Need help ID'ing this transistor

[acorkos]

Q1 on this Fender Scorpio schematic (early solid state) says F1175. The transistor itself reads 908W38 (the 9 might be a lower case g). I can't find any info on it or cross references. I'd like to replace it, normal channel is low output, this transistor has +15vdc on all legs. Thanks for your help

[mhuss]

Nothing immediately turns up in a search, but it's only got a 30v supply, so probably any generic FET (2N7000 etc.) would work.

[Helmholtz]

2N7000 is a Mosfet. Schematic shows an N-channel Jfet. Looks like a source follower (buffer) stage. Please post full schematic.

[Jon Snell]

Try a J112 Jug Fet.

[vintagekiki]

https://music-electronics-forum.com/forum/schematic-requests/35546-fender-early-70-s-solid-state-amp-schematics
^{Fender Early 70's Solid-State Amp}
https://music-electronics-forum.com/filedata/fetch?id=867885&d=1382714594
^{Fender Scorpio Schematics}

[J M Fahey]

Q1 on this Fender Scorpio schematic (early solid state) says F1175. The transistor itself reads 908W38 (the 9 might be a lower case g). I can't find any info on it or cross references. I'd like to replace it, normal channel is low output, this transistor has +15vdc on all legs. Thanks for your help

The stamp sized tiny fraction of the schematic tells us nothing.

[DrGonz78]

Just curious... How many legs does the Jfet have on that board?

[acorkos]

2N7000 is a Mosfet. Schematic shows an N-channel Jfet. Looks like a source follower (buffer) stage. Please post full schematic.

fender_scorpio_sch.pdf

[acorkos]

Just curious... How many legs does the Jfet have on that board?

3 legs

[DrGonz78]

Okay cool. I’ve only worked on an old Fender Taurus model Zodiac amp. It has that same input jfet and it is connected to the board through a plastic mounting bracket (for lack of a better name). I was looking at old Motorola jfets from that time period that had 4 legs.

[acorkos]

Okay cool. I’ve only worked on an old Fender Taurus model Zodiac amp. It has that same input jfet and it is connected to the board through a plastic mounting bracket (for lack of a better name). I was looking at old Motorola jfets from that time period that had 4 legs.

Q1 is the one on the left which I think is the problem, Normal channel has low output. Q2 on the right is for the Vib channel, it's got the plastic bracket, wondering what it's for.

[Helmholtz]

The plastic spreaders were used as insertion aid and to ensure a minimum lead length to prevent excessive chip temperatures when soldering. They also prevent sharp lead bendings right at the component.
So I assume there should have been 2 of them.

[J M Fahey]

Itīs a simple JFET unity gain source follower.
Its job is easy so in that case, "any FET" will work, including J112 suggested by Jon Snell.
Just take care of pinout, apparently G-D-S are silkscreened on the PCB

Your symptoms might show a shorted FET *or* open R9

Turn ampOFF, wait for supply voltages to reach 0V (to drain the last drops ground +V through 100 ohm 1W or similar) and measure resistance from Q1 source to ground.

Measure from Fet leg itself to ground.
You should read 47k , within tolerance.

IF you jhave properv resistance value, then dead FET is confirmed but itīs easy to substitute.
Good luck.

[acorkos]

J112 solved the problem, thx all

[vintagekiki]

Q1 on this Fender Scorpio schematic ... normal channel is low output, this transistor has +15vdc on all legs

The most elegant way to test Q1 is to compare the voltages at Q1 and Q2.
Eventually you can reciprocally swap places Q1 and Q2 to determine the correct state Q1.

[vintagekiki]

Too late, now I noticed your previous post.