How to Play the Trombone
Playing a tenorbass trombone or bass trombone

When a valve is used the slide positions are longer (farther) than on an instrument without a valve.
For example, on an instrument with an in-line double rotary valve, if valve #1 is an F attachment and valve #2 is a G♭ attachment, what will happen if a sound lower than B♭ is played? Take a look at the position diagram.

When set to F, the slide is reduced to six positions over the entire length of the slide. Using valve #2, or both valve #1 and valve #2, will similarly change the location of the slide positions. It all depends on how the instrument is played, its specifications, and its settings, so it is best to use a tuner or the like to confirm your own playing positions.

Theoretically, a tenorbass trombone should normally be capable of playing as low as C three octaves down from middle C (a minor seventh lower than pedal tone B♭). Some manufacturers have released instruments where a half-tone can be taken from the F attachment, making it an E attachment. In this case, the lowest note would be different.
A bass trombone with double rotary valves and equipped with an F attachment and G♭ attachment should theoretically be capable of playing B♭ a further major second lower (an octave lower than pedal tone B♭).
In either case, the slide will have a larger range than the normal seven positions.

It is notoriously difficult to produce the pedal tone (fundamental tone) with a trombone. This is not the case with a tenor trombone.

The position chart

A tenorbass trombone has only a single valve (F attachment), so B♭ and F on the position chart can be used as shown.

The positions from 9th harmonic series H to 12th harmonic series F are shown to the right.

The positions from 9th harmonic series H to 12th harmonic series F are shown to the right.

All notations are actual notes, and the numbers in parentheses show typical switching positions. Note that there are many switching positions in the high-tone range, and others may be used to play this. For any other note, you can use the same position as the note one octave below it.