There are many different types . I have had many in my day .Currently I have which is considered the purest preamp type, Single ended . Which has several unique features . It is a Direct Heated Triode type completely Lundahl Transformer coupled 5 transformers,and 3 chokes and the little known 4P1L Vacuum tube
which is very Linear, plenty of gain to eliminate the need of another tube for additional gain stage like many indirect Heated tubes. A very detailed and
well balanced tube .it can be a bit microphonic in vibration if the builder does not
isolate the tubes and isolate and damp the power from the Audio output section properly .modern technologies like relay remote and 63 step Shunt attenuated- Khozmo type. just another twist for another Audiophile dilemma.
which is very Linear, plenty of gain to eliminate the need of another tube for additional gain stage like many indirect Heated tubes. A very detailed and
well balanced tube .it can be a bit microphonic in vibration if the builder does not
isolate the tubes and isolate and damp the power from the Audio output section properly .modern technologies like relay remote and 63 step Shunt attenuated- Khozmo type. just another twist for another Audiophile dilemma.