After a busy Christmas season, including a brief trip out of state between Christmas and new year, I have finally managed to get the Lacewood amplifier back up and running. As part of this effort I also identified the root cause of the initial failure. And frankly I’m a little angry about it.
This was the failure I wrote about at the end of November in the post “When it Rains, It Pours!”. At first I thought that the primary 32µf reservoir capacitor had failed. Subsequent investigations showed that the capacitor was fine even though the 350Ω B+ dropping resistor had failed. I initially attributed the failure to a simple component issue. But upon further investigation I determined that the failed dropping resistor was due to excessive B+ current. And the cause of this excessive current was a power tube which developed an internal short.
Okay, tubes fail. Usually not in a manner that smokes other components, but failures are to be expected from time to time. So why has this failure left me a little angry? It’s because the culprit was a JJ 6V6S power tube. And this is the third JJ tube to fail and cause amplifier damage in one of my amps in the last six months. It’s not like I use JJ tubes exclusively and this behavior is more than a simple statistical anomaly.
So I am now suspecting that something is going on with JJ tubes. My first response is that I’m not going to be buying any more JJ tubes for a while. I don’t know if it’s a production or quality control issue, but it’s not worth my time and money to try and figure it out. For the foreseeable future, when looking for new production tubes, I’ll be buying Tung-Sol, TAD, Groove Tube, and maybe Electro-Harmonics.
I am also asking for some input on people’s experience with the JJ tubes they’ve purchased in the last couple of years. Is anyone else seeing excessive JJ tube failures, or is it just me? Please let me know. In the mean time I’m running some NOS 6V6GTAs from the 1960s in the Lacewood. And they sound really fine.
As always, questions and comments are welcome.
Hi Matt.
All of my new-production tubes are JJ. No problems up to this point. These include 6L6GC, EL34, KT77, KT88, EL84, 6CA7,12AX7 and ECC802S, and all have significant amount of hours on them. I use solid state rectifiers so I can’t speak to their rectifier tubes.
Hi Matt, happy new year to you and subscribers. I haven’t had any issues with my JJ GZ34S tubes on both the 300b SET and 6AS7 SETs of your designs I tried to follow for the most part. The Hammond power transformer failed early on in the 6AS7 SET blowing fuses which Hammond agreed to replace after a few tests. All good since cross fingers. The 300b has Edcor hardware which has been robust except for a little buzz in the power transformer which doesn’t bother me at the listening position.
Does Matt have a 300B design he’s made available?
I helped of Mark Huston many years ago with his Silver Dragon design. The full story can be found here: http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=2699
The forum thread contains a tremendous amount of detail on the entire project.
Over the years I’ve had several JJ tubes fail incredibly early. Enough that I similarly said no more, JJ! I’ve had good experience with current production Sovtek and Mullard. For 6CA4, US made NOS tubes are still plentiful and cheap, so no reason to purchase anything else. If a reasonably priced US NOS tube is available, I’ll buy it instead of Russian or Chinese production.
Rectifier plate resistors are also critical for very high voltage transformers. Something I learned the hard way.
In the last few months I have had some odd behavior with tubes in my lacewood build. I had a jj 5u4gb, JJ6sn7 and two JJ 6v6s. Build date was 10/21. From the first power on the JJ 6sn7 flashed briefly with no apparent issues. I just passed it off as being like some others issue with tube flash on power on. Then, approximately 6 months ago the amp blew fuse immediately on power up. Checking proved flash over on JJ 5u4gb. Replaced JJ 5u4 with a new EH 5u4. Amp powered up fine, no flash or blown fuse, however after about 30 minutes power trans was pretty hot. After some checking I decided to take out the EH 5u4 and install another new JJ5u4gb. Power up normal, no more pt heating. Replaced the flash on startup JJ6sn7 with nos ge. Better sound across the board and has many hours on it now. If I have any more 5u4 issues I will go to the rca 5u4 I’ve been saving. By the way Matt I love the Lacewood and both Marblewoods I’ve built.
Please refresh my memory. Did you use the Hammond power transformer or the Edcor? I’m curious because the Hammond has significantly higher secondary resistance. Just gathering data at this point.
Hammond 270fx. Also hammond 193 10 henry choke.
Personally, I think NOS tubes are the best – they are the “real deal”. All the others are imitations or interpretations of the original, usually US made tubes. A lot of offshore new production tubes are kind of a “crap shoot” – never know exactly what they are.
I agree that NOS tubes are generally the best option. The only condition is that they actually have to be NOS and not used. A lot of tubes which are sold as NOS are in fact used. And it’s impossible to know the history of those tubes.
However, there are some NOS tubes I avoid on principle. The coin based octal tubes are a good example. This design change was made at the end of the vacuum tube era in an attempt to make tubes more economically feasible. They also came with looser quality control requirements to keep the price down. I have had mixed success with these tubes; especially the RCA coin base variety.
Back in Jan. ’23 I ran into problems with 3 JJ rectifier tubes. Two EZ81s and a 5Y3. The EZ81s produced a shimmery high pitched noise. It sounded similar to the tube in this video…
https://www.youtube.com/watch?v=9uOx8JXSXWc
The other tube was a 5Y3 that arrived DOA.
Steve
This problem is especially common in 5U4s and 5Y3s as they age. Often in guitar amps where they are use in a less than ideal manner.
I had a problem with a JJ 5AR4 rectifier tube that was in a guitar amp I built. It is interesting to hear your story.