GB "long and skinny" FirstWatt J2 clone PCBs

[RustySanwa]

Malvin 1 set
pfisla 2 sets
Myint67 1set
twitchie 1 set
gig 1 set
flamethrower1 1 set
necplusultra 1 set
vvs07 2 sets
Dr.Strangelove3 1 set
WBS ???
malisz ???
dieter12 2 sets
Fabian85 ???
Scott Stansbury - 1 set
pistollero - 2 set
nashbap 1set
mlwebb 1 set
Ibuell 1 set
Gnub 2 sets
Spades 1 set
RustySanwa 2 sets

 

[gary s]

Thanks or the reply Jeff, forgot no bias pots to tweak, so at a nominal +/- DC supply of 24V, that puts the power dissipation in each device at about 32 watts or so - comfortable.

Can I ask , what device have you currently got in the CSS position and also have you measured the heat sink/device temps for the chassis you are using?

 

[JeffYoung]

Hi Gary,

SJEP in the CCS. For temps, see here: Long skinny builders thread

Cheers,
Jeff.

 

[gary s]

Thanks Jeff, now I remember you posting that detail in the other thread.

Any changes to source resistor values, or any other tweaks from your original schematic?

 

[Rodeodave]

Malvin 1 set
pfisla 2 sets
Myint67 1set
twitchie 1 set
gig 1 set
flamethrower1 1 set
necplusultra 1 set
vvs07 2 sets
Dr.Strangelove3 1 set
WBS ???
malisz ???
dieter12 2 sets
Fabian85 ???
Scott Stansbury - 1 set
pistollero - 2 set
nashbap 1set
mlwebb 1 set
Ibuell 1 set
Gnub 2 sets
Spades 1 set
RustySanwa 2 sets
Rodeodave 1 set

 

[KevinHeem]

Malvin 1 set
pfisla 2 sets
Myint67 1set
twitchie 1 set
gig 1 set
flamethrower1 1 set
necplusultra 1 set
vvs07 2 sets
Dr.Strangelove3 1 set
WBS ???
malisz ???
dieter12 2 sets
Fabian85 ???
Scott Stansbury - 1 set
pistollero - 2 set
nashbap 1set
mlwebb 1 set
Ibuell 1 set
Gnub 2 sets
Spades 1 set
RustySanwa 2 sets
Rodeodave 1 set
kevinheem 1 set
___________

 

[vasillis]

View attachment 2sj109bl.pdf


Hi folks. I wonder if them are genuine or not.

BR
Vasilis

 

[soundslave]

Malvin 1 set
pfisla 2 sets
Myint67 1set
twitchie 1 set
gig 1 set
flamethrower1 1 set
necplusultra 1 set
vvs07 2 sets
Dr.Strangelove3 1 set
WBS ???
malisz ???
dieter12 2 sets
Fabian85 ???
Scott Stansbury - 1 set
pistollero - 2 set
nashbap 1set
mlwebb 1 set
Ibuell 1 set
Gnub 2 sets
Spades 1 set
RustySanwa 2 sets
Rodeodave 1 set
kevinheem 1 set
Soundslave 1set

 

[JeffYoung]

View attachment 789223


Hi folks. I wonder if them are genuine or not.

BR
Vasilis

Hi Vasilis,

The lettering doesn't look quite like mine (the letters have too much space between them). That doesn't mean Toshiba didn't change the lettering over time, but I'd be suspicious.

Do you have them in hand? Do they measure as JFETs? Most fakes I've heard about have been BJTs labelled as a 2SJ109, which should be easy enough to test. There's a bunch of info here: GB: for 2SK389 and 2SJ109.

Cheers,
Jeff.

 

[JeffYoung]

Did anyone buy 2SJ109s from tommygun_nz on eBay? How did they turn out?

 

[astromo]

Did anyone buy 2SJ109s from tommygun_nz on eBay? How did they turn out?

Yes.

Refer FirstWatt J2 Post #1453.

Look ok?

Note that I haven't put them to use yet. So, yet to be road tested.

 

[vasillis]

Thanks for reply Jeff.
i have them in hand soon.i test them and i post the result.

BR
Vasilis

 

[blackdod]

Yes.

Refer FirstWatt J2 Post #1453.

Look ok?

Note that I haven't put them to use yet. So, yet to be road tested.

Interesting. I don't know if I should take a chance

 

[JeffYoung]

@astromo, yep, they look OK to me.

@blackdod, based on astromo's tests I think they're worth a gamble. But everyone's level of risk tolerance is different....

@Vasilis, if they do turn out good, does the source have more of them?

 

[Dr_Strangelove]

I looked in my stash of parts. But I only seem to have V grade 2sj109...
Can I use a single V grade instead of BL grade?
What are optimum Idss values of 2sj109 and 2sk170?

 

[JeffYoung]

As far as I understand it the only requirement for the 2SJ109s is that they're comfortably over the LTP current. The more over they are the less linear the operating point is, but I've been lead to believe this isn't the end of the world. If this is correct then V grade will work fine, but isn't strictly optimal.

I calculated the LTP current (ie: the two 2SK170s added up) to be optimal at 8.5mA, but again, the sweet spot is pretty shallow so I'm not sure it matters much. This means you want GR parts. See Long skinny builders thread.

Sadly I didn't get any feedback on my analysis, so I don't really know if it's correct or not....

The other thing I'm curious about (but don't know) is the relative effects of hitting the LTP current sweet spot vs. the distortion reduction of using two CCS JFETs. In other words, is a single 8.5mA 2SK170 better or worse than a pair of 5mA 2SK170s?

Cheers,
Jeff.

 

[Dr_Strangelove]

Thanks Jeff!

 

[JeffYoung]

The boards do indeed make music.

For a more detailed report see: Long skinny builders thread.

Any volunteers to organize a second run?

 

[gary s]

Hi Jeff,

Good to hear your J2 is working and playing music. Also read your report in the other thread with regards comparison to your F5 build - especially interesting seeing these 2 amps use totally different output devices as well. I wonder if the sonic character on the J2 will change after it has been "burned in" after some hours use?

A question on the J2 for you - did you keep a record or measure the ID in the long tailed input pair and the individual Idss figures on both the 2SK170 GR and 2SJ109BL fets? Is it close to the 8.5mA you worked out in your modelling?

 

[Dennis Hui]

Any volunteers to organize a second run?

If it's just ordering boards and sending them out (and no cutting MDF )
then I can volunteer.

Dennis