Is it wrong in F5 TURBO V3?

[lilinyi]

In the F5 TURBO V3 sch..R25=10K but the R26=47.5K,is it wrong?

[Itsmee]

R26 should be 10K

[flg]

As Itsmee says, and N.P, "In the example of cascode Q7, a voltage reference is set by resistors R25 and R27 between V+ and Ground so that the Jfets see about 1/3 of the rail voltage." In order for "them" to see 1/3 the rail voltage, yes, R26 would be about 10k!

[anilva]

Is this confirmed? I am about to fire up my V3...

[bobodioulasso]

Confirmed though use a bulb and don't fear anything.

[buzzforb]

It is a voltage divider as stated. It sets the voltagre at the base of the bjt, which sets the voltage that thecdrain of the input fet sees. Fire it up and let it burn.

[anilva]

I had soldered a 47.5K. Looks like I need to replace with a 10K.

[buzzforb]

this is a good example of how important it is to try to understand how the circuit actually works over just building it. If you are going for a one shot deal, I can understand just putting it together, but if you want to continue on in building different things, try to look beyond the values and into the circuit and understand why they are there and what it is that they do. I have often found deep satisfaction in finally understanding what others may consider trivial. For me it is another life/learning experience.

[AudioSan]

R25-R28 is not fixed. they can be adjusted for everyones need and and rail voltage.

[anilva]

Originally Posted by buzzforb

this is a good example of how important it is to try to understand how the circuit actually works over just building it. If you are going for a one shot deal, I can understand just putting it together, but if you want to continue on in building different things, try to look beyond the values and into the circuit and understand why they are there and what it is that they do. I have often found deep satisfaction in finally understanding what others may consider trivial. For me it is another life/learning experience.

There are people who understand the circuits and the role of each component very well and would like to experiment and then there are some like me who understand basically and superficially at a block level and cannot go beyond that, not for lack of application but due to certain limitations. For me lack of complete understanding does not prevent me from building. I hope these builds work and if it does not - seek help from forum members and see where it ends up. I would rather try and fail, than not build anything at all. Different strokes for different folks...