2. amps-preamps
  3. 1204287063

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
mlsstl
1,424 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.
tiger
313 posts
 
Quickly ditch the unit back to the dealer for a fully 100% refund and stay away from the brand. Make it a dealer problem. Move on, quickly.
rlwainwright
1,904 posts
 
Replace the burned tubes with the stock units. See if the problem goes away. If it does, you're finished. Also, why is everyone so reluctant to provide the name of mfgrs. here? It isn't as though you said anything libelous.

Give us the mfgrs. name, please.

-RW-
undertow
1,033 posts
 
#1 - Fact is you had no choice but to replace the tubes since the first unit took them out in the first place..

#2- no it should have nothing to do with a warranty putting different but correct tubes in the unit.

#3- at the VERY least the dealer should provide you with a brand new set of Stock tubes free of charge, as the manufacturer does have at least a 90 day warranty or so on tubes period I would assume, you have done nothing wrong with trying to correct a problem from the get go and make it better considering the only reason you put NOS tubes in the unit was the originals turned to toast on a brand new unit which you would not even considered doing it this early I am sure..

It seems if the dealer is giving you an issue on this then it is not explained to them correctly that THEIR Stock unit was toasting itself in the first place, and you just tried to rectify it, however you need to realize your loss in the NOS tubes is not their responsibility.. But the Stock Tubes absolutley are, and they can take the unit back, re-tube with stock, and refund you and take their chances on selling it again on their own.. You should have a 30 day return policy with them anyway.
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