Hello,
I am wondering what the acceptable range is, assuming matching, for these JFETs in a First Watt-type application. Can the circuits be modified to accommodate sub-optimal Idss units?
TIA
John
I am wondering what the acceptable range is, assuming matching, for these JFETs in a First Watt-type application. Can the circuits be modified to accommodate sub-optimal Idss units?
TIA
John
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Idss of 6 mA will work on these amplifiers, sometimes with small adjustment.
8 mA is a more desirable, and is the presumed default most of the time.
8 mA is a more desirable, and is the presumed default most of the time.
Excellent- thanks so much, Nelson.
I have ordered some (Toshibas) from an online seller and requested sets close to 8mA Idss (he tests at 9.00 V).
Seems a legit supplier - it is a (pro) audio manufacturer who bought the JFETs from "top-line U.S. distributors". Fingers crossed.
John
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Absolutely nothing wrong with lsk170 or lsj74, if you have trouble getting genuine toshiba parts.
Who did you get them from? The only dependable source with idss all through the sweet area I know of is Spencer. Always genuine.
Russellc
The seller is Millennia Music & Media Systems.
I got them here (hoping they were a smart buy). I note that the upper end of the Idss range is lower than when I bought. I requested mine were as close as possible to 8 mA. He as pairs as wellas quads, as well as some other FETs.
"FETs are matched in pairs to within 0.03mA Idss AND 4mV Vgs."
Toshiba 2SJ74 + 2SK170 MATCHED QUAD to 0.03mA AND 4mV 7.2mA-7.4mA Idss Range
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While they might be genuine, it's hard to believe they're new. Those legs look resistance-welded on, don't they?
(As does every other seller's on eBay; and they all describe them as "new, unused". Am I missing something, or is truth truly out of style?)
(As does every other seller's on eBay; and they all describe them as "new, unused". Am I missing something, or is truth truly out of style?)
I have bought from the guy in the past but I cannot remember if they were genuine or not. During that time, before the LSJ74 was available, I tried a few of the Ebay sellers. Most were fakes. Buyer beware on Ebay. It is always best to have matched sets but not a deal breaker if they are not. You will have more 2nd or more 3rd with a mismatched pair but it can be corrected with some source resistance if you do not like the sound. Sometime people like the sound with a mismatched pair better depending on whether you like more or less 2nd harmonic.
My vote is for LSK only for the J-fets.
My vote is for LSK only for the J-fets.
I know John La Grou personally, I remember when he bought them, and you
can bet he matches them that tightly.
Hope you are right, but if it wasnt Spencer, or that gentlman from Israel (last I checked he was running out of matched pairs in the sweet spot) there is a high likelihood of fakes.
Good luck
Russellc
Yes, it sounds as you have found a good source. These sources are rare as hens teeth. I have, and I suggest you as well, lay in a small supply to use in the amps you plan to build.
Its nice the store provides the linear versions, but I have previously inquired if idss can be requested, but never got a response. I have a couple sets of them, but have no idea where they measure idss wise.
Havent had a need to find out by measuring them, I just ordered sets measured by Spencer.
Happy amp building!
Russellc
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