which are the "cathode follower" positions in the mark?`

[boogiemon]

Anybody know which pre-amp tubes in a Mark are in "cathode-follower" positions?

i'd also like to know why tubes in those spots need to be more rugged.

tia.

 

[>Photi G<]

Cathode follower tubes only appeared in the mix stages of the Mark IIA and IIB. This was in the V2 position. These tubes need to be more rugged because on a normally coupled preamp stage, the cathode is biased at a rather low voltage, between 1 and 3 volts. In a cathode follower stage, the voltage passing through the cathode is significantly higher; in the IIA, this is around 250 volts. Also, V2A and V2B are directly coupled gain stages, which means that the capacitor at the plate of V2A is omitted, and the full plate voltage of that stage is fed into the grid of V2B. So when dealing with these unusually high voltages, a high grade tube is required.

No other Mark amps after the IIB used a cathode follower stage.

 

[boogiemon]

great. thnx.

Cathode follower tubes only appeared in the mix stages of the Mark IIA and IIB. This was in the V2 position. These tubes need to be more rugged because on a normally coupled preamp stage, the cathode is biased at a rather low voltage, between 1 and 3 volts. In a cathode follower stage, the voltage passing through the cathode is significantly higher; in the IIA, this is around 250 volts. Also, V2A and V2B are directly coupled gain stages, which means that the capacitor at the plate of V2A is omitted, and the full plate voltage of that stage is fed into the grid of V2B. So when dealing with these unusually high voltages, a high grade tube is required.

No other Mark amps after the IIB used a cathode follower stage.