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

Showing 9 responses by transl

This is a question of dishonest dealer, for sure. If I were in his place, I would make my best to maintain good reputation.
OK. To resolve the second failure, I replaced the fuse and installed the stock pre-amp tubes. The amp sounds terrific, by the way (which makes me think that some modern amplifiers are optimized for modern tubes - if you replace them with NOS tubes, you sometimes hear "mushy" sound and a loss of focus)... I will see how it behaves with the stock pre-amp tubes.
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).
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.
I want to thank all guys for compassion and understanding. I haven't decided yet what to do - the dealer keeps (and will obviously continue to keep) silent, while the amp is working OK with the stock tubes, except that I installed the Mullard CV4110 tubes in the 6922 position (tomorrow I expect NOS TungSol 5881 tubes to arrive and I am not sure whether I will install them or not under the circumstances). I will be watching for the amp's behavior.
Amp failure update:

Yesterday I received an octet of brand new NOS/NIB TungSol 5881 tubes (60s vintage). Trembling with fear, I inserted them in proper positions and listened for a couple of hours. Even in half an hour, the sound was fantastic. I switched the amp off without a problem.

Today in the morning I switched the amp again and very soon heard some noise (cracking sound) from the left speaker. Switched the amp off, let the tubes cool down and swapped the output tubes from left to right and vise versa (exchanged the channels). The problem did not appear again. Went to work. Will resume the listening in the evening. What could have caused the cracking sound? Gas burning inside the tube(s)?
The manufacturer's name transpires from the previous posts, so this thread is not a speculation.

Here is the response I received from the manufacturer:

'I understand your disappointment for a malfunction of a new equipment. But let me tell you that I don't agree with your request to return the equipment to the dealer, loosing money. I believe you buyed the amplifier as you liked it, and you have the right to own a perfectly working equipment.
Our goal is the customer satisfaction and if you were in Italy I should have requested you to send the unit to our factory for a careful control: this is the first time an ADM35 or ADM32 has such a problem and we are interested to investigate the causes.
Unfortunately the distance between Russia and Italy does not allow it.
Anyway, please let me be informed about the operation of your amplifier: I hope the malfunction was a temporary problem, and you can enjoy the ADM 35 and the CTR-2.'

Rather vague and inconstructive...The amp is now working with vintage TungSol tubes, by the way.