SemiSouth power Jfets .......... FW J2

[Tea-Bag]

Well, Good Morning guys.I swapped some of the power resistors to Sp300's standards.So ~ .33, .66, .33 - using 1R/.5r 2R/1R, 1R/.5rBias sets around .562v across Upper and Lower, Middle set at 1.1, problem is offset is now -.640v, and wants to go in the direction of down, so I have no room on R12,25 (at min), so it looks like I got to lower R26 (390), R35 (220).Should I start by going half value on each?Other problem is CNY17 in both channels is 1.0v, so this seems to be another problem. Previous measurements were at 1.3v, no problem. So looks like I need to change something here. I assume R28 (200R) needs to be lowered or raised. So just putting this out here looking for encouraging ideas. I assume R28 would be better at 150R.Tea

[sp300b]

Well, Good Morning guys.I swapped some of the power resistors to Sp300's standards.So ~ .33, .66, .33 - using 1R/.5r 2R/1R, 1R/.5rBias sets around .562v across Upper and Lower, Middle set at 1.1, problem is offset is now -.640v, and wants to go in the direction of down, so I have no room on R12,25 (at min), so it looks like I got to lower R26 (390), R35 (220).Should I start by going half value on each?Other problem is CNY17 in both channels is 1.0v, so this seems to be another problem. Previous measurements were at 1.3v, no problem. So looks like I need to change something here. I assume R28 (200R) needs to be lowered or raised. So just putting this out here looking for encouraging ideas. I assume R28 would be better at 150R.Tea

Hi Tea - Check posts 801, 802, 803.I think You have to increase R35 to 300 Ohm approximately and try then what is going on.Once You will be able to set offset with R12, R25 properly, CNY 17 will be OK.Reminder hereR28 could go down, but I think it will be not necessary if You change R35 (increase).Please, try and report.

[Zen Mod]

@ Teanegative bias means that lower SS is more open than upper SSif you can't in same time to increase bias and null offset - with trimpot R25 , increase R26 to 470Rleave R28 as is - you need minimal voltage for led operation , and that resistor is set for that - minimal needed voltage

[sp300b]

@ Zen - Now I'm confused... what Tea has to do:1) To increase only R352) To increase only R263) To increase bothWhich one is correct ?

[Zen Mod]

don't try to confuse me - thats pretty easy these days

if offset is negative - that means you need to more open upper SS

so - scenario is :

if - with R25 on max and R12 on min offset is negative - then increase R26 - to 470 or 510 ohms

[sp300b]

Tea disappeared - we confuse him completely

[Zen Mod]

naah - he's probably sleeping now

[Tea-Bag]

I am not sleeping! Working on this stuff like a good diy soldier.I tried R26 at 470R, brought down to -.500mv, then 680R, no down to four.So, try 500R or 1K pot for R25, or lower R35 to 100R?CNY pin 1 to 2 of DVM is 1.1vIt's like ZM says, R25 on max, R12 on min. Now Bias is higher, .640mv.

[sp300b]

I am not sleeping! Working on this stuff like a good diy soldier.I tried R26 at 470R, brought down to -.500mv, then 680R, no down to four.So, try 500R or 1K pot for R25, or lower R35 to 100R?CNY pin 1 to 2 of DVM is 1.1vIt's like ZM says, R25 on max, R12 on min. Now Bias is higher, .640mv.

Play twist with (try to adjust offset with him) R25 - Could You make offset 0V ?

[Tea-Bag]

Play twist with (try to adjust offset with him) R25 - Could You make offset 0V ?

No, it only went more negative on offset.

[sp300b]

No, it only went more negative on offset.

I would try 300 Ohm instead of 220 Ohm on R35

[Zen Mod]

set R25 to minimum - before increasing R26then go up turning R25what's , on earth , value for R35 at your pcbs ?

[generg]

no he is working hard.......... Last Active: 13 minutes agoCurrently:Viewing Topic: SemiSouth power Jfets

[Zen Mod]

I would try 300 Ohm instead of 220 Ohm on R35

that way - he'll even more open lower SS and offset will go neg. even more

[generg]

hear the laughter that no one can hear..............

[Zen Mod]

hear the laughter that no one can hear..............

[Tea-Bag]

set R25 to minimum - before increasing R26then go up turning R25what's , on earth , value for R35 at your pcbs ?

I lowered R25 pot, to 0, offset is -.760, turning higher lowers it down a bit to ~.5 to ~.4v.I checked R35, it is 220R.Before swap out of power resistors, both pots were near minimum.

[Zen Mod]

so ..... again :set R12 to minimumleave R35 as isif setting R25 to max can't bring you from negative offset -to 0 offset , then :turn back R25 to zero , increase value of R26 for max 220R ( from 390 to ,say, 610-620 (whatever you have in drawer) ) ;turn R25 up , to have 0 offsetset both Iq and offset - fiddling iteratively with R12 and R25Tea - these are simple thingsif you can't do it easily on Sunday afternoon - leave it for tomorrow

[generg]

sorry Zen Mod, I was amused by the communication structure between you, sp300b and tea-bag , it was a sort of comedy......

[generg]

we will find the holy grail......

[Zen Mod]

sorry Zen Mod, I was amused by the communication structure between you, sp300b and tea-bag , it was a sort of comedy......

we will find the holy grail......

now - it's my turn to ROFLMAO ........(even if today's communication isn't communication at all ........ you can't say who - amongst 3 of us - is more fucked in head today )

[Magura]

structure

:rofl:Magura