James of Von Saint Design is a bass lover like the rest of us, but even deeper his passion lies in vintage Ampeg SVT gear.He sent us Parts 1 and 2 of a 4-part You Tube series he made about the classic equipment.During loud transients and overloads this will produce an AC signal that far exceed the 12BH7 follower that has 220V on the plates.So when the follower grid is driven far over its own plate voltage it saturates on the positive half of the signal and thus takes over the BIAS voltage forcing it very positive.Mainly due to the output transformer primary inductance with respect to plate resistance..The 6146 is much lower in transconductance and is less sensitive to drive signal, thus needs a bigger voltage swing to drive than a 6550...The amp will produce roughly 225 watts , due to the screen voltage being too low.
They also came with 3-prong power cables, and no polarity switch.
The early driver circuit was not properly designed, therefore would blow the 6146B tubes on occasion.
The reason most 6146 SVT amps blow tubes and resistors is due to front end 12BH7 voltage amplifier is being fed from the 430V node.
The diode will clamp the current in the 22ohm screen resistor to 30m A, so preferably the plate resistor will blow...since the plate resistor is acting as a "fuse".
Plate resistors should be kept off the circuit board by approx 1/2" min to prevent PCBA burning.