F4 power amplifier

[Cambe]

Hello,
Who stocks the 2SK170/2SJ74 Semi's?
Cambe

 

[flg]

B & D Enterprises

http://www.bdent.com/

 

[Cambe]

Thank you, Flq. Now what type to use BL, GR or V ?
Cambe

 

[carpenter]

I see that Ampslab.com has both types for a buck apiece if your purchase in twenty dollar lots--forty bucks for twenty 2SK170 and twenty 2SJ74. I might have to check into this baby!

 

[marginwalker]

I bought some from Shuro.de: check 2sk170 item no. 851706 (0,60e) and 2sj74 851707 (1,10e). BL version is ok.

 

[flg]

Thank you, Flq. Now what type to use BL, GR or V ?
Cambe

I believe that question has been answered a few pages back... One of the higher Idss versions

 

[carpenter]

Perhaps this question's been asked before: can the Fairchild 9240 fet be substituted for the IRFP9240. Fairchild's fets are substantially less money!

I have plenty of IRFP240 fets for the other half of the output (no need to purchase more); I just wondered if the Fairchild fet would mate to the IRF fet.

John

 

[Zen Mod]

Perhaps this question's been asked before: can the Fairchild 9240 fet be substituted for the IRFP9240. Fairchild's fets are substantially less money!

I have plenty of IRFP240 fets for the other half of the output (no need to purchase more); I just wondered if the Fairchild fet would mate to the IRF fet.

John

just put 'em on test bench and match 'em ;

they don't know other's side name

 

[carpenter]

Thanks, Choky.

 

[niner]

C1 and C2

Got a question on C1 and C2: what's the max. voltage across them? I have some good capacitors, but they are lower voltage spec parts.

Thanks!

 

[Babowana]

Re: C1 and C2

Got a question on C1 and C2: what's the max. voltage across them? I have some good capacitors, but they are lower voltage spec parts.

We would need 5Vdc for the bias of the output mosfets.
On top of it, we would need to add 2Vrms input signal.
So, the maximum voltage across C1 or C2 would be about 11V
when the amp is operating as designed.

But, my preference is always the voltage rating of as big as the
rail voltage--just in case . . .

 

[niner]

Good advice! thanks. It's always better to be safe.

 

[protos]

I am sorry if this has been covered before but how can one use another circuit instead of the tl431 type to balance the output fets?

 

[Zen Mod]

I am sorry if this has been covered before but how can one use another circuit instead of the tl431 type to balance the output fets?

why?
if availability is reason - you can find them in every broken PC MoBo and PS

 

[protos]

Yes availability was my main concern.We have a lot of good things here in Rio but access to electronic parts is lacking.I will have a better look around but I was wondering if there was a simple way around it.We just need a constant / adjustable bias voltage right?

 

[Zen Mod]

Yes availability was my main concern.We have a lot of good things here in Rio but access to electronic parts is lacking.I will have a better look around but I was wondering if there was a simple way around it.We just need a constant / adjustable bias voltage right?

I'm pretty sure that you can find broken PC ....

 

[carpenter]

I have scads of IRF9630 and 630 transistors. They have about half the wattage capacity of the 240 series, but do handle 200 volts.

They have lower transconductance, but since this is a unity gain amp, the lower transconductance probably wouldn't matter too much...

What do you guys think? Is this transistor capable of operating as the power component of the F4?

John

 

[jleaman]

Does any one have some suggestions for first power up of the F4, i mean after populating the boards wiring every thing up and double checking every thing, what should be done ? What should the pots be set at ?
Hints - Help ?

 

[jacco vermeulen]

P1 set to Maximum , P2 in the centre position (~ R5 value)

The reference voltage for a TL431 is 2.5 Volts.
With P1 set at 5K there's roughly 6 Volts across the gates of the OP T's, at the zero setting 8 Volts.

 

[jleaman]

P1 set to Maximum , P2 in the centre position (~ R5 value)

The reference voltage for a TL431 is 2.5 Volts.
With P1 set at 5K there's roughly 6 Volts across the gates of the OP T's, at the zero setting 8 Volts.

Cool, i just don't want to blow this beast up, i just spend a good deal of money and time

Should a variac be used to power it up ?

You said P2 set to center position, ( ~R5 value ) does that mane set it to the value of R5 ?

Should i turn it on let it sit for a bit to warm up then set P2 to get 2.5V on TL431 ?

Sorry for the questions, with the alephs you just drop in a resistor an go

Jase