hi guys, I'm making the F5 Nelson but I have a serious problem in the setup phase. The R11 R12 resistors become very hot (close to smoke). I did not understand if the trimmers P1 and P2 must be zero Ohm or 5k to have the lowest possible bias. I replaced ZTX transistor with BC, do I need to change the value of any component?
I am attaching the diagram and the PCB that I designed, can someone tell me where I was wrong? Transistor or FET placement?
I'm very confuse ...😕
thank you very much!!!!
I am attaching the diagram and the PCB that I designed, can someone tell me where I was wrong? Transistor or FET placement?
I'm very confuse ...😕
thank you very much!!!!
Attachments
You have the J-fets (J74 and K 170) separate.
Usual design is for them to be tied together for thermal stability.
Pots should be at Zero to start (Measured, not guess work.)
A bulb limiter should be used for first start up.
Usual design is for them to be tied together for thermal stability.
Pots should be at Zero to start (Measured, not guess work.)
A bulb limiter should be used for first start up.
The BC transistors have a different pinout than ZTX, if you adjusted the pcb for that there will be no problem.
You want minimum resistance for least bias. R4 and R15 are in parallel with the pots, measure across them and set for minimum ohms.
Thermal tracking of Jfet is nice, but not necessary.
You want minimum resistance for least bias. R4 and R15 are in parallel with the pots, measure across them and set for minimum ohms.
Thermal tracking of Jfet is nice, but not necessary.
I know, this is only a temporary solution to make the first calibrations in comfort. The case will be metal and also open in under side ...
With this temporary solution the heat sinks reach 50 ° C after 2 hours of operation. And now, I can move everything into the definitive case.
With this temporary solution the heat sinks reach 50 ° C after 2 hours of operation. And now, I can move everything into the definitive case.
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