Depends on the gain of the FETs. If they can more than double the current for a 2.7V increase in gate voltage, you will get your additional current. That means it is a balance between Vt and Gm. A high gm transistor will therefore turn in a lot of current for a rise equal to Vt, which the circuits in 39 and 40 will do. Hence, I'd expect the one I posted would in fact do more as they use vertical FETs, not laterals, and have a Vt around 3V and a gm of 21S. In principle that 3V would drive 60A - but it takes a 10V drop drain to source to achieve that.
Update (2):
The current imbalance between the two output FETs I mentioned is entirely due to the non-ideality of the bootstrap "constant current" source, as I indicated. Of course the original circuit had a mismatch between the upper and lower impedances, the 220 ohm bootstrap resistor being in parallel, effectively, with the 470 ohm load resistor.
As the circuit works with less driver current, the bootstrap resistor was changed to 470 ohm with an improvement in the balance.
As you would expect, a proper constant current source eliminates the problem completely, but would need a 5th transistor and a higher supply rail so as not to limit the available output voltage. Ini seeking to avoid adding transistors I even simulated a 10k load resistor running from 270V. Even that did not balance the currents to better than about 2:1. A compromise bootstrap using 2x 1k resistors fed from a 70V rail, which can be obtained from voltage doubling a 35V supply, gets very close.
The current imbalance between the two output FETs I mentioned is entirely due to the non-ideality of the bootstrap "constant current" source, as I indicated. Of course the original circuit had a mismatch between the upper and lower impedances, the 220 ohm bootstrap resistor being in parallel, effectively, with the 470 ohm load resistor.
As the circuit works with less driver current, the bootstrap resistor was changed to 470 ohm with an improvement in the balance.
As you would expect, a proper constant current source eliminates the problem completely, but would need a 5th transistor and a higher supply rail so as not to limit the available output voltage. Ini seeking to avoid adding transistors I even simulated a 10k load resistor running from 270V. Even that did not balance the currents to better than about 2:1. A compromise bootstrap using 2x 1k resistors fed from a 70V rail, which can be obtained from voltage doubling a 35V supply, gets very close.
Install MOSFET instead of Darlington. Change the Bias.
https://www.diyaudio.com/forums/attachments/solid-state/660785d1517841427-jlh-d16-jlh-d16-png
https://www.diyaudio.com/forums/attachments/solid-state/660785d1517841427-jlh-d16-jlh-d16-png
