I must say that my experience with the SS F6 has been very rewarding.
I am looking for an opportunity to put a MosFET in my system.
That being said - the best amp in my system is buzzforb's "symmetric" Funny F6 using Onetics transformers and SS.) To my ears and with my speakers (driving midrange PHL 1130s) it gives the widest and deepest soundstage with nice articulation and placement of instruments. My comparison pool is ZenLite, Aleph 30, F3 (Nelson assembled),BA3B/crippled F4, F4 with Jensen interstage, and SS F6.
This is a fabulous thread and always, Nelson thanks for your gift(s) to the diy world.
Best to all experiments
Bob
I am looking for an opportunity to put a MosFET in my system.
That being said - the best amp in my system is buzzforb's "symmetric" Funny F6 using Onetics transformers and SS.) To my ears and with my speakers (driving midrange PHL 1130s) it gives the widest and deepest soundstage with nice articulation and placement of instruments. My comparison pool is ZenLite, Aleph 30, F3 (Nelson assembled),BA3B/crippled F4, F4 with Jensen interstage, and SS F6.
This is a fabulous thread and always, Nelson thanks for your gift(s) to the diy world.
Best to all experiments
Bob
Okay, having a few years ago built a chipamp with tantalum resistors and most recently having finished and being very impressed with a Shigaclone transport, I'm taking the plunge into building an F6, inspired by a few items...I'm partial to transformers owing to having used and loved the LA2a, Manley Varimu and EQP1A clone, and other fine recording gear; having seen some recpit mastering engineers with PASS amps; having seen Nelson's "The Quiet Earth" poster in one of Zen Mod's posts; and having owned a Nakamichi PA-7...I'm an Air Motion Transformer fan and the large ADAM monitors (S4C passive) I used with the PA-7 ended a bit slim in the mids and a touch crystalline in the highs, so I'm guessing that the F5, as described on this forum, would be more like the PA-7 in tonality than the F6...for those particular drivers.
My great appreciation to Nelson and to all who support such builds.
I've today received my matched 125 Semisouths from Semisouthfan, thank you! right as I note on the preceding page people discussing preferring IRFPs...I've been over the first 307 pages of this thread and much in the 500s, searching out specifics. I'll take it that I'm fine with a power supply of the F5 type as well as heat sinks better than .28. Heatsinkusa have a type which in the comments, if they can be trusted, suggest that a 15" length would be about .226 for about $33 each:
4.600" Wide Extruded Aluminum Heatsink - HeatsinkUSA, LLC Store
Am I in error or correct? I have good ears and a deep passion for music and sound but am very light on the left brain stuff...very excited about this build!
My great appreciation to Nelson and to all who support such builds.
I've today received my matched 125 Semisouths from Semisouthfan, thank you! right as I note on the preceding page people discussing preferring IRFPs...I've been over the first 307 pages of this thread and much in the 500s, searching out specifics. I'll take it that I'm fine with a power supply of the F5 type as well as heat sinks better than .28. Heatsinkusa have a type which in the comments, if they can be trusted, suggest that a 15" length would be about .226 for about $33 each:
4.600" Wide Extruded Aluminum Heatsink - HeatsinkUSA, LLC Store
Am I in error or correct? I have good ears and a deep passion for music and sound but am very light on the left brain stuff...very excited about this build!
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Go with the 10.08 profile and turn the fins vertically. 6-7" tall is good and you will need 2 per side. You can try a single per side, but I would go to 8-10" for that. Don't worry, matched SS fest from SS fan are the way to go. I preferred the Onetics, then the Cinemag, and then the Jensens. Shows you how taste differ. I love music but can't hear a thing. Make a commitment to build just this one amp or you are in trouble. 
Go with the 10.08 profile and turn the fins vertically. 6-7" tall is good and you will need 2 per side. You can try a single per side, but I would go to 8-10" for that. Don't worry, matched SS fest from SS fan are the way to go. I preferred the Onetics, then the Cinemag, and then the Jensens. Shows you how taste differ. I love music but can't hear a thing. Make a commitment to build just this one amp or you are in trouble.
I'm going to stick with the SemiSouths; should have put a smiley emoticon there...it was a pleasure dealing with SemiSouthFan...and yes, I've long since learned that =the= most important thing in DIY is making firm decisions about what =not= to build!
I have to go horizontal / slimline like the case shown in the 6moons article; I have significant space restrictions at the moment...cheers everyone.
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Help needed… refering to my biasing problem… I’ve done some measuring but lack the knowledge, so could you wise guys do some analysing, please…?
The problem again:
I made some cap mods and then couldn’t get the left channel to bias up enough. Also I should note that I accidentally shorted the Gate and Drain leads of the left channel positive jfet – only for a millisecond with the DMM probe, but it did give a spark. Bad..?
Mind you though that the amp does work and there's nothing obviously wrong when listening.
What I came up with with the measuring:
Bias (measured across 0.1 ohm degeneration resistors and via power input)
- Right channel 156 mV both jfets
- Left channel 136 mV both jfets (does not bias higher)
Offset
- offset for both channels can be set to about 10mA and under
Voltage over the LEDs
- from 2.98 to 3.1 volts.
Gate leakage:
- right channel: 1.53 mV and 0.95mV
- left channel: 7.25 mV & 0.28 mV (!)
Dismounted the bias pot and jfets (left channel):
- pot is fine – still 5K
- resistors around trimpot are fine also
- tried to measure the jfet’s with same jig as 2SK170 but am not getting proper results I’m afraid.
• Stated Vgs when new: 1.50Vgs & 1.48Vgs
• With the jig both measure current of about 1.3 amps and quickly plunges from that (also heats up quickly so not held long in the jig).
• same jig but voltage measured between probes 7.58Vdc and 7.99Vdc (not sure this has any meaning though)
The questions:
So what you guys say? Is the left channel (0.28 mV gate leakage) jfet damaged or is there still something else to take into account?
I can of course put the extra LEDs in to bias higher (as Generg suggested), but since the amp did before bias up to 1.55 amps, would that just be a bandage in stead of a fix? - or would that actually fix the gate leakage difference issue?
Thanks!
The problem again:
I made some cap mods and then couldn’t get the left channel to bias up enough. Also I should note that I accidentally shorted the Gate and Drain leads of the left channel positive jfet – only for a millisecond with the DMM probe, but it did give a spark. Bad..?
Mind you though that the amp does work and there's nothing obviously wrong when listening.What I came up with with the measuring:
Bias (measured across 0.1 ohm degeneration resistors and via power input)
- Right channel 156 mV both jfets
- Left channel 136 mV both jfets (does not bias higher)
Offset
- offset for both channels can be set to about 10mA and under
Voltage over the LEDs
- from 2.98 to 3.1 volts.
Gate leakage:
- right channel: 1.53 mV and 0.95mV
- left channel: 7.25 mV & 0.28 mV (!)
Dismounted the bias pot and jfets (left channel):
- pot is fine – still 5K
- resistors around trimpot are fine also
- tried to measure the jfet’s with same jig as 2SK170 but am not getting proper results I’m afraid.
• Stated Vgs when new: 1.50Vgs & 1.48Vgs
• With the jig both measure current of about 1.3 amps and quickly plunges from that (also heats up quickly so not held long in the jig).
• same jig but voltage measured between probes 7.58Vdc and 7.99Vdc (not sure this has any meaning though)
The questions:
So what you guys say? Is the left channel (0.28 mV gate leakage) jfet damaged or is there still something else to take into account?
I can of course put the extra LEDs in to bias higher (as Generg suggested), but since the amp did before bias up to 1.55 amps, would that just be a bandage in stead of a fix? - or would that actually fix the gate leakage difference issue?
Thanks!
Attachments
You should still go with vertical fins. It is a significant increase in dissipation, from what I have read.
I remember that the Aleph 5 is a vertical configuration, but this page says that horizontal is much more efficient?
http://www.diyaudio.com/forums/pass-labs/223532-f6-heatsink-calculations.html
D'oh. Yep, even my PA-7 shows this. I got stuck on the F6 unit in the 6moons article with the horizontal fins. 6moons audio reviews: FirstWatt F6
Read other Firstwatt articles and look closer at the fins. Horizontal is not the full story.