2. amps-preamps
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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
transl OP
156 posts
 
Gs5556:
'Curious... why use the standby switch to power down?' - how can I avoid the standby switch? Shall I make two quick clicks - standby and then immediately to the "off" position?

By the way, the amp is working now. I replaced the fuse and installed the stock EH 6922 and 12AU7 preamplifier tubes. Sounds very nice! I will watch how it behaves with stock tubes. Afraid to roll tubes forewer (but not with the second amp - Cary SLI-80).
timrhu
2,779 posts
 
I gather you don't have much technical experience with tubes. You can get a tube data manual and find that any given tube
That made me chuckle as I began my life as an electronic technician back in the days of tubes. Used to have a tube tester in my garage. I fully understand the principle of suitable substitution.
That being said, I'll admit I don't know much about warranties for tube electronics. It still would surprise me if a manufacturer is obligated to replace a defective unit when the defect was caused by a faulty tube (not supplied by the manufacturer) being placed in the equipment by the new owner. Just an assumption as I haven't read the warranty agreement, I could be wrong.
If the product had a defective tube socket that wasn't apparent until the original tube was removed that's a different issue and Transl was fortunate to discover it. This needs to be discussed with the dealer.
mlsstl
1,436 posts
 
Timrhu, what would you say if Ford or GM voided your car warranty because you put in Bosch spark plugs instead of the Champions (or whatever) that it originally came with? Or limited your brands of gasoline to Exxon/Mobil only. ("I'm sorry, your warranty claim is denied since you used BP/Amoco gas.")

Another problem with that logic is the brand of tube used is often meaningless since many tube manufacturers are no longer in business even though the brand may still exist. Those tubes are being made elsewhere.

I have to say that in 40 years of involvement with the technical end of audio this is the first time I've ever heard someone trained in audio electronics claim a warranty was likely to be voided based on the brand of vacuum tube used. Interesting.
newbee
4,767 posts
 
Mlsstl and Timrhu, FWIW, a warranty covers exactly what it sez it covers (so long as it conforms to any State laws regarding warranties), not what you would like to speculate it should or should not cover. I don't see that Transl has ever told us what the warranty actually said.

While I'm a bit confused by the multiple comments regarding tubes initially rolled in, it looks to me as if the only tubes were the small tubes, not the power tubes, and I agree with those who have said that substituting brand A 6922 for brand B 6922 (for example) should not affect the operation of the amp and the failures experienced by Transl. Had Transl identified the actual amp perhaps someone here with hands on experience could have helped him. FWIW, something tells me that the problem lies in the standby curcuit's operation.
transl OP
156 posts
 
Neswbee:

- I was not given a warranty and I don't know what it says. The dealer, or, rather, the distributor, prefers not to give a warranty saying "I myself am a warranty". Perhaps he wants to conceal the original price by all means and to prevent a buyer to contact the manufacturer directly. He succeeded in it - the company's president stopped to answer my queries.
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