TAD Tube Amp Doctor 6550A, Matched 6, Premium Selected

NEW VERSION: Since Sept. 2010, the TAD 6550A-STR has been manufactured with a stronger and exceptionally pure anode material combination. In conjunction with the extended TAD burn-in and formating process, the 6550A-STR reaches an outstanding consistency and stability and outperformes even the 6550C -C-. 
This makes the 6550A-STR withstand even the most critical application like e.g. the Ampeg SVT.  (Fits only without the tube retainer)

The TAD 6550A-STR is a true remake of the vintage GE 6550A with a heavy, straight glass envelope, polished metal base and the authentic triple getter construction. A balanced tube, known for its incredible bottom end and rich mids. Smooth, liquid bass, natural sounding tone and a wide open character make this tube extremely popular for bass guitar amps and High End Hi-Fi applications. 
The ratings of the TAD 6550C-STR meet or exceed those of the classic 6550A tubes. It performs superbly in any application asking for 6550.

Q: When does a power tube become a Premium Selected power tube?
A: All power tubes labeled Premium Selected have passed the following tests:
- Plate Current (PC) and Amplification (TC)
- Low Noise Test
- Microphonic Test
- Sonic Tests
- Shock Tests
- Listening Tests
- Shorts & Leakage Tests