Hi there
I need some info on a semi-conductor simply marked as "K118" in a tube pre-amplifier (feeding one half of a 12AX7 tube - two units for the single tube).
Is this some kind of regulator? or what? 😕
I have searched and Googled but couldnt find any concrete info.
D
I need some info on a semi-conductor simply marked as "K118" in a tube pre-amplifier (feeding one half of a 12AX7 tube - two units for the single tube).
Is this some kind of regulator? or what? 😕
I have searched and Googled but couldnt find any concrete info.
D
AndrewT said:
Could be - I am not sure. It is a tiny unit with three pins like a TO-92 package but squared off at the top.
D
That's the standard marking for the 2SK118 look on top for the "color" grade, it will be a single letter.
For us that might mean year 2000 week 46 date code. Pretty easy to test non-destuctively with a voltmeter.
I did download the 2SK118 data sheet and it seems like it. Certainly looks the same.
Now what do you think it would function as? Buffer amplifier or voltage regulator?
D
Now what do you think it would function as? Buffer amplifier or voltage regulator?
D
Constant current source. Active load for the the 12AX7. IDSS @5.6mA matches quite nicely the expected plate current of 1-2mA.
You can verify this from your boards - there should be a resistor between gate and source and the fet should be the plate load of the tube. Well, just a guess.
You can verify this from your boards - there should be a resistor between gate and source and the fet should be the plate load of the tube. Well, just a guess.
a CCS provides a very high impedance load (at least a few megohms) without acting like a resistor of the same value. if you had a 10Meg resistor in the circuit, the tube would have very little voltage on the plate, and not enough current to really work right. the CCS allows the tube to work at a voltage and current it's happy with, but provides a very high impedance, which makes for lots of gain. it's also known as an "active load". the resistor from source to gate sets the operating current of the transistor. a CCS can also be made from half of a 12AX7, but the FET is inexpensive and simple, and works well.
if you get stuck trying to find the 2SK118, you could replace it with a 2N5484, which has an IDSS of 6.75ma. i think the pinout is a bit different, but it should be on the data sheet.
if you get stuck trying to find the 2SK118, you could replace it with a 2N5484, which has an IDSS of 6.75ma. i think the pinout is a bit different, but it should be on the data sheet.
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