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TubeAmpDoctor 6V6GT-STR - 2 weeks in...

Posted by DewDude on May 17, 2017 at 17:36:38:
So a couple of weeks ago I had a screen short in a tube (I did confirm it was a screen short), it was the second tube out of a non-matched quad I had as a backup. They were JJ Tesla 6V6S that came in the amps when I bought them in 2010. I used them for about three years with no issues when I decided to swap in a quad of the Reflektor 6P6S I had laying around. I never tried running them because my amp runs 340V on the plates and 330V on the screens...which is insane in my book. I assumed those tubes would just start arcing and cause all kinds of problems.

I wound up running them for another couple of years. They sounded ok at first, got better with age; then I guess I just "got used" to them. I was never disappointed with the sound. One of those developed what one guy called "hot cathode", for whatever reason the cathode was getting hot. I don't know how long it took me to notice, the thing seemed to run fine in my amps; but I pulled the JJ's out of my box and stuck them back in. Within 4 months I had two failures; one started arcing internally, one shorted and took out a power supply resistor. I limped on the 3 good reflektor tubes and a chinese 6v6gt we had in stock at work for a while. It sounded ok...but I ultimately wound up thinking about it too much and decided to look at the suggestions everyone had given here, do a little research, and buy a new quad sooner than later. In the long run the tubes were probably better than losing it at the craps table next month.

I ultimately decided to still put gambling in the mix (since I'd been planning this crazy trip out west that includes a few days in Vegas) and decided to give the TubeAmpDoctor tubes a try. Most everything I read told me they were pretty durable tubes that wouldn't mind the insane voltage of my amps, and most people said they had a great tone. But I don't recall reading many, if any, reviews of the tubes from a hi-fi perspective. I didn't even think the 6V6 tube would have been popular for guitar amps. I picked up a matched quad because it wasn't much more than buying 4 unmatched tubes; I have to my knowledge never run what could be considered matched tubes. It doesn't care, I've seen them run with just one tube in the output stage.

My setup are a pair of Motorola HS-619 monoblocks driving a pair of Ohm Model Ls, with the upgraded woofer...that I made sure I had a desk big enough so I could sit in front of them. I'm using a Yaqin MS-12B for a preamp, it's 12AU7 stage as well as the 12AU7 stages in my Motos are running Sylvania 5963s. I'm not a purist, so I'm not only using the tone controls on the amps but I've got a Sansui SE-8 sitting in the chain, driving that is a Little Bear P5 thing I picked up from someone for cheap. Think MusicalFidelity X10D clone but using a small pentode providing gain (that I don't need anymore but oh well). The source is a SMSL M8 DAC I'm feeding from my PC.

So the only output tubes I've run for any length of time have been the JJ 6V6S and the Reflektor tubes; I enjoyed both, but jumping from the Reflektor back to the JJs made me notice quite a few things I didn't the initial time I ran the tubes. The Reflektor's sounded more like what I'm used to from vintage amps; slightly creamy midrange with nice highs and deep lows, but I always felt the lows were a little "soggy" and didn't hit quite as "hard" as I was used to. The JJs had a tight punchy bass, but the midrange was much more tame and the highs seemed bright. Complicating this is fact the only information I can find lists my OPT secondary as "6 - 8 ohms"...and I think these Ohms are rated 4 - 8, "depending on where in the curve you measure". Does it matter? I don't know, it might change the overall loading on the tubes and cause small changes...the math says it does. I just care more about whether I'm enjoying my listening experience without destroying my iron and/or tubes.

So in come the TAD outputs. As I mentioned earlier, I never specifically picked up matched tubes for these amps. I've worked on amps where mismatched tubes will cause all kinds of problems...but these things literally don't care. But I decided this go around I'd just pick up a matched quad. I've read they match these at the factory, and all four boxes came pre-taped together and the labels indicated that both plate current and amplification were exactly the same in all four. I stuck them in and turned everything on, since nothing started smoking or arcing I settled down to listen to some initial impressions I'd later disregard after the tubes got "burned in a little".

The initial impressions seemed mostly psychological, "I swear these things sound more balanced". For the last year or so, for absolutely no reasons I could discern from measuring voltages; my left amp was just a touch louder than my right amp. It was easy to compensate for, but I chalked it up to something I was too lazy to test (like pulling every cap and testing it), or just the fact I'm using my speakers in the worst possible conditions for which they were not made for. I didn't have that problem anymore...which made no sense since I'd done things like swapping preamp and output tubes around in various configurations in the past. The "sweet spot" is now easier to achieve and the soundstage sounds more defined. Tone-wise these remind me of what I loved about the JJ tubes and what I love about the vintage tubes. It's actually a very similar sound to when I ran a Reflektor and JJ as a pair in each amp. I liked them immediately, the bass was tight and punchy, the midrange has just the perfect touch of vintage cream without sacrificing "detail", the highs were crisp...crisp enough I found myself knocking a couple of dB off the top end. They sounded great...I just needed to let them burn for a few more hours, every night, for two weeks.

I can't really say things sound much different, maybe these tubes were already "burned in"...maybe that's a myth and the only reason I noticed it with the Reflektor tubes was I just became "adjusted" to listening to them; of course I've barely broken 50 hours on them. I'm still impressed with these things, they perform fantastically. Patsy Cline hasn't been with us for 54 years; but when I listened to the SACD of the Greatest Hits, I swore she was in front of me...yeah..the JJ tubes put her there too, but these put that sweetness back in her voice.

I really like them, I'm glad I bought them.

Physically the tubes look to be well made. The guts have the more traditional slightly curved plate, except the entire assembly looks a bit "fatter" than what I'm used to seeing, plus they have some fins. My amps are pretty old and the sockets are pretty worn, but these actually took some force to insert. I don't know if that was center pin or if it was the actual pins, but they felt very solid going in. I also spied insulation on some of the leads going down to the base..I didn't spend very long trying to figure out where exactly it was going to, I just wanted to get them in. I also noticed what seemed like a pretty quick filament warm-up time, they to full brightness before any of the other tubes.

Sorry for the novel, thanks for reading.