Can I use this for mosfet follower

[legarem]

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

 

[abraxalito]

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.

 

[U130421]

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.

 

[Merlinb]

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.

 

[SemperFi]

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.

 

[legarem]

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

 

[abraxalito]

That one's depletion mode - are you aware of the difference between that and enhancement mode in MOSFETs?

 

[LVQ]

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.

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.

 

[legarem]

That one's depletion mode - are you aware of the difference between that and enhancement mode in MOSFETs?

Not really. Depletion vs enhancement, does it really matter ?

 

[Fenris]

Generally, no. But enhancement mode generally have better specs. I prefer the FQP4Nx0 series of MOSFETs. Low capacitance and available in an insulated package.

 

[legarem]

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