Here goes..Good Evening All,
Dare one ask why???
To properly show their character the VFETS need +/- 28V, but will 'work' with anything from 26V to 30.
These amps can be fiddled to make sound with a 24V PSU (at least according to NP), but the results are nowhere near the/ his design intent.
The front end of these is a mildly reworked F5 and needs 1.5V of bias (anything less and its not going to properly drive the VFETS, anything more and it will start to get quite hot)
The CCS' for the VFETs need 2V across their regs , or these will drop out = sub optimal performance
The VFETS need 125+ mV of bias to reveal their 2nd/ 3rd/ 4th order distortion profile and sound like a triode
Maybe with many resistor value changes a sweet spot can be found where the above will all work with 24V.
Massively easier to fit new torriods that put out the correct voltage
...and then spend every weekday evening for the past 6 weeks tuning the thing to get the desired distortion / delicacy.
You've got to put the hours in tweaking the bias until the VFETS spring to life, and then find the spot where they reveal their character with the lowest achievable noise floor, it's a bit like tuning an old FM radio.
Actually quite far from easy, but it does now sound like an F5 that's had its output stage replaced with a pair of EL34
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