I've got about 100 each:
J201- dark, clip easy, easy to work with, voltage forgiving from what I can tell.
MFP102 Bright clear, tougher to bias, harder to clip, not too voltage forgiving, strong output. (me like)
BS170... ??????? can't get them to work. I tried many pinout variations, disposing of each transistor
in case I blew it up trying a pinout. The are apparently fairchilds.
Are they a pain to get working? How do they sound and perform?
I heard they sounded a bit mettalic.
Can they be used in a soft clip circuit?
It looks like I will have to mix fet types to achieve my goal. I'm thinking the BS170 might work well in distortion
producing gain stages.
JFETs and MOSFETs sound similar but quite different little devices.
Your going to have to set up your circuit differently to handle the BS170s. It is not a direct drop in replacement for a JFET.
Here's a hint...
Search for "static sensitive" ;)
Are you replacing a Jfet by a BS170? You can't do that unless you have a voltage divider made by 2 resistors (one from G to ground, other from 9V or D to G) and an input cap. Then you have to bias it (adjust 9V to D resistor till you measure 4.5 - 5V from D to ground).
Maybe I have understood wrong, are you uding them in the clipping section? If it's that way, D and G are soldered together, S is the other side of the MOSFET diode.
I have a test board with a pair of 201's, a pair of MFP102's with trimpots etc for playing with. I was trying to add a set of bs170's.
I am not trying to sub mosfets for fets. These are stand alone buffers to listen to and get a feel for what works and what doesn't.
I tried few configurations found on the web and all I gould get to pass audio was an attenuator.
Is there any way to test with a vom to ensure the pinout as fairchild apparently has at least 3 different pinouts.
I think that's my main issue.
Toney. I have a nice little antistat mat and armband. :P
I have a whole bunch of BS170. I was planning on making an SHO. Not one of them works.
@rousejeremy
I usually prepare the joint by soldering it and then poking a hole through the molten solder with a bamboo skewer. I put the Fet in and add a heat sink and then solder it for as little time as possible. Maybe 1/2 second. bang and out.
They are sensitive little darlings and will pop like a grape unless you are really careful. That on top of the static sensitivity.
You need to handle both these parameters when dealing with them.
Then they are great.
@screamersusa
Nice. Sounds like you are onto that part of it.
Perhaps build as simple, reliable booster such as a Sho type. No special biasing requirements. You'll soon get 'em going.
MOSFETs require a small dc voltage on the gate in order to bias properly, unlike JFET gates which can be referenced to ground. Look up a BS170 datasheet and the "threshold voltage" (Vth IIRC) is specified there. IIRC, it's 2V. I have set this up from 2-4.5v and never had an issue getting a BS170 to turn on. You will need dc blocking via a coupling cap on the input since there is a dc voltage on it, in this case.
I don't know if this helps, but usually the pinout is backwards compared to a normal bipolar transistor.