Jfet's book in public domain https://ia801000.us.archive.org/5/i...e_-_Junction_FETs_Theory_and_Applications.pdf
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Hi
I just need one FET to put in a Tube-I-Zator board I bought some years back and of course the BOM nominates the 2SK170BL!
I'm trying to do this on a budget and I'm not keen on spending money on a bunch of high end rare FETS which I may never use.
This is probably sacrilegous but is there an acceptable substitue that I could just buy from Mouser for a buck or 2?
I just need one FET to put in a Tube-I-Zator board I bought some years back and of course the BOM nominates the 2SK170BL!
I'm trying to do this on a budget and I'm not keen on spending money on a bunch of high end rare FETS which I may never use.
This is probably sacrilegous but is there an acceptable substitue that I could just buy from Mouser for a buck or 2?
J113 is good for a lot of things, including carrying signal in the B1 Korg,
but it's not much of a substitute when you are looking for really low
noise, follower output impedance and distortion.
For Korg preamps and H2, they work fine inasmuch as these factors
aren't quite as applicable. The J113's do make decent constant current
sources though, as they are routinely degenerated enough to make
them more neutral.
I have never built it in a Tube-I-zator concept and its an old design to remember all detail, but as I see it any GR or BL should work. I would reasonably prefer 4-8mA midway Idss samples if able, for enough degeneration to still go in by the trimmer while Vgs (off) isn't high yet. So to can also enter saturation region more securely because little voltage is available across drain to source where its nested. For more info about the rest of included circuitry, or hints and tips, better contact the Tube-I-zator people.
If you believe in datasheets (I do), then 2SK170 has a breakdown voltage of 40V.
2SK373 is better at 100V, 2SK223 is slightly less at 80V.
So for 150V Vds, I personally would only use the likes of LND150.
One can of course use a LND150 to cascode a 2SK170, if one must.
Hi-Voltage JFET's
Just my 2 cents,
Patrick
2SK373 is better at 100V, 2SK223 is slightly less at 80V.
So for 150V Vds, I personally would only use the likes of LND150.
One can of course use a LND150 to cascode a 2SK170, if one must.
Hi-Voltage JFET's
Just my 2 cents,
Patrick
Only low noise low Vgs (off) parts are going to work properly there. T4 is nested in T2's Vbe in the schematic. That's all its VDS. LND150 won't get squeezed there. It will remain in Ohmic region not acting as a CCS. Even if it had the proper voltage space its a DMOSFET i.e. much more noisier than 2SK170. A viable alternative could be Toshiba 2SK880GRTE85LF or 2SK209-GR(TE85L,F) = 2SK117GR but SMD. ~Half a Euro per piece in Mouser. SOT23-3 to through hole mini converter PCBs aplenty on eBay and cheap.
Probably T4 does not break at start up all the time because Tube-I-zator is not in a theoretical phase, its a an old concept built by hundreds. Wouldn't be keeping that anode PSU through the years if breakdowns were frequent. I suppose so of course, its OT here to analyze it more. There is the Tube-I-zator thread he can ask about failure rate of T4 for certain. We talked the replacement JFET options and characteristics in detail though which is on topic.
Probably T4 does not break at start up all the time because Tube-I-zator is not in a theoretical phase, its a an old concept built by hundreds. Wouldn't be keeping that anode PSU through the years if breakdowns were frequent. I suppose so of course, its OT here to analyze it more. There is the Tube-I-zator thread he can ask about failure rate of T4 for certain. We talked the replacement JFET options and characteristics in detail though which is on topic.
I have no doubt it works.
But using a part at 4x the specified breakdown voltage, even during start up transient, is something that I personally will not do.
And none of the other parts like 2SK209 etc. has a higher breakdown voltage than 50V.
I have a private, unpublished project for ESL with +/-400V rails.
And I am using lots of 2SK170/2SJ74 in that circuit.
But every single one of them is cascoded by a HV transistor.
So they never see anything more than 10V across the D-S pins.
And they have protection diodes in addition to make sure that is the case.
But I'll sign off.
As you said, it is not relevant to this thread.
Cheers,
Patrick
But using a part at 4x the specified breakdown voltage, even during start up transient, is something that I personally will not do.
And none of the other parts like 2SK209 etc. has a higher breakdown voltage than 50V.
I have a private, unpublished project for ESL with +/-400V rails.
And I am using lots of 2SK170/2SJ74 in that circuit.
But every single one of them is cascoded by a HV transistor.
So they never see anything more than 10V across the D-S pins.
And they have protection diodes in addition to make sure that is the case.
But I'll sign off.
As you said, it is not relevant to this thread.
Cheers,
Patrick