I have to replace some BUZ80 mosfet follower in a Melos amp. A 12AU7 drives a BUZ80 mosfet which drives a pair of 6KG6 /EL509, EL519. I found this mosfet which appears really great to replace the BUZ80. The mosfet is: STF4LN80K5
Crss is only 0.3 pf
Specs are here:
https://www.mouser.ca/datasheet/2/389/dm00179664-1798710.pdf
Is there some problems if I use this part ?
Thanks
Crss is only 0.3 pf
Specs are here:
https://www.mouser.ca/datasheet/2/389/dm00179664-1798710.pdf
Is there some problems if I use this part ?
Thanks
Not sure if it impacts whether its a good fit or not but fig4 (output characteristics) looks rather sub-optimal: the output impedance is low in common-source. BUZ80 looks much better in that the load lines are horizontal. Threshold voltage is a couple of volts higher but probably that's of no consequence.
The transconductance at 1.5A is merely 1 and rediculous at low currents. It will decrease the gain and generate lot of distortion. If 600v can do, The very low cost IRFBC20 is a better replacement.
If the MOSFET is to be used as a source-follower then yes you can use the STF4LN80K5 (you can use most any MOSFET). It may not stand out in a crowd of MOSFETs, but compared to any tube it has way more gm than your heart could desire. It will be sonically invisible.
Looks like a very decent MOSFET for this duty. The low capacitance is much more important than high Gm IMHO. But do note the Vds needs to be >80V-ish for those low capacitances.
As it seems not unanimous it will work correctly, is IXTP01N100D could be a better choice ?
ixtp01n100d ixtu01n100d ixty01n100d.pdf PDF datasheet. ALL TRANSISTORS DATASHEET. POWER MOSFET, IGBT, IC, TRIACS DATABASE. Electronic Supply. INNOVATION CATALOG. Service
ixtp01n100d ixtu01n100d ixty01n100d.pdf PDF datasheet. ALL TRANSISTORS DATASHEET. POWER MOSFET, IGBT, IC, TRIACS DATABASE. Electronic Supply. INNOVATION CATALOG. Service
That one's depletion mode - are you aware of the difference between that and enhancement mode in MOSFETs?
I have had to repair an identical Melos amp, with failed MOSFET followers. Virtually and MOSFET is fine in this configuration - it simply provides a low impedance drive to the screen grids, which are used as control grids in this topology.
A serious flaw in the Melos design (and it had many!) was the protection of the MOSFET gate. You should solder in a 10 volt Zener between the gate and the source, otherwise during startup - under the right conditions - the max VGS for the mosfet may be exceeded.
Generally, no. But enhancement mode generally have better specs. I prefer the FQP4Nx0 series of MOSFETs. Low capacitance and available in an insulated package.
After doing some more research, it seems this one should be the best of the best
TK7E80W
https://www.mouser.ca/datasheet/2/408/TK7E80W_datasheet_en_20161008-1099463.pdf
TK7E80W
https://www.mouser.ca/datasheet/2/408/TK7E80W_datasheet_en_20161008-1099463.pdf