Four Ten
The "Four Ten" almost needs no introduction - based on one of the greatest and most famous guitar amps of all time - the "5F6A Bassman".
40 Watts into four 10" speakers with bass, middle, treble and presence controls, the 5F6A was the final evolution of the "tweed" series of amps.
When Jim Marshall wanted to introduce his first guitar amplifier he made an almost exact copy of the 5F6A and the DNA of this circuit lives on in many new tube amps today.
The "Four Ten" has a fortuitous combination of low gain 12AY7 preamp, more "modern" "long tailed pair" phase inverter and still too wimpy power supply providing plenty of sag.
For comparison the Marshall amps evolved from this circuit with a beefier power supply (for less sag) and a higher gain preamp - you can get closer to this sound by swapping the 12AY7 for a 12AX7 whenever you wish.