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.