(to be translated...)
We offer some brands of output tubes as UralTone SQ classified. Its possible to choose from Low (1), Low medium (2), Medium (3), High Medium (4) ja High (5) -classes. As extra we offer HiFi classidied tubes with tigth tolerances as well as tubes for certain amplifiers (for example Classic 30). These are drop in selected tubes by right bias value on stock / nmodified amplifier. All SQ tubes are tested and matched by tailor made UralTone tube tester and driven in for needed time before measuring.
Classification works following:
1. (Low) Falls to distortion on on smaller level than medium. Low headroom.
2. (Low medium) Falls to distortion on on tad smaller level than medium. Bit lower headroom than normal.
3. (Medium) Normal tube with nominal characteristics.
4. (Medium high) Distorts with bit higher signal. Increased headroom.
5. (high) Distorts with high signal, high headroom.
Example: If your amplifier starts to clip on output when volume is set to five with high classified tubes, it will distort when volume is set on four on low classification tubes. This applies only with fixed bias amplifiers (almost all Fenders and Marshalls). These amplifiers requires bias adjust when outputtubes are replaced and the classification is changed.
Certain cathode biased amplifiers (eg. Vox AC30) are factory set on high bias. We recommend to select low- or lowmed tubes for increased durability of the output tubes.
We recommend to use medium tubes on Mesan amplifiers if the bias is not set when tubes are replaced.
It's possible to save by using certain callsified tubes. By then tubes are possible to replace by same classification when tubes are replaced. It's possible to buy spare pair or quad etc.