F5 power amplifier

[AndrewT]

you need high transconductance, medium voltage Vds, lowish noise, jFets of both N and P channel.

The input JFETs used are 2SK170 or 2SK370 for the N channel parts (Q1), and 2SJ74 or 2SJ108 for the P channel parts (Q2). In these cases the Idss selection code is BL, although V and GR types will also generally work fine. The primary thing about these particular parts is the transconductance figure of 20 mS – many of the potential substitutes are much lower at 4 to 10 mS.

The Pchannel are often the ones that are difficult to source.

Have you downloaded the PASS manual for the F5?

[sangram]

Yup, and I can't find any of those parts, either 74/370 or 108/170 I poked around here on DIYA trying to get an answer and I dug up this thread

Toshiba 2sk370 and 2sj108

But it didn't help any. I'm trying to scour the D-K pages looking for alternates. The voltage ratings are easily available but getting the gm and noise figures are proving quite a task.

[Diomedian]

Originally posted by sangram
I'm sorry if I missed this in the 180-page thread, but are there any reliable substitutes in the Digikey catalog for the input pair J108/K170?

I've ordered from:
www.amb.org
www.ampslab.com

and have heard good things about:
www.tech-diy.com

These are all based in the US though - contact them to see if they will ship to India. Alternately, I'm sure there are places in Europe that stock these parts - the shipping may be a bit more reasonable.

-j

[Renron]

I bought and recieved all my parts in short order from Jackinnj at Tech-Diy.com ....easy to do business with!

Thanks Jack!

Ron

[sangram]

Thanks a lot for the responses, and even to those who emailed me

I was hoping to save on shipping cost by using a single source for all my parts. I notice that Jack has complete partlists for the F5, so maybe that's the ticket. He does mention something about customs, so I'm assuming he ships international.

European suppliers may have slightly lower shipping, but the parts seem to be more expensive.

I noticed in the 6moons review that Nelson has used 5% Panasonic Metal oxide resistors from D-K. Would there be any downside to just using resistors available locally? The quality of resistors here isn't the best - values may be off tolerance, suspect materials may be used, and resistors may be significantly inductive. But much, much cheaper.

Or potentially, an upside to using 'premium' resistors in this design?

Thanks again!

[lalaina]

hi

many thanks to all your replies , very helpfull for me.

After some test, I have changed the 3 wires ( +, - , GND) between the capacitor of the power supply and the amplifier card to a torsaded computer lan CAT6 wire.

like this (one channel only for the test)



and this is the result of the trace , more stable than before



and this



at 20khz



and for the fun at 1Mhz



my power supply , CRC 40 000µf+(0,68/4) +100 000µf for each line



I think that I use a fake 9240 (local seller) , I will post the trace on the gate of the 240 and the 9240. I think that the 2940 that I use have too much capacitance between the gate and the source. I'v forget to save it during test.

Thanks to all

Lalaina

[Mooly]

It's looking pretty good overall.
Is this an atifact of the scope/image or is it HF oscillation.

[Mooly]

And this also.

[Mooly]

It's still all very good though

[lalaina]

Hi Molly,

I think that it is not an oscillation.

this is a digital scope, that is the problem with digital scope