Who would ever accuse you of copying anything? [joke...........don't move it to Texas this time!]
Right, Charlie?
BTW, Steve.......yesterday is over. [yet another joke]
Jocko
Right, Charlie?
BTW, Steve.......yesterday is over. [yet another joke]
Jocko
Charles Hansen said:
Sorry Charles, you've lost me.
At 10VDS the 2N6550 has a typical Ciss of 30pF. At 10VDS the 2SK389 has a typical Ciss of 25pF.
At 10VDS and an ID of 10mA, the 2N6550 has a typical gm of 40mS. At 10VDSS and an ID of 10mA, the 2SK389 appears to have a typical |Yfs| of a little over 30mS.
So what am I missing here? How does the 2N6550 have three times the input capacitance at 10VDS as the 2SK390 and why would it need three times the transconductance?
That's a nice little device. Not as sexy looking as the metal can devices, but... 🙂
Who's still producing it?
By the way, I've been thinking about doing this for the last 10 years, but have never actually built the thing. If we ever do, please don't accuse me of copying Nelson!
Ok. I won't accuse you of it then. I'll accuse you of it now. 😀
se
Jocko Homo said:
No it isn't. I'm spinning it up right now.
Yesterday, all my troubles seemed so far away
Now it looks as though they're here to stay
Oh, I believe in yesterday.
Suddenly, I'm not half the man I used to be,
There's a shadow hanging over me.
Oh, yesterday came suddenly.
Why she had to go I don't know she wouldn't say.
I said something wrong, now I long for yesterday.
Yesterday, love was such an easy game to play.
Now I need a place to hide away.
Oh, I believe in yesterday.
Why she had to go I don't know she wouldn't say.
I said something wrong, now I long for yesterday.
Yesterday, love was such an easy game to play.
Now I need a place to hide away.
Oh, I believe in yesterday.
Mm mm mm mm mm mm mm.
se
Do you (or anyone else) by any chance have datasheets for the 2SJ18 and 2SK60? They came from a TA-4650, which was blown, but some of them might be ok.janneman said:
janneman said:
The TA-7 is interesting in that regard, they use power JFETs
but not as gain devices.....
I suspect it worked very well nonetheless given the cascoding
of very fine bipolars.
😎
Steve Eddy said:
It's OK, Erno Borbely made the same mistake in his original article on MOSFET amps in the Audio Amateur 25 years ago or so.
Remember that Ciss = Cgd + Cgs. But also remember that Q = CV. In a follower Cgs doesn't matter because you don't have to charge it up -- the source is following the gate. So the thing that matters in a follower is Cgd. For some reason Cgd is also called Crss, which is plotted on the data sheets. That is what I was looking at.
One measure of merit for a FET follower is the ratio of transconductance to Crss. By this parameter, the Japanese part is quite a bit better than the American part.
As far as availability, the Japanese transistor numbering system works differently than the US system. In the 2Sxxxx system, the same die in different packages receives a different number (and it's usually not sequential). If a different manufacturer makes and equivalent part, it receives yet another part number. So when you specify a number such as 2SK170, the only manufacturer for this part is Toshiba, and it's in a TO-92 package.
There isn't enough demand for it here in the US for Toshiba America to import it. Instead it is brought in via various grey market sources. Try Dalbani or MCM for smaller quantities.
I tried to talk Digi-key into buying 3000 pieces of some of our favourite transistors, which is the minimum order. I even offered to buy all of the initial order, just to get them in the catalog.
They would not go for it. I tried...............
Jocko
They would not go for it. I tried...............
Jocko
Charles Hansen said:
Ah well. Guess I'm at least in fairly good company. 🙂
Ok, gotcha.
Not sure that's the case as the Crystalonics datasheet for the 2N6550 specs Ciss, Crss, and CGD, at 30, 17 and 20 respectively.
In any case though, whether Crss or CGD, in a common drain follower, won't that be effectively reduced by the transconductance of the device?
Yes. But for what I'm wanting to do, due to the 2SK170's maximum IDSS being five times lower than the 2N6550's typical IDSS, even though they're both 400mW devices, I'd have to use more than twice the number of 2SK170s as the 2N6550s. And in that context the 2SK170's advantage isn't much of an advantage if any.
Unless I'm overlooking something again.
Yeah, that part number didn't even come up on Toshiba's US website. I'd found a number of distributors selling it but wasn't sure if they were NOS devices or not.
Thanks, Charles.
se
Steve Eddy said:
I just look at the graphs. The graph on the InterFET parts shows Crss at about 18 pF at 10 volts.
Steve Eddy said:
No.
Assuming you are using a 20 volt rail, then running the devices at 10 mA will give 200 mW of dissipation. This 50% safety factor is about right. If you are cascoding them with something else you could run a higher standing current, but you still have to keep the Id max in mind.
Try this:
http://www.semicon.toshiba.co.jp/eng/prd/tr/index.html
Then click on small-signal FETs on the left-hand side.
Charles Hansen said:
Yeah. Not a significant difference between them. I was just pointing out that it doesn't seem that they're using Crss and CDS to mean exactly the same thing.
Ok. Guess this is one of those cases where negative feedback doesn't help.
Yeah. But I'm going to be using a 12 volt rail and about 1.25A quiescent. That gives 1.25/0.01, or 125 devices with a total capacitance of 750pF. I should be able to do the same with 50 2N6550s for a total capacitance of 900pF. Not such a huge difference.
Thanks, but I already have the datasheet. Got it from ampslab.com.
se
Steve Eddy said:
Run the transconductance numbers and tell me what you see.
Steve Eddy said:
I was pointing out the fact that the part is still in production.
Charles Hansen said:
But I'll still ultimately see 750 and 900 pF, yes?
Ah. Ok. After I read your first post I went to Toshiba Japan's website and found it still active.
se
Why not just use one FET and parallel it with a 10 ohm resistor? Then you'll still have 1.25 amps of idle current and only 6 pF of input capacitance.
Charles Hansen said:
Well if I'm going to do that I might as well just leave the FET out and have 0pF of input capacitance.
se
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