F6 Illustrated Build Guide

[Georgeged]

6.2V. R7 ad R8 3K3

 

[2 picoDumbs]

First check voltage drop across Zener

If that looks correct the measure Voltage between Gate and Source of each mosfet

 

[Georgeged]

Voltage accross zenner:
Z1 - 5.93V
Z2 - 6.02V

Voltage between G and S of the mosfets:
Q1 - 2.72V
Q2 - 2.57V

 

[2 picoDumbs]

Then either you have some kind of weird issue with your trimpots or you haven't adjusted them correctly.
Try and get 3.8V to 4V gate to source as an intermediate first step, then remeasure everything

 

[Georgeged]

It was a trimpod. I made one full turn to one end and then to another and it start working! Bias and Offset are adjusted, now voltage between G and S is 4.46V on Q1 and 4.48v on Q2
Thank you for your help 2picoDumbs!

 

[2 picoDumbs]

Awesome.

Good job.

 

[tamra]

I found 2sk1530 for 5usd.
Do I need to change resistor value somewhere?
Size is bigger than Irpf240 so I have to tap again.

 

[tamra]

I tried to setting bias with 2sk1530.
But couldn't set bias current well and gate resistor get
too hot so I quit doing set the bias...

 

[2 picoDumbs]

I found 2sk1530 for 5usd.
Do I need to change resistor value somewhere?
Size is bigger than Irpf240 so I have to tap again.

I would use 0.22 Ohm source resistors.
No other changes are needed.

 

[2 picoDumbs]

I tried to setting bias with 2sk1530.
But couldn't set bias current well and gate resistor get
too hot so I quit doing set the bias...

2sk1530 needs far less voltage from gate to source compared with IRFP240.
If gate resistor is hot then likely the mosfet is oscillating.
Increase gate resistor to 100 Ohms.

 

[2 picoDumbs]

Size is bigger than Irpf240 so I have to tap again.

Shouldn't need to tap again. You just bend mosfet pins differently.

 

[tamra]

Thank you picoDumbs.
Because I only have limited time to treat my amplifier,
I swapped to Irfp240 again.
I might try with 0.22ohm later when I got more day off.
Now,I changed new Irpf240 from diyaudio store.
I used to use vishay Irfp240 but seems deferent.
Bias voltage doesn't raise more than 0.9v.
So now I need to add one more Led?

 

[2 picoDumbs]

Do you mean 0.9V across 0.47 source resistor?

 

[tamra]

Yes,R2 is 0.47 ohm.

 

[6L6]

0.9V (900mV) across 0.47ohm is 2.25A !!

That is more than 2x recommended bias.

Nelson Pass suggests bias of 0.5v across 0.47 ohm source resistor.

 

[2 picoDumbs]

1.91A not 2.25A

In either case is more than enough.

1.5A is a nice bias point.

 

[tamra]

Ohhh, I have been busy these days and had stupid mistake 1.5v and 1.5A...
I think I could use 2sk1530 then. I might check it in new year.
With Irfp240 F6 sound amazing. I might use F6 whole my life.
I changed source resistor and gate stopper with manganin resistors then bass have got tight and vocal sound realistic.
Still looking for isabellenhutte PBH 100ohm 3w.
Anyway thank you for my stupid questions.

 

[2 picoDumbs]

Yeah
I love F6 too.

 

[jameshillj]

Tamra, I don't the 100R 3W Isab/h resistors are available anymore but I'll send you a PM - not listed under the Powertron name either.

 

[tamra]

Thanks ��
I have been checking websites then found some are selling in Russia and Germany but they did not reply
Email.