Gyuri's Pass SONY VFET2 build.

[Gyuri]

At Q8 position I would like to use IRFP9140 parts.
Any comment?

 

[Zen Mod]

why not

 

[Gyuri]

Actually, it wasn't a question, which would like an answer.
After all, I built F4 amplifiers with IRFP9140 and IRFP9240.
So I know the answer.
Neither measurement nor hearing I can not know to distinguish them from each other.
I'm more interested in the value of resistors.

 

[Zen Mod]

practically 29V5 is same as 30V

you have your answer , post #39 , text part for 30V

 

[Gyuri]

Well, the chosen resistor value is 42.2Kohm for R15/R16.
Because I have these.

 

[Gyuri]

So where I'm with these?
All of the parts are in place, except VFETs.
Testing Part1, Part2, and Part3 was done.
Everything was O.K..
Frontends sucks about 55mA. 5.5mV/0.1Ohm.
Voltages are set.
Even at T18, (front end output) although it is a little bit funny.
If I blow some air on input JFETs, it can change more than 0.6V.

I give back that suspicious tranny, and get another one(s).
I have four of them now.
I think these are O.K..
They are sucks currents without load, as follows here:

1.
230VAC/50mA
220VAC/37mA
250VAC/128mA

2.
230VAC/90mA
220VAC/75mA
250VAC/163mA

3.
230VAC/54mA
220VAC/44mA
250VAC/130mA

4.
230VAC/64mA
220VAC/55mA
250VAC/114mA

Just as a reminder, that drek was sucks 5A at 242VAC.

 

[Gyuri]

VFET2

 

[Gyuri]

VFET2 BEAG

 

[Bones13]

Looks great! Good luck with powering it up.

 

[Gyuri]

Thanks!
You know, I wouldn't trust in my luck.
I'm a fearless BA builder, for sure.
However in this case I'm more careful.
Above I was whining about FE DC offset settings.
Everything was simple and straightforward, except this.

Papa wrote it:

"If it looks reasonably stable over a period of time, then we are ready for the final
assembly and tests."
and:
"Keep in
mind that this is a good time to get these values and a low DC offset right. It
becomes a little more complicated when the VFETs are installed and the
feedback loop starts working."

Voltages at R5-R6 and T16-T17 are O.K..
Randomly changing DC offset at T18 not O.K. for my opinion.
It changing more than 1V, if I blow some air on JFETs.
So VFETs remains in the box for a while.
I would like to know, other builders experienced a similar occurence?

 

[Gyuri]

You can say it, then you wacky one, do not blow it!

 

[Gyuri]

Forgot to say, a very slightest change at P3 or P4 results a couple volts change at T18.
Is this normal?
I'm using this 20 turns trimmer at P3-P4 position, I think it is not the crappiest one:
http://hu.mouser.com/ProductDetail/BI-Technologies-TT-Electronics/67WR500LF/?qs=sGAEpiMZZMvygUB3GLcD7jZSyzxDqivkG93jEX1vRMU%3d

 

[Gyuri]

At T14-T15 points I can measure about 14.5V instead of 13V.

 

[Gyuri]

On R34-R35 there are 2Vs.

 

[Gyuri]

Measured Idss of JFETs was 8.8mA.

 

[Gyuri]

It doesn't matter, I grounded input or not.

 

[Gyuri]

Am I the only one, who is fighting against a bouncing DC offset at T18?

 

[Zen Mod]

maybe I'll collect few cells tonight to grasp few things from schematic

 

[Gyuri]

In my opinion, the phenomenon is closely related to the temperature of JFETs.
Even heat radiated by my hands near JFETs, causes changing DC offset at T18.

 

[Gyuri]

I am also using ZTX450/ZTX550.