I contacted Tony339 for a set of eight matched complimentary devices, and he went the extra mile. I provided a schematic of the circuit I was building and he tested the devices in the said circuit. He provided sensible advice, and after I had paid for the Jfets, they arrived very fast in the mail. I think the way they were packaged was excellent: they were inside a plastic holder, each pnp and npn device standing in line and labelled. I have to say, this was a lot less pain than myself buying a batch and trying to match them individually.
Awesome work, Tony!
Awesome work, Tony!
I would take these:
197 10,32 10,33 0,19% £28,00
199 10,33
196 10,34
198 10,34
Send me an email at:
tonimxp@libero.it
Thanks...
Antonio
197 10,32 10,33 0,19% £28,00
199 10,33
196 10,34
198 10,34
Send me an email at:
tonimxp@libero.it
Thanks...
Antonio
Yes, you have included postage fees. Your jfets are packaged ready to go, I will pm you when posted.
Cheers,
Tony
Degenerated matching
I have mentioned before about some issues matching these devices but for those interested here are my experiences.
Many would naturally assume a closely matched pair of K170/J74 is attained by low Idss tolerance but this is not altogether true.
These devices have different transconductance (‘gain’) curves and are therefore not true complements.
Simply matching Idss at a given Vds (usually 10v) will only give the point at which the curves meet. This also accounts for tolerance being Vds dependant – K170 Idss increases more than J74 with Vds.
Further explanation and a simple 'fix' is given by EUVL in the article ‘Input JFET Variants’, I have done a few tests myself which concur with this.
A relatively simple way of degenerated matching is to measure Idss of a J74 with around 5ohm source resistor and match this to a K170 without a source resistor. If this is done at the actual Vds of the circuit they are to be used in then the results should be pretty much spot on. Vds is given by supply voltage less the voltage drop of R drain.
For the more technical the formula from EUVL is;
Idss (2SJ74) = Id * (1 + Rs.Yfs)
where Id = Idss of the 2SK170 in this case; Rs =Source resistor value; Yfs = Siemens for 2SJ74 (approximate values can be found in the data sheet)
I have mentioned before about some issues matching these devices but for those interested here are my experiences.
Many would naturally assume a closely matched pair of K170/J74 is attained by low Idss tolerance but this is not altogether true.
These devices have different transconductance (‘gain’) curves and are therefore not true complements.
Simply matching Idss at a given Vds (usually 10v) will only give the point at which the curves meet. This also accounts for tolerance being Vds dependant – K170 Idss increases more than J74 with Vds.
Further explanation and a simple 'fix' is given by EUVL in the article ‘Input JFET Variants’, I have done a few tests myself which concur with this.
A relatively simple way of degenerated matching is to measure Idss of a J74 with around 5ohm source resistor and match this to a K170 without a source resistor. If this is done at the actual Vds of the circuit they are to be used in then the results should be pretty much spot on. Vds is given by supply voltage less the voltage drop of R drain.
For the more technical the formula from EUVL is;
Idss (2SJ74) = Id * (1 + Rs.Yfs)
where Id = Idss of the 2SK170 in this case; Rs =Source resistor value; Yfs = Siemens for 2SJ74 (approximate values can be found in the data sheet)
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