#1 More buffers
Posted: Fri Feb 05, 2021 6:48 pm
I want to have a play with some buffers, for driving output stage grids (6b4g, 300B, 211), possibly into grid current. I'll try pentodes, but would also like to try some FETs. But which ones? I think I'm looking (in valve terms) for high transconductance and low Cag. Which translates into (in transistor terms) high Gfs and low Crss.
MJ used FQP1N50, which are obsolete.
Ale Moglia (Bartola) tested STP3NK60ZFP, DN2540, IXTP08N100D2, and preferred the STP3NK60ZFP which has also protection diodes.
Should I just pick one and have a go, or is there a firm favourite. It's not quite as easy as using the data sheet number, because the transconductance in particular seems to fall off at low current. I should probably do a spreadsheet, unless someone has been there before me and can recommend something?
If anyone is wondering how this fits into the PP 6b4G project, it is part of that. Or at least that that would be what I would use for listening to the effect of the buffers in circuit, in the first instance. I also want to see if driving ITs with such a low impedance brings benefits.
MJ used FQP1N50, which are obsolete.
Ale Moglia (Bartola) tested STP3NK60ZFP, DN2540, IXTP08N100D2, and preferred the STP3NK60ZFP which has also protection diodes.
Should I just pick one and have a go, or is there a firm favourite. It's not quite as easy as using the data sheet number, because the transconductance in particular seems to fall off at low current. I should probably do a spreadsheet, unless someone has been there before me and can recommend something?
If anyone is wondering how this fits into the PP 6b4G project, it is part of that. Or at least that that would be what I would use for listening to the effect of the buffers in circuit, in the first instance. I also want to see if driving ITs with such a low impedance brings benefits.