Avoid this company like the plague. They sent me faulty tubes. I understand this can be a touchy and debatable subject, but it was their approach that insulted me and their product damaged an original 80s JCM 800. They acted like they could care less. Below is the way they will talk to. Me: Good Morning, I purchased 2 x El34 Groove tubes from you and they stopped working in 3 months. The tubes burned out my 1984 Marshall JCM 800 that I have to put into repair. I would like to know what you can do for me as I need new tubes and I have to pay the cost of repair. Them: Hello, We are sorry to hear of the problem with your Groove Tubes EL34M Duet (1x 296806).Tubes are subject to blown if they are not properly handled. Are they been installed by an expert? Does the amp was biased properly after the installation? In any case the warranty does not cover improper use of the tubes. Please let us know and do not hesitate to contact us in case you have further questions. Me (getting angry): The tubes were tested in two different fixed bias amps (1969 Sunn Solarus and 1984 Marshall JCM 800), both running on EL34s. Two other sets have been used and tested (Sovtek and Svetlana), without an issue. At least one of the tubes is defective and caused electrical problems in both amps and now my Marshall has a burnt tube socket. I have been doing this for 20+ years. Kindly advise how your company will approach this situation. Them: We have forwarded the information to the relevant department in order to discuss different possibilities to resolve this issue. Once we have received the required information from them, we will be in contact with you. In the meantime could you please send us a video to show our experts the problem occurred? Should you have any further questions, feel free to contact us at any time. Me (getting angrier) If you mean by video putting these tubes back into one of my amps and turning it on then no, I cannot do that. Like I said, it already damaged my Marshall. I would be happy to send you pictures of the faulty tube as you can clearly see the damage on the prongs, glass and sealant around the plastic base. Them: In this case the pictures are no longer needed as I received an answer from our technicians. In such cases you always have to check the Bias when putting tubes in different sorts of amps. Fixed Bias has nothing to do with checking Bias. And fixed Bias does not indicate that you can put in every set of tubes without damaging the tubes or the amp. Fixed Bias only means that you could put in tubes with the same rating as the original tubes (if you would be able to get some of those).One should always check the Bias after replacing the (power-) tubes !From this description seems that you did not check the Bias accordingly. Since the the 6 months warranty period for tubes is over, you can send us the tubes and we can check if they are defective. If so we can forward those to the service partner and maybe they will replace it. But in regards to the amplifier we are not responsible for the damage. If you have any further questions on the matter please send a direct reply to this email. Me (really angry) The tube is faulty and caused damage to my amp. The EL34 tubes are the same/similar rating and my amp has been at the same bias setting for over 20 years and I have never had a problem. The biasing variance is minimal under these circumstances and I run the tubes at low bias settings for a cleaner sound. This is unacceptable and not how a company should approach their customers and you shouldn't assume your customer doesn't understand how to operate their equipment. I will be leaving a bad review and I will never purchase from your company again.