Another Fetzer Valve topic...

[Noplasticrobots]

I don't know what I'm doing wrong, but my Fetzer Valve has next to no output. I don't have a volume pot on it, but that shouldn't matter. The drain is biased to 4.5 volts. I've got the N channel MPF102 from Rat Shack in there. No subs on any parts. With the flat side up, from left to right the pins are drain, source and gate, correct?

[vanhansen]

Flip it around.  The pinout might be wrong.  Just a hunch.

[wampcat1]

I don't know what I'm doing wrong, but my Fetzer Valve has next to no output. I don't have a volume pot on it, but that shouldn't matter. The drain is biased to 4.5 volts. I've got the N channel MPF102 from Rat Shack in there. No subs on any parts. With the flat side up, from left to right the pins are drain, source and gate, correct?

Should be, but I'll be honest, I can rarely get RS transistors to work right. Aron's j201's always work excellent for me though.

I just drew a VERY crude drawing for you in paint, but it might/might not help:


Hope that helps!

Brian

[Night0wl]

I have been working on the fetzer using a MPF102 for a week trying to get it going (similar probs) and, with some advice from a friend, I changed from a trimpot to a regular 100k 16mm pot. I then set the drain to about 4.5v, measured the resistance of the pot (which was 2.2k) and then removed the pot and replaced it with a 2.2k fixed resistor. It has worked great ever since!

Also, the MPF102 doesn't give as much gain as the J201. A friend tried the same thing with a J201 and the drain was 27k! He suggested using about a 6.8k source resistor instead of a 1.5k and set about 10-12k drain if using a MPF102.

Not sure if any of this is relevant, but it may help.

Cheers
Shane

[Threefish]

You're getting a signal, so that's a start. I've built two fetzer valves with MPF102's and both worked fine, and I don't have access to J201's so I can't comment on the difference. The data sheets I've got show the J201 and MPF102 pinouts the same, so that shouldn't be an issue (I said SHOULDN'T). I've never had to check voltages at the drain – just tune them by ear, with a radio at low level into the fetzer input and the output into an amp. I've always found the turn of the pot like a switch – it works or it doesn't. Maybe Jaycar's MPF102's are better than RS's.

Eh? I'm confused by your pic Brian. Why have you got +9v going into lug 2 of the pot? Doesn't the schem say lug 1? And lugs 2 and 3 need to be linked. You're missing the 1M to ground at the gate too.

I've never run one open all the way (ie- no pot at the output), so I don't know if that's an issue. Someone more knowledgeable might advise a resistance to ground is needed at the output for...some reason [cringe].

Check your layout against the Runoffgroove one. It should work. Have you made any connections where there shouldn't be? There should only be connections where the big dots are.

[wampcat1]

You're getting a signal, so that's a start. I've built two fetzer valves with MPF102's and both worked fine, and I don't have access to J201's so I can't comment on the difference. The data sheets I've got show the J201 and MPF102 pinouts the same, so that shouldn't be an issue (I said SHOULDN'T). I've never had to check voltages at the drain – just tune them by ear, with a radio at low level into the fetzer input and the output into an amp. I've always found the turn of the pot like a switch – it works or it doesn't. Maybe Jaycar's MPF102's are better than RS's.

Eh? I'm confused by your pic Brian. Why have you got +9v going into lug 2 of the pot? Doesn't the schem say lug 1? And lugs 2 and 3 need to be linked. You're missing the 1M to ground at the gate too.

It's just implying a trim pot...lug 1/lug 2, no difference in passing the voltage. Also linking the other lug isn't going to make a difference either in this situation. The 1m to ground at the input is missing (but it WILL still work even if you don't have it), like I said, I drew this up VERY quickly, so just pretend there is one there!  

I've never run one open all the way (ie- no pot at the output), so I don't know if that's an issue. Someone more knowledgeable might advise a resistance to ground is needed at the output for...some reason [cringe].

Nope, no issue, but notice I put 'out'. That implies tonestack, volume control, etc.

Check your layout against the Runoffgroove one. It should work. Have you made any connections where there shouldn't be? There should only be connections where the big dots are.

[/quote] 

[Ge_Whiz]

Have you tried the optional reverse-threaded muffler bearings?

[burnt fingers]

I think Fletch said it best.  You're gonna need some gauze, some three in one oil and some ball bearings.  Whoooo.

Sorry guys, I couldn't help it.