Ruby 12AX7AC5 HG Preamp Vacuum Tube
The Chinese Made Ruby 12AX7AC5 HG tubes (made at the Shuguang Factory) are popular with Marshall owners (and also similar amps) for their gain and bite. They are the tubes that are already found in a lot of amp brands on the market for their sound and reliability.
More pronounced mids to high mids with a tight bottom end and higher gain. These tubes work well in amps that have a large bottom end.