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Second failure of new amplifier

Two weeks ago I burned my new amplifier equipped with eight 6L6 tubes. I had been using the amp for one week before that and everything was OK. The failure occurred when I was switching the amp to the standby position and then to the "off" position (two small tubes and two central power tubes flared, so I switched it off and disconnected from the mains immediately). Switched on - no sound. I found out then that the failure was caused by one damaged 6L6 tube and one burnt fuse.

I replaced the fuse and one tube and everything was OK, until I decided to listen to the music today. I listened to it for 15 minutes, then the same problem occurred - when I was switching it to the standby position and then to the "off" position, there was a clapping sound, one 12AU7 tube ignited (flared strongly) and the tubes do not glow after switching on. I will explore this problem further when I come back from work.

When I was purchasing this amplifier (I would prefer not to disclose the manufacturer), my local dealer claimed that the amp had a "stabilized power supply design" or something like that. One of my audiophile friends dissuaded me from bying this amp, saying that 4 output tubes per channel may cause a problem. The dealer said "don't listen to him - he does not know what a "stabilized design" means."

I think I know now what is "stabilized design" - it's burning fuses and tubes every second day. My dealer is reluctant to take it back even for resale (I suggested that he took it for repair and sold it and only after that give me money), but he claims that the guarantee is void because I replaced the stock tubes (12AU7 and 6922) with my own (vintage)tubes and that I should have waited for a couple of months (while it was burning-in) and should have used it with stock tubes without replacing them for other tubes. He added that according to the European ISO standards, changing the tubes would void the warranty.

My questions are:

1. Does tube-rolling in a new amplifier always void the warranty?
2. Is it true that the auto-bias function (especially when the amp is powered with so many (8!) output tubes is unreliable as compared to manual bias adjustment (like my other amp - Cary SLI-80)?
3. Is it normal when a brand new amplifier behaves like this?

I will appreciate all comments, opinions and suggestions.
transl
thorman
1,262 posts
 
I wouldn't do a thing until I cleared it with the Dealer you bought it from..As far as I am concerned they ( dealer ) should take responsibility from here..There is something going on internally ( my guess ) that is causing this to happen..You shouldn't have to mess with tubes for at least a year or two..I also wouldn't start rolling tubes until you realy give your ears and your new piece a good chance..
No it is not normal..and rely on your Dealer for help!!!!You can find out how he can Stabilizes the situation!!!
rcprince
3,070 posts
 
Does the amplifier exhibit the same behavior with the stock tubes? I would suggest putting them back in and seeing if the problem occurs again--if so, then the problem may not be attributable to the NOS tubes. I would not think tube rolling with tubes of the same type should necessarily void a warranty, but you'd have to read the warranty to be sure, and this sounds like a European law question with which I'm not familiar anyway. In any event, I agree with Thorman, your dealer should be fixing this problem for you; just make sure that it in fact is a problem with the amp and not with your tubes. This does not sound like normal behavior for an amp. As far as autobias circuits, Jadis has had them for years with their amps; I never had a problem with my JA80s relating to that circuit.
rodman99999
6,130 posts
 
As long as you rolled the tubes with tubes of the exact same family(IE: 6DJ8/6922/6H23/7308/E88cc/E188cc/CCa) it should not void the warranty. Burn-in time has absolutely nothing to do with an amps affinity for blowing tubes. Sometimes the translation from another language can make a warranty sound like tube changing will void it. The Lector CD player warranty SOUNDS that way(via translation), but the designer is a veteran tube roller himself, and rolling does not void their warranty. Contact the manufacturer, and request that info directly. I don't believe the driver or phase splitter tubes would be taken out by a problem in the auto-bias circuit. It sounds more like a power supply/transformer issue. Again- Contact the manufacturer. Solid state servo bias adjusters that tweek each output tube's bias on the fly, on a continuous real-time basis("Auto-Bias Circuitry") are great in that they 1)free you from having to buy matched sets of output tubes 2)eliminate the possibility of you mal-adjusting the bias 3)keep the tubes running exactly where they should.
mlsstl
1,436 posts
 
You weren't clear if the tubes you installed were the the same type as the factory installed. If you replaced the 12AU7 and 6922 with the same types it should NOT void the warranty in my opinion. In the close to 40 years I've been an audio electronics hobbyist (building, repairing and modding - I've got the scopes, distortion analyzers, meters, freq generators, etc.) I've never heard anyone else state that changing a brand of tube voids a warranty. I'd strongly question that. I'd want to see a copy of the "European ISO" regulation with my own eyes.

Now if you were experimenting with different types of tubes there could be an issue - the pin-out or operating characteristics could be different and cause a problem.

However, step 1 is to figure out what is currently wrong with the amp. If putting the original tubes back fixes the problem, you may have had nothing more than a defective tube. If something more is wrong, it still needs to be found. No manufacturer has 100% quality control and it could be that while a part passed the initial QC tests it might have been marginal and was doomed to fail in a short period of time no matter what you did or didn't.
transl OP
156 posts
 
This is a question of dishonest dealer, for sure. If I were in his place, I would make my best to maintain good reputation.
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