I have a lot mjl21194 and mjl21193 transistor.
Can I use instead 2sk1058 & 2sj162
Thank You ...
MJL's are BJTs' not lateral MOSFETs. You will need another drive stage to get enough current to drive the BJT's then it's not an FX8 anymore. I was able to modify circuit to accept vertical MOSFET (IRFP240/9240) with addition of a single Vbe multiplier (so technically an FX9 hexFET). MOSFET's are voltage drive not current drive.
hi Mr. Mile, maybe i could get this PCB in PDF file? or where i can find it? i've be grateful for your help
Attachments
FX8 with hexFET and BD139 Vbe multiplier
I got rid of the flying leads on the main output hexFETs by crossing the Drain and Source pins so that they could be connected directly to the board as made for GSD pinout. I also switched the MPSA42 for a BD139 Vbe multiplier so that it was easy to bolt to the top of one of the hexFETs. I set the bias initially at 250mA and then reduced it to 150mA and it sounds great. The bias is stable with this setup. Much more compact now without the flying leads. Other changes include putting the LTP in thermal contact and binding them together with shrink tubing.
I got rid of the flying leads on the main output hexFETs by crossing the Drain and Source pins so that they could be connected directly to the board as made for GSD pinout. I also switched the MPSA42 for a BD139 Vbe multiplier so that it was easy to bolt to the top of one of the hexFETs. I set the bias initially at 250mA and then reduced it to 150mA and it sounds great. The bias is stable with this setup. Much more compact now without the flying leads. Other changes include putting the LTP in thermal contact and binding them together with shrink tubing.
Attachments
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Mr. Mile,
Isn't +/-55V is a bit high for single pair o/p? and can you post sch with 2 pair o/p? and also its supply voltage and power in 4 ohms?
reg
prasi
B863 / D1148
Hi Mile,
The above transistor can be used in any amp of yours?
I have many in hand
Regards
Hi Mile,
The above transistor can be used in any amp of yours?
I have many in hand
Regards
I got rid of the flying leads on the main output hexFETs by crossing the Drain and Source pins so that they could be connected directly to the board as made for GSD pinout. I also switched the MPSA42 for a BD139 Vbe multiplier so that it was easy to bolt to the top of one of the hexFETs. I set the bias initially at 250mA and then reduced it to 150mA and it sounds great. The bias is stable with this setup. Much more compact now without the flying leads. Other changes include putting the LTP in thermal contact and binding them together with shrink tubing.
Nice work,
Regards
Thanks! Should this variant be renamed FX9H? 🙂
I think it is compact enough for me to put two amps facing each other transistor-to-transistor on the same heatsink and maybe add a small fan 50mm to cool the heatsink.