Question on "rails"

[Bufo Bill]

I see many accounts of fault checking on, for example, an amplifier and the "rails" are often measured. What are the rails? What is their function? I am of course a complete beginner, so any help with the vocabulary would be most welcome.
Many thanks from Bill.

[Station X]

The power rails, or supply lines.

On British valve circuit diagrams the positive HT (High Tension) rail generally runs horizontally across the top of the page and the negative HT line across the bottom of the page.

Equipment needing more than one voltage may have several supply rails. +24V, 0V and -24V by way of example.

[G6Tanuki]

In valve circuitry, the "rails" - are often known as:

A+ or A rail - the supply to the valve heaters.

B+ or B rail - the high-voltage HT supply to the valve anodes.

In some instances you may come across a C-supply, which is a separate negative-bias supply generally fed to the output valve(s).

[Bufo Bill]

Cheers thanks for clearing that up guys
Bill

[M0FYA Andy]

Originally Posted by G6Tanuki

In valve circuitry, the "rails" - are often known as:

A+ or A rail - the supply to the valve heaters.

B+ or B rail - the high-voltage HT supply to the valve anodes.

In some instances you may come across a C-supply, which is a separate negative-bias supply generally fed to the output valve(s).

This is very much American terminology, not traditionally used on British circuit diagrams.

Andy