I think the replacement for the 2SA1085 is a KSA992 which is available, but I don't know of an available one for the 2SC25457. (MC Preamp)
Any thoughts ?
Thanks.
Any thoughts ?
Thanks.
Thanks rsavas, - of course, - I should have searched for the KSA 992 compliment !
However they are both out of stock at B+D so I will keep searching.
However they are both out of stock at B+D so I will keep searching.
errm "You're a very nice transistor"? 🙂
More seriously the KSA992 has only 50mA current handling, the 2SA1085 is 100mA, so that's a caveat (probably not an issue for analog circuitry, but for a relay driver it might matter). The 2SA1085 is extremely quiet at 0.5nV/√Hz, so this may be an issue for a replacement device. I've measured KSA992's at about 2nV/√Hz for what its worth.
I second what Mark says , used 2SA1085 many times as long tailed pairs in power amplifiers very reliable , from what I remember JLH liked them as well.
Thanks for your replies Mark & duncan2.
These are for an MC preamp so I think the current rating is OK.
However, my local supplier has ZTX790A & ZTX690B, (maybe a newer version of the ZTX650/750), which way back, were supposed to be for this application. Hopefully these should suffice - ??
These are for an MC preamp so I think the current rating is OK.
However, my local supplier has ZTX790A & ZTX690B, (maybe a newer version of the ZTX650/750), which way back, were supposed to be for this application. Hopefully these should suffice - ??
The 790A/690B is the pair I use for high speed switching mosfet drivers so I always have them on hand. They can slug an amp of current into a decent amount of capacitance with little drive. Never thought about them for preamps. Is the noise performance especially good?
ZTX851 and ZTX951 then - lowest voltage noise available to my knowledge, < 0.28nV/√Hz at 10mA
see Ultra low noise amplifiers
and Ultra low noise amplifiers
I presume you don't need the 120V rating of the 1085/2547 for such an application?
The 851/951 do seem to be available ATM, I bought 10 of each last week.
Thanks Mark.
Where did you buy them. - I have 2 suppliers but the postage charges are excessive. I only need 10 of each.
Where did you buy them. - I have 2 suppliers but the postage charges are excessive. I only need 10 of each.
Happens to be Farnell, but I think Mouser and Digikey have stock too. But it was part of a larger order to eliminate the extra charges... I keep a list of parts-to-restock(*) and try to order less frequently to reduce postage.
The ZTX851/951 are handy to have stocked because as well as having shockingly low voltage noise they can switch several amps and are rated for base-current being 2% of collector current as a switch - for instance you can switch 1A using 20mA base current and get 0.1V saturation voltage!
(*) boring things like wires, diecast bozes, mounting hardware, stripboard, tools that you don't require immediately but can pad out an order
The ZTX851/951 are handy to have stocked because as well as having shockingly low voltage noise they can switch several amps and are rated for base-current being 2% of collector current as a switch - for instance you can switch 1A using 20mA base current and get 0.1V saturation voltage!
(*) boring things like wires, diecast bozes, mounting hardware, stripboard, tools that you don't require immediately but can pad out an order