The lower voltage zeners should be fine since the Vgs to current curve look similar enough to that of the IRFP240 (at least on the datasheets).
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@freebee and @Dennis Hui
Thanks for clarifying. Since the OP stated IRFP049, I couldn’t find an N channel MOSFET, it is indeed IRFP048 as seen in his picture.
Best,
Anand.
Thanks for clarifying. Since the OP stated IRFP049, I couldn’t find an N channel MOSFET, it is indeed IRFP048 as seen in his picture.
Best,
Anand.
Anand, you did ask the pertinent question since there was a typo in the part number. So everybody helped. 
Digikey lists this part number "IRFP048N" as "Obsolete". No longer manufactured... How long ago did you acquire them? The F6 parts kits have been out of stock for at least 3 months now. I'm waiting with bated breath for them to come back in. A consideration for substitutions might be to compare the "input capacitance" of the devices. If it is too high, it will require more current drive to overcome the input capacitance and may suffer some high frequency roll off internal to the circuit... The IRFP240 also comes up as Obsolete, no longer manufactured at digikey.
Story of my life, there is always some component to any project that is made of unobtainium...
Story of my life, there is always some component to any project that is made of unobtainium...
Sometimes you just need to look for the "PBF" (lead-free) version: For example, IRFP240PBF is in stock at both Digikey and Mouser.
Ahh. the IRFP240PBF is readily available. My myopia. Lead free, seems to be the way to go, these days.
look for any, ignore suffix
I mean, important is "IRFP240", ignore rest
I mean, important is "IRFP240", ignore rest
Donaldspace, The store has the mosfets and Zener set in the Active Devices section. I have some leftover parts, got the transformers from cable solutions and the jfets from punkydawg’s store ebay.
https://diyaudiostore.com/collections/mosfets/products/f6-transistor-kit
https://diyaudiostore.com/collections/mosfets/products/f6-transistor-kit
Does anyone know off hand what the transistor bolt spacing is for these boards? The Universal mounting spec doesn't list this amp.
Yes but I am not using UMS heat sinks and the F6 is not listen in the UMS mounting spec. I'm sure the boards fit somewhere on those heat sinks, but the spec doesn't list where.
Do you just need the measurements? I have a bare board I can measure for you.
Measurements would definitely be a big help. I'm trying to get my chassis designed before the boards get there if possible.
See if this helps. I’m happy to get others if you need them.
I’m trying to get these from the center of the holes. The 4 sets of vertical mounting holes are 40mm apart. The 3 sets of horizontal holes are 80 mm apart. Each hole about 5mm from the edge of the board. Reading from left to right, the first hole for Q1 is around 99mm from the left edge of the board, 110.3mm to the third hole. Reading from right to left, the first hole for Q2 is 19mm, the third hole is 30mm from the right hand edge of the board.
one more thing, the Q1 and Q2 pads are about 1mm closer to the edge of the board than the board mounting holes.
I’m trying to get these from the center of the holes. The 4 sets of vertical mounting holes are 40mm apart. The 3 sets of horizontal holes are 80 mm apart. Each hole about 5mm from the edge of the board. Reading from left to right, the first hole for Q1 is around 99mm from the left edge of the board, 110.3mm to the third hole. Reading from right to left, the first hole for Q2 is 19mm, the third hole is 30mm from the right hand edge of the board.
one more thing, the Q1 and Q2 pads are about 1mm closer to the edge of the board than the board mounting holes.
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Thanks, I'll add those into my drawing in the morning.
I appreciate you taking the measurements for me. I won't build anything unless I draw the whole thing in CAD first, force of habit.
I appreciate you taking the measurements for me. I won't build anything unless I draw the whole thing in CAD first, force of habit.
I believe the two source resistors being different is what creates the distortion characteristics. You can run it with .47 on both but It will likely sound a little bit different.
For reference, my experience starts with the Green LED bias network as captured by jreel in https://www.diyaudio.com/community/threads/f6-illustrated-build-guide.277850/post-7286651
That helps bring up the bias current to a stable value in a more timely fashion. I also like the (now discontinued) FQH44N10 Mosfets. They happen to like higher voltage and bias current. I have taken advantage of this. Power rails are +/– 26.5V and bias is 1.95A, as recently re-adjusted and confirmed.
The next part may muddy the waters more than some builders want:
The source resistors in the output stage may be split into two values – one above the connection with the 1000 uF capacitor and one below. This possibility is discussed in Nelson's original article on the F6, back when it was still using the mostly unobtainable SemiSouth devices.
I have set R1 to a sum of 0.40 Ohms, 1% below the cap junction + (0.1 Ω || 0.22 Ω) above the cap junction, or 0.468 Ohms total from the Source to the speaker output. It looks funny, but sounds very nice.
I set R2 to a single value of 0.40 Ohms, 1%.
That helps bring up the bias current to a stable value in a more timely fashion. I also like the (now discontinued) FQH44N10 Mosfets. They happen to like higher voltage and bias current. I have taken advantage of this. Power rails are +/– 26.5V and bias is 1.95A, as recently re-adjusted and confirmed.
The next part may muddy the waters more than some builders want:
The source resistors in the output stage may be split into two values – one above the connection with the 1000 uF capacitor and one below. This possibility is discussed in Nelson's original article on the F6, back when it was still using the mostly unobtainable SemiSouth devices.
I have set R1 to a sum of 0.40 Ohms, 1% below the cap junction + (0.1 Ω || 0.22 Ω) above the cap junction, or 0.468 Ohms total from the Source to the speaker output. It looks funny, but sounds very nice.
I set R2 to a single value of 0.40 Ohms, 1%.