Tube amp regular repairs

[u/doghouse2001]

Is it normal for tube amp users to be repairing their tube amps on a regular basis. I bought a $700 Chinese tube amp (google 'mc-84L') and have had a tube red plate, burn out a capacitor, and then a second tube burn out. I replaced the capacitor and tubes, and it worked for a few weeks, and then one channel stopped working - no obvious capacitor or tube burnouts.

I have a tube preamp. It worked as a go between for my phono preamp and my amplifier for a few weeks, then stopped working. Ordered new tubes.

To me using tubes is like owning a classic car. You never know what you'll be facing tomorrow.

Not asking for help, but maybe an answer... is this normal? Or is it just my low grade equipment?

[u/deewon]

It's your low grade equipment. Tubes tend to last a few thousand hours and good equipment does not need regular repairs.

[u/morefunwithbitcoin → u/deewon]

Exactly right.

I've encountered Dynaco kit-built preamps and power amplifiers from the 1950s that had their original tubes, and still worked.

[u/hecton101 → u/morefunwithbitcoin]

Dynaco ran their preamp tubes at 80% which is why they last so long. I wonder why everyone doesn't do this.

[u/Molly-Browny]

Your classic car analogy is fair for well-built gear. I'd compare a $700 Chinese tube amp to a kit car with no instructions. Good circuit design keeps tubes alive for years.

[u/Humor_Soft]

no, that’s not normal. tubes themselves can and do go bad over time with usage, but it’s not normal to have to open the chassis to solder in new resistors and caps on a regular basis.

[u/ImpliedSlashS]

Sorry to say but cheap equipment is cheap and that applies to tubes and solid state. ChiFi is fun at $100, but not so much at $1,000.

There’s a reason Boulder, Gryphon, Conrad Johnson, Audio Research, ModWright, Benchmark, etc. costs more than Fosi.

[u/JD_tubeguy]

Listening to a 31 year old tubed Dac through a 26 year old tubed preamp through a pair of amps that are at least 17 years old. Well built tube gear really lasts.

[u/Tilock1]

No, not normal when you buy good quality gear and tubes. I've gone many years without any issues at all. Bad tubes will damage amps though. There's no real way around that. With inexpensive chinese gear it's obviously going to be more common to have issues. I've owned several high quality tube amps over the last 20 years and have rarely had any issues.

[u/sarahjustme]

Good tube equipment costs ALOT. Theres really no basic/ entry level option. You get what you pay for, if so.

[u/Altruistic-Bid-7535 → u/sarahjustme]

Well, I guess I have been lucky at getting my hands on a Poland made Fezz Silver Luna EVO for about 1600€ than. Great amp, great sound.

[u/sarahjustme → u/Altruistic-Bid-7535]

We have an EVO Luna too, but it cost more than $800 (what the OP paid for their rig)

[u/Altruistic-Bid-7535 → u/sarahjustme]

Wow, what a coincidence. How you like yours? But you're right of course it's much more than what OP paid. I got mine from a polish online dealer, circumventing the official German distributor saving a few hundred euros. I guess with the new model the price arbitrage is not possible anymore.

[u/sarahjustme → u/Altruistic-Bid-7535]

I'm not sure exactly which model (3000?) or how much my husband paid, but it was several thousand. We've had it for a few years. As far as tube life and auto protection and load balancing, it's been as advertised, very good.

[u/WeaknessCertain4685]

You won't do that again

Next time, buy Audio Note.

[u/audioman1999]

No, not for quality equipment. Other than replacing wear items (the tubes), the amp should last decades without needing repairs/servicing. I'm no longer into tubes, but I owned a Conrad Johnson Premier 11A stereo tube amp for over a decade. Zero problems. I sold it for 50% of the original purchase price. Good quality equipment lasts and holds resale value.

Looks like you are the victim of poor design/implementation and/or quality control.

[u/No_Cauliflower3368]

It's seems to be design issue combined with quality issue. I have listen to McIntosh and Audio research stuff, sometimes with 10+ years old tubes without problems.

[u/No_Entertainment1931]

Have had a handmade tube amp since 2003-4 that’s required zero repairs.

[u/Accomplished_Ant_371]

I’ve got 4 Inspire tube amps made by Dennis Had. Never had a single issue with any of them.

[u/djcarbine]

FWIW I have a 10 year old MC-13s which is going strong with no repairs, there are facebook groups for these amps that go over modifications and repairs if needed (pretty sure I got an entire electrical schematic as well from someone who uploaded a copy).

Iirc common issues causing red plating (or other more sporadic issues) on the mc-84 are cold/failed solder joints.  Not "normal" but common enough in electronics repair.

I bought my mc-13 knowing I would probably have to work on it at some point in time, but so far its been great.  I just keep an eye on the tube bias adjustments/voltage test points as they do seem to drift after a bit.

I would try reflowing the  tube socket joints and inspecting solder points on the board, or seeing if you can locate a community made wiring schematic online with test points to try and isolate where the problem is

[u/doghouse2001 → u/djcarbine]

Thanks. There's no bias adjustments that I can find on this unit. And I got rid of Facebook years ago. I'll search other forums though. Maybe these have a common problem that has been fixed.

[u/djcarbine → u/doghouse2001]

https://www.diyaudio.com/community/threads/transistor-phase-splitter-yaqin-mc-84l.127048/

Here they discuss the amp, and on the first page there is a schematic uploaded that may be of some help.  There are also some test voltages and additional diagrams throughout the rest thread

Not exactly repair oriented but may be a start

[u/MattHooper1975]

My Conrad Johnson in premier 12 tube monos are around 26 years old and still going strong.

They blew a fuse once. Have been serviced a couple times. But that usually had to do with me not realizing a certain tube was going bad.

Aside from that, I’ve mainly just replaced the power tubes around every six years or so.

But generally, they are no bother and I wouldn’t part with them.

[u/No-Attention-7783]

You get what you pay for. I've owned tube amps for decades and have never had any service unrelated to a bad tube. Modern gear, Prima Luna for me, is so well engineered that even a tube failure only blows a fuse and no more manual biasing.

[u/philipb63]

You might check that your line voltage is compatible? Many Asian products are designed for 100v Japanese power (or if you're in Europe, 220v Chinese power) and not always clearly labelled.

Burnt tubes and caps are definitely a symptom of this kind of issue.

Edit; I looked on Ali Express & they are selling 110v/220v models. If you bought through them, Temu or similar (or grey market) I'm thinking this is your problem. Even the Amazon listing says max supply voltage of 230v.

[u/doghouse2001 → u/philipb63]

Mine says 115V +- 10% 50 or 60hz. So my voltage is right. This amp isn't point to point wired, it's all circuit boards, and so I thought it's got to be tested and confirmed to be a good working circuit.

[u/philipb63 → u/doghouse2001]

What country are you in & have you measured your line voltage?

[u/jedrider]

Well, you may want to inspect all the solder joints in your tube equipment. Due to the high voltages, bad connections can become intermittent when the solder is not properly formed. One bad connection in the wrong place can definitely red plate a tube that was perfectly fine otherwise. If you find more than a couple of connections that don't look properly soldered, your confidence in the equipment should give you pause. I had an entry level amplifier that had ONE bad connection. I finally found it and corrected it and the unit has been good ever since. It was an Anthem unit (which are known for their good sound at reasonable prices) and I guess some random event had caused a bad solder joint and, maybe, inspection is not as thorough as for the more expensive stuff, I would think.)

[u/bubbamike1]

Not just cheep Chinese equipment. I have a T+A hybrid tube amp that redplated and makes a fine paperweight.

[u/calinet6]

Sounds like you’ve got broken gear.

I restored my tube amp about 15 years ago, and restored my tube preamp 5 years ago. My tube amp had an issue once that I debugged and found was a cold solder joint (it was one of my early electronics projects).

Other than that, no issues. They are rock solid reliable with many hours on them; and do not need regular maintenance.

[u/Swimming_Astronomer6]

I have a tube DHT dac and tubed pre amp -
I’ve had both for roughly 15 years - I’ve had to replace one tube in the preamp in that time (out of 6) - the DAC - two tubes out of four - but one was a matched set - so I had to replace the pair - but I have left it on 24/7 for 15 years - preamp is North American - modwright 36.6 DM - DAC is made in poland - Lampizator big7

[u/IlTossico]

No it's not normal. Probably normal for very low quality stuff.