[Niteshade]

I started this thread because of where another was going and I wanted to address this concern. Has anybody had a significant number of problems?

As long as a tube amp has good ventilation and is properly biased, there shouldn't be any major issues with well designed equipment. Sometimes tubes have manufacturer's defects, but that shouldn't be a giant issue.

[JoshK]

I haven't, but I haven't owned tube amps for very many years.  I have to imagine that issues with reliability are inability of the user to properly set bias or tube reliability.  Tube failure can take out many other components, especially since many tube amps don't have much in the way of protection built in.  Transistor amps, particularly bipolar amps, pretty much require speaker and circuitry protection because of the way they fail. 

I have to imagine this has more to do with the abundance of inexpensive (cheap) tube amps from asia. Not picking on asia, but if cost is the driving factor then lots of care and quality is bound to be absent.

[Freo-1]

I haven't, but I haven't owned tube amps for very many years.  I have to imagine that issues with reliability are inability of the user to properly set bias or tube reliability.  Tube failure can take out many other components, especially since many tube amps don't have much in the way of protection built in.  Transistor amps, particularly bipolar amps, pretty much require speaker and circuitry protection because of the way they fail. 

I have to imagine this has more to do with the abundance of inexpensive (cheap) tube amps from asia. Not picking on asia, but if cost is the driving factor then lots of care and quality is bound to be absent.

Josh brings up some good points. I've owned both tube and solid state for many moons now, and find that both types can be reliable or problematic.

Regarding tube amps, power tubes are the only area that I've had issues with.  Current production power tubes just do not seem to be as reliable, sound as good,  or last as long. The reliability issue can be minimized by proper screening and testing. I don't trust current production 6550 to last much past 1500 hours or so.  One of the most highly touted current types has given me trouble, but the SED 6550C seems well made.  Personally, I stick with NOS power tubes, and have had excellent luck with them.

I've also had both good and bad solid state amplifiers as well.  A lot of the higher end solid state amps have had suspect reliability.

Truly, it "horses for courses" with this issue. I personally prefer tubes for music, but very much enjoy movies and DVD concert videos thorough a flagship DA9000ES unit. 

[DaveC113]

I have a tube amp and preamp, the pre for about a year, the amp for a few months.... so far I have had 2 rectifier tube failures. A used Sovtec that came with the pre failed, popping noises started coming from the speakers and I unplugged it before anything happened. Later, a JJ rectifier started shorting the ps caps to ground through one of the filter resistors. It destroyed a couple resistors and fuses before I found the problem. This happened about 30 seconds after I turned the preamp off.

I am using new TS 6550 tubes in the amp, they have been fine for over 500 hours now. The side getters are showing a touch of wear, but they still sound great.

The pre uses 4 6922s and 2 12at7s, never had an issue with any of them, used or new.

[Niteshade]

What are some of the most reliable tube manufacturers and types in your opinion?

[Ericus Rex]

Sovteks are regarded as very reliable, but I had a new 12AX7 fail after only 100 or so hours.  I've also had a new-production Mullard EL34 blow on me after a couple hundred hours.  I've never had a problem with the other tubes in my system - JJ E34L, EH 6922, Sovtek 6922 and a few NOS oddballs.  But even with the failures, I'll continue to use new-production (vs. NOS) due to cost.

As for equipment itself,  I've had both tube/SS types fail on me.  I tend to buy older, more 'classic' gear which could be part of the problem - older caps, and such.  But nothing so far *KNOCK ON WOOD* has been beyond replacing a small cap, resister or bridge rectifier.  Aside from a couple of tubes, the past four years have been repair-shop free.

[Niteshade]

Some of my favorite tubes:

Ei 12AX7's and 12AU7's
Chinese 6SN7's & 5U4's
JJ/Tesla 6L6's & KT-88's
Sovtek 5881's & 6L6WXT+'s & EL84's
Chinese 845's & 813's

The JJ/Tesla 5AR4 isn't such a good tube, Russian (no name) 6SN7's are noisy. Chinese 6L6's are great for low power applications and that's it.

[JimJ]

I've been impressed lately with the Svetlana power tubes derived from RF designs...the SV811-10's I've been running the past few years haven't had any problems.

[zacster]

JJ 12AU7 is reliable
Sylvania 5U4 is very reliable (50+ years old in use in a TV and now my amp)
Amperex orange globe and bugle boy 6DJ8 and 6GM8 are reliable.
Sovtek is NOT reliable.  I use the Sovtek 6B4G and I burn through them, but my amp also pushes them very hard.  Other Sovteks have also given me problems.

As far as tube amp reliability is concerned, I won't leave mine on unattended.  I let the smoke out one time and it was close to starting a fire.  And early solid state had the same problem.  Current stuff isn't an issue.

[Niteshade]

I have been under the impression that directly heated triodes would be more reliable. They were made for intense service schedules and have allot of space between components. I also like the idea of tensioners on filaments. There is a Russian 5U4 that has filament tension springs, with a "W" filament shape. I have some of those and really like them.

I've been impressed lately with the Svetlana power tubes derived from RF designs...the SV811-10's I've been running the past few years haven't had any problems.

[JohnR]

I've had issues with cold joints in P2P amps, and bad sockets.

I'm just wondering, however, if you might consider not starting so many threads (i.e. use the ones you already started instead of new ones all the time), and also not starting them outside of Industry Talk. I don't believe you are doing anything against the rules, and I would really hate to in any way discourage your participation as it's been great to have these discussions, but there does seem to be a certain level of annoyance amongst some members with your posting practices, and it would not be hard to correct. Thanks

[Niteshade]

ATT: Small signal tubes & large signal tubes that burn out quickly.

One of the favorite ways to control tube output is to reduce the resistance of the anode resistor. Unfortunately, that puts stress on the tube if the cathode resistor is small. A better way to do things is to make sure tubes such as the 12AX7, 6SN7, etc... have lower voltages applied to them. I would say around 240 volts, then design the circuit around that.

Large power tubes that die quickly: Putting manufacturer's defects aside, there are many ways to kill power tubes that I am aware of:

1. Run the tubes too hot either by incorrect biasing and/or poor ventilation
2. Placing the power tubes too close together (again, heat)
3. A phase splitter that's not working properly, allowing one tube to do all the work
4. High voltage too high. There's no need to go above, say 440v for a 6L6 or even a KT88
5. Running push-pull amps too close to Class A. (heat)

Something I recently did: Place a 10" cheap box fan near my tube amp. I never liked convection cooling for electronics, either SS or tube. It runs on low speed and allows the amp to achieve a perfect operating temperature. The noise is unnoticeable when a movie or music is playing. It's not loud anyways.

[Niteshade]

Hello John,

I have been thinking about message clutter and ways to prevent it. I do not have a circle on here and don't know what to do to obtain one. Industry ads are for business related posts and many of my topics lie outside that, as do the ones that provide people information on other circles. It's difficult to discuss, say this subject on top of a thread about something completely different like phase splitter designs. It wouldn't make any sense. I have been asked to keep posts in relevant forums and I respectfully say that your advice is confusing- yet the issue is acknowledged. Please be aware that it is difficult to operate under contradictory advice.

Thank you for your input and I'm glad you enjoy my posts. I like being able participate and to help others.

On to your question:

I despise cold solder joints. They are embarrassing! I had a new Ameritron AL-80B HF amplifier that worked great for two years until one day the filament kept flickering on & off. The manufacturer forgot to solder a  wire on the tube socket. Easy fix. There are ways to preventing cold solder joints.

1. Make sure the iron is on the proper temperature setting.
2. Be PATIENT and let the solder flow
3. Use a flashlight if necessary to make sure solder flowed around ALL the wires on a turret or in a lug.

Bad sockets: Surface mount sockets and P-P sockets have the same problems. A jeweler's screwdriver (small one) can often be used to tighten spread contacts with octal sockets. Other than that, I have never had a socket go bad on me. 

I've had issues with cold joints in P2P amps, and bad sockets.

I'm just wondering, however, if you might consider not starting so many threads (i.e. use the ones you already started instead of new ones all the time), and also not starting them outside of Industry Talk. I don't believe you are doing anything against the rules, and I would really hate to in any way discourage your participation as it's been great to have these discussions, but there does seem to be a certain level of annoyance amongst some members with your posting practices, and it would not be hard to correct. Thanks

[JohnR]

I didn't have a question, I was answering yours about reliability problems with tube amps.

[Niteshade]

Oh- Sorry! You're quite right! Well- that's how I try to prevent/fix those problems.

I didn't have a question, I was answering yours about reliability problems with tube amps.

[JohnR]

It's good advice, but finding out which joint is the bad one is the hard part... In my case (a commercial amp, not one I built) everything was fine until the amps warmed up, and then it would just.... rustle... every now and then. Very annoying, took me months to find it.

Don't get me wrong, I love tube amps, although I don't have any operating here at present (long story). I do wonder though, now that this topic has been brought up, if point-to-point wired amps are more susceptible to joint failure than e.g. PCB amps, because of the stress put on the joint when tubes are inserted and removed. That is, if any joint on the socket is not absolutely 100%, then it will fail sooner because of that additional stress.

[Niteshade]

"...point-to-point wired amps are more susceptible to joint failure than e.g. PCB amps, because of the stress put on the joint when tubes are inserted and removed. That is, if any joint on the socket is not absolutely 100%, then it will fail sooner because of that additional stress..."

I'd believe it would be about the same. I never thought PCB's were tolerant of cold joints because the sockets can move in the board's holes which could lead to torn or lifted traces.

I had a prototype about three years ago that made rustling sounds as it warmed up. It was difficult to pinpoint because it was not due to a poor physical connection. I used soldering flux in it for a few locations and what had happened was the flux made a bridge between ground and the contact where it was used. It wasn't even visible, but you could feel where the flux flowed between the terminal strip lugs. Some contact spray fixed it.

[JohnR]

Sure, that's a good point, I guess in my wondering out loud there I was assuming that a board would provide some physical support for the socket pins, but I can also attest to having to deal with some seriously lifted tracks on PCBs (mostly not by me, although I admit I have had my moments...)

So in the end I guess it comes down to skill and QA.

[Niteshade]

During my old job at GnNettest, I worked with printed circuits 8-10hrs a day. We had good equipment and almost everything was surface mount, which works better with PCB's since it doesn't take as much heat to add/remove components. The wires that connected boards to displays and batteries could be an issue, but  all contacts have very little stress on them.

Josh has a great thread relating to a DIY KT88 single ended amp that has some of the best PCB material I've seen. They made it so the board doesn't flex much and the designs are modular- a giant plus.

[Bill Baker]

As long as a tube amp has good ventilation and is properly biased, there shouldn't be any major issues with well designed equipment.

 One of the biggest issues with tube amp servicing has been consumers installing tube amps in a confined space without proper ventilation. The rising temperature within the chassis can cause premature failure of passive components.