I received my ta26 from apos.audio yesterday 7-20-2021 - running stock buffer tube. Stock gain tube bass is quantity over quality, really sloppy, and the midrange is in your face. I tried a new production JJ, Tung Sol, and ElectroHarmonix 6sn7 and they all hummed crazy loud in the left channel. Swapped in a vintage GE and zero hum and way better sound. Chassis build is really nice. Buyers beware, rolling your 6sn7 tubes is going to be crap shoot.
ethrSo far nothing I've rolled into mine has had hum, unlike when using the same tubes in my DV where everything is a mess of 60/120hz noise in both channels without stupid burn-in.
It is interesting that the hum you are/were getting is in a single channel and stayed in that channel throughout the rolling of new productions. It makes me wonder if something was off with the amp you received (or if I just rolled a natural 20 with regards to the one I received).
Does the hum hold consistent when you roll a different 6AS7 in place the stock Chinese 6N5P while using the new prod 6SN7 tubes? I've never been overly impressed with the Chinese 6N5P and 6N13P (or really most NOS Chinese tubes), the consistency is just too all over the place.
Also, I know it is kinda silly to ask (especially so seeing you've found a NOS tube combination that doesn't hum), but does the hum hold to the same channel if you swap the RCA left and right? If it follows the swap, the problem might not be related to the tubes themselves.
ethrThis works for the Darkvoice so I assume it could for this amp too. This amp seems like a copy of the DV, and given the hum in the preamp, it has the same issues. I did the burn in trick with a new 6NS7 with the power tube removed on my DV amp. It took about 3 days straight to get rid of the hum. Only do it with the power tube removed since the amp stays a lot cooler. Despite being on for three days this is a small blip in the lifespan of a tube like that.
ethrThere is. This looks like an exact copy of the DV 336 SE and appears to be so on the circuitry side based on your issues. Look through all the DV threads and you'll see the same issue persistent across all samples and 6SN7 tubes due to wrong heater voltage in the unit.
FWIW, I have a DV and a Sylvania chrome dome 6SN7 that sounds wonderful, but even after a few days of burn-in still hasn't removed the hum fully. I replaced it with a RCA and it isn't as holographic sounding but has no hum.
ethrOk, final update. This is a fantastic amp and which tubes you get are going to determine the level of hum and how long they need to burn before they stop. Just know that going in. I've rolled 5-6 different tubes and the amp is HOF value, highly recommended. The only pattern I found with hum is the newer the tube the more likely they are to hum. If you run 600ohm Beyers you don't need to worry. I'm running T1 Gen 2 and I am in heaven.
ethrDarkvoice quality control issues are scary. Hope this is better made. Return/replacement is practically impossible for buyers living outside USA. Getting a faulty unit = money down the drain.
ethrMay I know what specific tubes you'd used and their characteristics? I just got over 10 hours on the stock tubes. Initially, music was distorted and I thought its broken but its sounding better and better.
MahimFirst time I hear this.. Had absolutely no problem with mine, and read about it extensively and definitely wouldn't have bought it if there were concerning news about quality controll. Its a great unit praised by thousands of happy users..