CAJames
Seasoned Member
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"I've run every red light on memory lane."
Posts: 2020
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This has been a very interesting day....and it isn't over yet.
I started out by going back to the 53KU rectifiers, which sounded really good. More air and more space, but slightly less bass compared to the GZ33. Then I added one of my favorite input tubes from the UFOs, RCA black plate 6CG7. For those unfamiliar, the 6CG7/6FQ7 tubes are 9 pin tubes with the electrical properties of a 6SN7. You can use them in place of a 6DJ8/6922/ECC88 without an adapter. They made the sound even better, but I figured I should try a 0D3 instead of a 0C3 in front and wow. With the bias switch at high the sound was just amazing. Huge sound stage, tons of detail, all the bass I could want (or expect from my 6 1/2" single driver speakers) and just the most living, liquid sound I've ever heard.
I could have stopped there, but the 6CG7 was so good there was another tube I wanted to try. I picked up some ECC40 tubes to try in my (non-Decware) 300B amp. They are an early attempt to miniaturize (i.e. make cheaper) the 6SN7 and they have a funky 8 pin English base. But you can get adapters for either a 6SN7 or 6DJ8/6922/ECC88. They were too warm and rich for the 300B amp, but I thought they would play well with the '25s and I wasn't disappointed. They sound like the 6CG7, but are more dynamic and with more bass. The sound stage is still huge left/right and up/down but has kinda collapsed front to back (which was never great in my room) so that is a bit of a downside. I'm not sure how these are going to play for the long run, but right now the sound is amazing.
Re: break in. For the last few days the sound has been very consistent on my '25s and (knock on wood) I feel like I'm through the weirdness. I'm not a patient person so I like to run new gear overnight to get it broken in faster. And when I do that with amps I run them pretty hard, both by playing them louder than I would ever listen (I play them into a dummy load and set the volume right below clipping) and also going with more aggressive material. IMO what new caps really need are transients, and harmonic complexity. I play a lot of big, modern orchestral music and I have a "burn in" track from an old Stereophile test CD that is a bunch of people pounding on pots, pans, drums and other noise makers plus electronically generated low and high frequencies that I run for a couple hours each night. I also have some Tibetan singing bowls albums that I would listen to when I needed to chill out after a bad day at work, but after Steve said they were good for breakin I mix them in too. To me they sound like tuning forks (pure tones) rather than something harmonically complex, but whatever. So I play the amps for 10 or so hours over night then turn them off for 3 or 4 hours in morning to cool off. This worked really well for my UFOs and it seems like I worked equally well for the '25s, but JMO/FWIW/YMMV and all that.
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