rebranding TAD rejects?

[maxkracht]

I just finished building a Princeton kit for someone which came with a pair of very microphonic "electron tube" brand chinese 6L6's. I noticed the word TAD marked on the base and was wondering if these could be Tube Amp Doctor tube's that didn't pass quality control or possibly just the same factory using the same base. Curious if anyone had any incite. I don't have any TAD tubes to compare with.

[FUCHSAUDIO]

It’s interesting to note that the Ruby 6L6 also comes from the Shuguang plant, which is Chinas largest tube maker. They build for many companies. I noticed their bases also say TAD. My understanding is they make different grades of tube, as well as having different grades of QC. I suspect those are the lowest grade and possibly low-grade rejects. In my experience, tubes labeled like that fail much quicker than others. Maybe they just use those bases on everything now. TAD claimed they had their own production line at the factory. Maybe not ?

[danlad]

Hadn't noticed the TAD on the base but I did get a couple from RS Components fairly cheaply as tester valves and noticed they looked identical to the naked eye to the TAD 6L6, but rated at just 23 watts on the website, so maybe they are downrated TAD rejects?

[danlad]

But just checked the RS website and even their photo of their 6l6wgc has TAD writ large on the base!

[maxkracht]

Interesting. I guess it is possible that TAD is some kind of internal factory code, but that seems less likely. Those tubes listed on RS are pricier than I would have assumed, so maybe these were rejects of rejects... Optimistically, they are included in amp kits as a precautionary measure in case something is wired very badly and not trying to get one over on their customers. They did work long enough for me to confirm the amp was mostly functional, then spend 30 minutes troubleshooting errant noises before plugging in a proper set of tubes and realizing there were no problems.