@Zen Mod,
Thank you for pointing this out.
I reread the F6 article on Firstwatt website. Nelson clearly states that F6 was build with SemiSouth SJEP 120100.
As I'm going to upgrade my F6 to Mk II version soon (I will add second PSU to make it a dual mono), maybe I could test it with some other output devises. Can you suggest any other alternatives with reasonable prices and availability (FET rolling!)?
Best / Smelay
Thank you for pointing this out.
I reread the F6 article on Firstwatt website. Nelson clearly states that F6 was build with SemiSouth SJEP 120100.
As I'm going to upgrade my F6 to Mk II version soon (I will add second PSU to make it a dual mono), maybe I could test it with some other output devises. Can you suggest any other alternatives with reasonable prices and availability (FET rolling!)?
Best / Smelay
Is this the IRFP150 that I should order if I wanted to replace the 240's with the 150's? Just need four of these right?
https://www.mouser.com/ProductDetail/onsemi-Fairchild/IRFP150A?qs=FOlmdCx%2BAA1DLtAv0RJScw==
Thanks!
https://www.mouser.com/ProductDetail/onsemi-Fairchild/IRFP150A?qs=FOlmdCx%2BAA1DLtAv0RJScw==
Thanks!
What is the brand of the source resistors on the F6 DIY store kit? I did some searching around but couldn't find it. They are metal oxide correct?
1) I'd like to buy the Store F6 board - just pcb's (https://diyaudiostore.com/pages/project/f-6 ) But there is none.
2) Handy nice designed diamond print by C Holmberg; my cart at PcbWay site says: 5 boards only for $60.-. What am I doing it wrong??
I do have the Jensen transformers so need only a PCB. Just to replace my test outfit:
2) Handy nice designed diamond print by C Holmberg; my cart at PcbWay site says: 5 boards only for $60.-. What am I doing it wrong??
I do have the Jensen transformers so need only a PCB. Just to replace my test outfit:
The original F6 was with now obsolete power jFETs. Is the UJ3N065080K3S SIC jFET useable? I have not seen a reference to this yet.
However, one might need mighty tricks to handle it: because the nice behaviour is only there at low Vds --> a cascode os needed?
https://www.diyaudio.com/community/threads/power-jfets-in-production.331156/post-6311574
- But then, one could also use the LU1014 . . for a soundwise very reliable result (apart from bias shift), if designing a cascode. . .
However, one might need mighty tricks to handle it: because the nice behaviour is only there at low Vds --> a cascode os needed?
https://www.diyaudio.com/community/threads/power-jfets-in-production.331156/post-6311574
- But then, one could also use the LU1014 . . for a soundwise very reliable result (apart from bias shift), if designing a cascode. . .
The production FW F6 uses IRFP240, not Semisouth devices - see page 9 of the F6 owners manual.
There are a few SemiSouth R100 built F6s running around but only Papa Nelson can tell you how many of those there are.
This last item makes for an interesting story because the F6 started out as a very nice amplifier using the SemiSouth R100 enhancement-mode power Jfets. While SemiSouth is no more, I have an adequate stock to support production, and I originally thought to use them for this. However I was in no hurry to get it out, and so had the time to play around with other gain devices, including the R085 depletion-mode Jfets and the SIT-1 transistors.
It was surprising that the R085 and SIT transistors did not perform as well since they had done a little bit better job than the R100's in single-ended circuits. By this I mean that people did not like the sound as much – the specs were ok.
The primary difference is that the R100 has a higher Drain impedance, that is to say that it behaves more like a voltage controlled current source, where the other parts behave a bit more like voltage controlled resistors. In tube vernacular you would say that the R100 is “Pentode-like” and the others were more “Triode-like”.
The single-ended J2 and SIT-1 amplifiers are fine examples where the best performance is obtained by low impedance Drain types of transistors, and in both cases they are fed current by (relatively) distortion-free current sources – in the case of the SIT-1 a big power resistor. Meanwhile, I have examples of pushpull circuits where the “Pentode-like” devices are preferred.
This of course led me back toward a device more like a Pentode than the R100, of which the IRFP240 is a fine example. Putting that device in this topology resulted in better sound, so it stayed.
There are a few SemiSouth R100 built F6s running around but only Papa Nelson can tell you how many of those there are.
This last item makes for an interesting story because the F6 started out as a very nice amplifier using the SemiSouth R100 enhancement-mode power Jfets. While SemiSouth is no more, I have an adequate stock to support production, and I originally thought to use them for this. However I was in no hurry to get it out, and so had the time to play around with other gain devices, including the R085 depletion-mode Jfets and the SIT-1 transistors.
It was surprising that the R085 and SIT transistors did not perform as well since they had done a little bit better job than the R100's in single-ended circuits. By this I mean that people did not like the sound as much – the specs were ok.
The primary difference is that the R100 has a higher Drain impedance, that is to say that it behaves more like a voltage controlled current source, where the other parts behave a bit more like voltage controlled resistors. In tube vernacular you would say that the R100 is “Pentode-like” and the others were more “Triode-like”.
The single-ended J2 and SIT-1 amplifiers are fine examples where the best performance is obtained by low impedance Drain types of transistors, and in both cases they are fed current by (relatively) distortion-free current sources – in the case of the SIT-1 a big power resistor. Meanwhile, I have examples of pushpull circuits where the “Pentode-like” devices are preferred.
This of course led me back toward a device more like a Pentode than the R100, of which the IRFP240 is a fine example. Putting that device in this topology resulted in better sound, so it stayed.