• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

GB "long and skinny" FirstWatt J2 clone PCBs

Jump to Latest
#181
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
 
#182
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?🙂
 
#185
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
 
#186
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
___________
 
#188
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
 
#189
vasillis said:
View attachment 789223


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

BR
Vasilis
Click to expand...

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.
 
#196
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.
 
#199
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?
 
You must log in or register to reply here.
Top Bottom