Just be careful where you stick your fingers...
Well, I managed to do it, and it all went well. Getting a zero reading was impossible, but I think I got within one.
In any case, the proof is in the pudding, and the RCA tubes are a major improvement, making the bass a little more robust and, importantly,
adding some warmth and smoothness to the upper mids (and highs), so my 009s sound extraordinary with my 007t/ii amp.
It's a superb combo in my book.
Yep, a matched set of 4 RCA cleartops from tube depot ($239).
I was surprised how major of an improvement it is. I've done lots of listening at pretty high volume levels with no strain that I can hear.
The SR009/007tii combination is really special, with no fatigue even on the popular or 60's music I listen to.
The speed of the sound, with lots of separation in a fast moving series of drum taps, is amazing and very satisfying, and what I think only electrostatic phones can do.
There is gobs of detail, but not hyped up, just natural detail.
It's sweet and insightful and delicate; I can hear what sounds like the fullest amount character of each instrument note and vocal I ever heard on headphones or speakers.
I sometimes think it's bass light, but then some big deep bass note will startle me with its impact. Bass transparency is as good as I have heard it; this not any sense of
subwoofery bass pumping; the bass sound is full of bass details, and it is there and then it is gone with no annoying hangover.
Here are some photos from my surgery on my Stax 007t/ii amp to install the RCA cleartops and perform the rebiasing. I can't emphasize how gorgeous the sound is with my SR009 phones. I was surprised at how good it is and how it perfectly targeted the treble area of the 009 and made them evenhanded from top to bottom frequencies and added overall refinement. The improvement was striking.
Very Good info on this thread! The trimmer adjustment tool can be ordered from Newark Electronics.
RCA clear top 6FQ7/6CG7 tubes from the 60's, 70's (NOS) sound the best, but are hard to find.
Tube World has pairs every so often, but they sell fast, so do not delay.
NOS tubes are like antiques, so buy without hesitation, when you find them, or regret it!
I suggest buying up a lifetime supply NOW!
The STAX amps now come from the factory with Russian Electro-Harmonix tubes, which I find "bright".
This is where the "false rumor" that the SR-009 is 'bright" sounding comes from IMO.
I own the SRM-T1S and SRM-006tS amps.
I also own the SR-009, Lambda Nova Signature, and SRX MK3 headphones.
Once warmed up, and playing music, for about 2 hours, the STAX amps match up to, or beat, the $6,000+ tube amps IMO.
The RCA tubes last about 4 to 5,000 hours vs 2000 hours for EL34's.
You should used balanced (XLR) cables, and a good CD/SACD player, computer, or phono for optimal sound!
PRO XLR cables that use Mogami or Canare wire are best. They are inexpensive. Avoid expensive audiophile XLR cables, they will not sound better IMO.
STAX are, and have always been, the best headphones! ENJOY!