bugg wrote:Ahh yes, you are correct. It would have been C11 on your PCB.
Gotcha, so did your unit have a cap there? Only Q2 had a bypass cap in my friend's unit.
bugg wrote:Ahh yes, you are correct. It would have been C11 on your PCB.
bugg wrote:Yep, there was a source bypass cap on the second and third JFET stages.
bugg wrote:The trimpots are also set up slightly differently. Yours uses 50K trims with a 10K fixed resistor, mine has 100K trims with no fixed resistor.
bugg wrote:Your cap values are correct, except C8 is 22nF and C5 is 10uF. (The second source bypass cap is also 10uF)
bugg wrote:The FETs in mine were marked 62P, which is still a J201.
If I get a chance I'll measure their specs with my DCA75, but not sure if I'll have the time to crack it back open.
FlyingWild wrote:Here is another photo of the PCB all be it a little fuzzy
https://i.ibb.co/W6TpN7S/IMG-1970.jpg
It looks likes C6 and C11 are not populated just like the version Atalas traced, what effect will adding or subtracting the bypass cap C11 have, a hazy recollection when I built a tube amp a while back was that it increased gain and bass on that tube. But that was on the cathode of a valve, not sure how that relates to a FET.
Manfred wrote:Did you measure C5 and C10?
I estimated the size of the capacitors and therefore I would say that the values of they are greater than 10uF.
atalas wrote:Manfred wrote:Did you measure C5 and C10?
I estimated the size of the capacitors and therefore I would say that the values of they are greater than 10uF.
Yes, they were measured out of circuit by Bugg at 10uF.
brownwhopping wrote:How can I learn by reading threads an making circuits, when some day I can see a lawsuit or somebody beat me in the face for that?
Manfred wrote:atalas wrote:Manfred wrote:Did you measure C5 and C10?
I estimated the size of the capacitors and therefore I would say that the values of they are greater than 10uF.
Yes, they were measured out of circuit by Bugg at 10uF.
Hi Atalas, hi Bug
I thank you for your measurements and tracings, I appreciated it a lot.
I personally would use the Wambler Plexi Drive output circuity for a better treble control
Nocentelli wrote:Interesting - Wampler stated that the desired JFETs for the Plexidrive were ones that would bias to half supply with a 15k drain resistor. He claimed to have bought a shit-tonne of through-hole J201s, and sorted through to find ones that fit that spec: He claimed that others that biased to half-supply but required a much larger or smaller drain resistor value did not sound the same.
On this schem, Benson uses trimmers, has the drains at around 4.5v and drain resistance is close to 15k.
FlyingWild wrote:I've got some MMBFJ201 on order, but don't relish the idea of sorting through them to find a matched trio!
brownwhopping wrote:How can I learn by reading threads an making circuits, when some day I can see a lawsuit or somebody beat me in the face for that?
FlyingWild wrote:Any chance SMD FETs are more consistent than their through hole ancestors?
I've got some MMBFJ201 on order, but don't relish the idea of sorting through them to find a matched trio! Wouldn't be so bad if they could be tested as easily at the through hole variety.
Thanks for the link to the Fetzer Value page.
chasbenson wrote:May as well do it right.
knottypine wrote:Could I use 2N5457 in lieu of J201?
knottypine wrote:How about BS170 MOSfet?
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