The short version can be found here.
A tough start…
I ordered a new Muzishare X7 Hifi Amplifier on Amazon.com from “TubeAmplifierStore” on September 3, 2022 for $1499.40 and received the unit about a week later.
My X7 started it’s life with a peculiar, but serious bug! Within the first few hours of running the amp, the left channel faded away and the KT-88 output tube in socket V3 was red-plating! Of course, I quickly turned the amp off and sat dumbfounded as to why this happened. Let me explain.
This Muzishare X7 is not my first hifi tube amplifier and I’m well aware of setting (and even tuning) grid bias for output tubes. And I was sure I set all 4 output tubes at the correct 40mA bias recommended by the amp manufacturer. It’s a new amp with new tubes as well. Now, I was expecting *some* fluctuation in grid bias as the components of the amp and the tubes get “settled”, but red-plating one of the output tubes was not expected by any means!
For the next few months, I struggled with the amp and it’s bias settings. Setting the bias on all the output tubes and keeping the bias at or near 40mA became an “every 10-minute” event. While doing so, the amp would red-plate an output tube once or twice a week.
Troubleshooting this was a nightmare! My X7 would red-plate any output tube in any socket?!?! I couldn’t track it down. At first, I thought I had a bad tube. But then I would switch tubes into different sockets, as one would likely do in trying to troubleshoot this, and a few days later it would red-plate the same socket, but different tube! Then I thought it might just be the V3 socket but a few days later, the amp would red-plate the tube in socket V1!?!? All the while, setting bias on all of the sockets V1-V4 was, at best, soft.
By this time, I thought I had a real problem with the amp but before I attempted the “warranty” route, I thought I would try a brand new set of output tubes, just to completely rule out possible bad stock KT-88 output tubes. It took a week to get them in, but I ordered a new quad set of matched PSVane Classic Series KT-88s at about $450.00 shipped! I installed them in the X7, set bias at the recommended 28mA for these tubes, and the X7 red-plated one of those tubes within 6 hours!
At this point, I knew I had to send the unit in for repair. On February 27th. 2023, I contacted “TubeAmplifierStore” through Amazon.com, explained the bias issue, and on March 3rd. 2023, I sent my X7 amp in to a repair shop in Wisconsin for warranty service.
I have all of the documentation, the back-and-forth dialog between “TubeAmplifierStore” and I getting the shipping approved for the initial return for service. I also have all of the back-and-forth email between the repair shop in Wisconsin and I trying to troubleshoot this issue on my X7. It’s kinda boring and a bit technical, and it took several weeks, but the repair shop ended up replacing both “bias boards” in the amp and sent my X7 back to me.
Now, initially I could tell that the repair shop had done the work. The bias seemed much more stable than before and setting the bias at 40mA was much easier and more targeted. So, I felt good that perhaps my strange bias “run-away” / red-plate issue was fixed. But, no.
On April 18th. 2023, I contacted “TubeAmplifierStore” with the bad news:
Well ****, it happened again…
In my previous attempts to isolate the bias issues on the amp, I purchased a new set of tubes for the amp, a new, matched quad set of PSVane Classic Series KT-88s. When I got the amp back from you, I ran the amp on this new set of tubes for a while and noticed one of the new tubes was a bit “squirrly” and would not stably bias. I contacted the tube retailer and received a replacement today. So, I rigged the amp with these new tubes.
So, I have a new set of output tubes, 3 of which have maybe 20 hours on them, 1 of which is brand new. I put the new tube in V1, the rest in V2-4 and fired it up at about 3:30p today. Burn-in time…
Biasing V2-4 was easy and about as stable as I would expect for new(ish) tubes. With a 40mA target, after about an hour, I got them biased fairly stable. V1, as expected, needed a few hours to get somewhat stable at 40mA, but I got it there. Needless to say, I keep my eye on the amp and the bias, checking about every 10 minutes and leaving the meter switch in some Vx position so I can monitor things. Come about 7pm, I got all 4 output tubes at or close to 40mA and running stable.
And then, right about 9pm, the right channel (V3-4) went dead, V3 bias on the meter was at full deflection, and V3 had a red plate! This thing was stable for hours before and if there was any concern, it would have been on V1, the new tube. All other output tubes were fine and showing close to 40mA. I shut the amp off and waited about 1 minute.
I then simply turned the amp back on, nothing else changed, and it’s not red-plating. The current timestamp right now is: 9:26pm and it’s been running for about 20 minutes now, no touch from me. The current bias status is:
V1 – 30mA
V2 – 40mA
V3 – 18mA
V4 – 40mA
These were all set at 40mA before the V3 red-plate episode, amp turned off for a minute, turned back on, and now it seems V1 & V3 are quite a bit off the target while V2 & V4 are right where they should be.
At this point, I had to take a step back and look at the bigger picture. I purchased a new amp from “TubeAmplifierStore” and that amp came with a serious defect. I’ve spent many hours of my personal time trying to troubleshoot this defect rather than enjoying the amp I purchased. I’ve invested more of my money in purchasing a new set of output tubes, way before anyone ever should have to on a new amp, trying to troubleshoot this defect. I’ve also gone without the new amp I purchased for weeks while in for “authorized warranty service”. And it’s still defective! Obviously, something is really wrong with the X7 I purchased, and I think it’s time, and fair to just replace the amp with a new unit.
This is where things go wrong…
After a bit of back-and-forth messaging to “TubeAmplifierStore” on Amazon.com requesting a replacement amplifier instead of trying to repair this one again, the exchange was approved on April 28th. 2023, however I had to pay for shipping my original X7 back to Wisconsin to complete the exchange!?! OK. Not much other choice but to play along…
Now, I asked for a new replacement, and during this time I made several attempts via email to clarify whether the replacement would be a new or refurbished amp. From the responses I got, I was led to believe I would be getting a new amp.
“I am sure we can get you a different amp. And yes I agree you shouldn’t be a part of my “find out what’s going on experiment” …I will talk to them tonight if you want about getting you a fresh one.”
“THey did agree to a swap, so I can get fresh X7 checked out over the weekend.”
“They replied last night, and they will have you ship back back your X7 and send you a fresh one from their stock.”
“Once I receive it I will let them know and they will ship a new one.”
So, I shipped my defective X7 amp UPS Ground with insurance to be sure, for $144.00, and they received the amp on Tuesday, May 2nd. 2023.
On May 5th. 2023, I received an email from the service shop advising me that my new amp was shipped via UPS Ground.
On May 9th. 2023, I received this used and abused replacement:
Are you tying to insult me?
Now look “TubeAmplifierStore”, I gave you my hard-earned dollars, and then some, I played your warranty game, by the rules, and you send me this? It’s insulting! Did anyone check this thing before you sent it to me? I’m a full-paying customer too. Is anyone paying attention?
I immediately contacted the service center from where it came, emailed these very pictures to them, and asked, “What now?” It was only then that they confirmed to me that I would not be getting a new replacement, but a “refurbished / used” replacement instead.
They sent me several pictures of another refurb/used amp that looks to be in much better shape than this one, and promised to exchange it, again for this abused amp. It’s May 16th. 2023 and I’m still waiting for someone from “TubeAmplifierStore” to advise me of the next step…
On May 16th. 2023, I decided I would try to “nudge” the process along by sending a message directly to “TubeAmplifierStore” about my current displeasure with the abused amp replacement they sent me. Several hours later I received a response reminding me that I am beyond the “Amazon Exchange Period” but they are making an exception for me and included a return shipping label. “Bittersweet” comes to mind. Still, fair enough.
I received the 2nd. refurbished amp on Wednesday, May 24th. and while this amp is in better shape than the last, it is not the same amp I purchased. This refurb amp does not have XLR inputs, the inputs I use, so I can only assume it’s an older model that didn’t include XLR inputs on the back. It does work. It sounds quite good as well.
Guys, I’m done. I do have an amplifier that works and sounds good, but it is not the amplifier I purchased, it doesn’t have the same features as the amp I purchased, and it certainly is not in equal condition as the amp I purchased. All told, I spent $1650.00, and a huge amount of my time and effort for an old, outdated, used X7 amp!
One final note:
I’ve had the current replacement amp for about a week or so now. I’ve been carefully watching how this amp runs. I am absolutely certain that there was something really wrong with my initial new X7 amp! A “manufacturer’s defect” for sure since it has always had a very “soft” bias. This used X7 I have now has a very stable bias. It’s a noticeable enough difference that it offers validity to my initial complaint. Why should I pay more and settle for less than everyone else who rightly purchased a new X7 with XLR inputs from “TubeAmplifierStore”? I’m not sure what else I can do.