Dual Triode Grading System: All RAM Tube Works dual triodes are tested and graded using our proprietary tube testing computer developed by Roger A. Modjeski. The following grades are available in all dual triode types. Super Low Noise (SLN): Quite simply the industry’s quietest tube, suitable for the finest phono stages as well as any other critical application. Low Noise (LN): A superior tube especially tested for today’s quality line stages. Standard Grade (SG): Our most economical tube, yet still a product of selection. In fact, it easily outperforms the best tubes offered by other companies.