2. amps-preamps
  3. 161800-92835

100 W Tube Amplifier Malfunctioned

I will not name the brand of the malfunctioned amp in question, except to say that it is a US brand and it is not a boutique shop. I bought direct from factory as there were no dealerships in my region of the world, Taiwan. As I traded in my old amps, I was given a discount and paid $5,000 for the pair. 

My system consists of a Verdier Turntable, A MFA Luminescence preamp, a Wadia 16 CDP and Eminent Technology LFT 8b speakers. The amps were brand new and worked well for 6 months. Then one of the amps malfunctioned. I sent it to a local technician, and determined that the transformer was shot. 

The malfunctioned amp was sent back  at my expense. After inspection,  I was told that the amp failed because it was operating over voltage. Our power grid delivers 110 v electricity.  And in order to be certain, the other amp which was perfectly fine was requested to be sent back for inspection. 

The solution for repair was to increase the VAC of the amp to 125 V, obviously for both amps, and the tubes will be inspected and biased accordingly. The cost for repair will be $ 850 for each amp. My questions is: Should I pay for the repairs? I was told the reason for the failure was due to the fluctuation of our local power grid. Therefore, the user is at fault. However, if it is  power grid is the problem, then why did only one amp fail? Would it not be a reasonable assumption that there are quality control issues at fault? 

Given that there are brand new amps ( six months old ), isn't paying $ 1650 for repairs unreasonable? Any insight would be appreciated. 
ledoux1238

Showing 2 responses by millercarbon

millercarbon's avatar
millercarbon
12,531 posts
 
Transformers don't go like that unless they're defective. Not your fault. Not your responsibility. Theirs.
millercarbon's avatar
millercarbon
12,531 posts
 
However, if it is power grid is the problem, then why did only one amp fail?

Without saying anything one way or the other about what truly caused this problem, this question at least is easy to answer. IF - IF! - it is anything to do with voltage fluctuations then there's really only two ways it can go. One, the surge is so powerful it blows out everything in its path, no amp can survive, and they both go. Or Two, its marginally out of spec and so it comes down to one component part somewhere in the amp hitting its limit before the same component part in the other amp. This can easily happen. In order for some marginal fluctuation (which it sounds like it is) to cause both amps to fail simultaneously would call for an almost superhuman matching of identical tolerances across all components in both amps. I know we all like to think that's the case, but its just not. 

That said, the questions I would be asking are very different. First and foremost I would want to know exactly what failed? Was it rectifier diodes? A resistor somewhere? Did a failure in one part start a cascade of failures down the line? What happened? Exactly. Give me the forensic breakdown. If its a lot of stuff, then explain to me why I should be buying another one of these designed to fail so expensively from so minor an AC fluctuation?  

Most of us never look inside our components, which is a shame. All it takes is a cursory glance to see lots of parts like caps marked with their values. Resistors are a little harder because you have to decode the color bars. But once you do everything is right there out in the open. If a tech tells you a cap failed because your voltage went from 110 to 115 then you open up your other amp and say which cap? This one right here that says 600V right on it??? Like that. Other parts like rectifier diodes have parts numbers printed right on them, that can be looked up on the internet to find their rated values. This can be done with virtually every single thing you can find in there. 

What you will find if you do this, a huge amount of the parts in there are very conservatively rated just like the 600V cap example. Its just nuts to say voltage going up a measly 10% (which is what we're talking about) caused thousands of dollars worth of damage. Not if we're talking a competently designed amp. Which admittedly is precisely the question. Which you only find out by digging into the details of exactly what part(s) inside the amp it was that failed, and what specifically the parts are that will change this- and will they, really? 





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