccup.
I'm putting it down to some weird deal, more than likely UFO related, due to the location it was build and where the tubes are from [smiley=10.gif]. Thanks all for the input and replies.
My ZROCK2 is like a heartbeat away from hitting the bench!! TicToc ;D
Best,
Scott

Title: Re: New KT66 Failing?
Post by Archie on 12/05/18 at 15:55:15

Who knows, maybe some contaminant burning off inside a tube?

Title: Re: New KT66 Failing?
Post by ScottNC on 12/09/18 at 17:34:43

Found it! Finally worked through a methodical process of elimination and found the failing KT66, thanks to all the suggestions and experience offered. It took a lot of time, but I learned a whole lot from the exercise. I guess the next step is a call to Sarah, I'm figuring they will want all 4 back to evaluate, check and get a new one matched up.
Thanks again for all the help everyone.
Best,
Scott

Title: Re: New KT66 Failing?
Post by Archie on 12/10/18 at 00:38:39

Cool! It's always stressful when something odd happens. Glad it was just a tube.