2nd Gen FET question (Solved)

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Guitarman18
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2nd Gen FET question (Solved)

Post by Guitarman18 »

Inspired by the tones that Erwin and others are getting using the FET boost, I've decided to revisit my 2ND Gen and get the FET working properly.

My 2N3823 has 4 pins, but the layout/3rd Gen schem is wired with 3 pins. I realize that one of the pins is the case, but what needs to be done with this leg for it to operate correctly?

If anyone can help, it would be greatly appreciated.

Cheers,

Paul.
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Last edited by Guitarman18 on Tue Jul 04, 2017 9:12 pm, edited 1 time in total.
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davebolden44
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Re: 2nd Gen FET question

Post by davebolden44 »

ground the case
davebolden44
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Re: 2nd Gen FET question

Post by davebolden44 »

http://ampgarage.com/forum/download/fil ... &mode=view
I like this particular layout for reference, it is clear to read and works like a charm.
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martin manning
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Re: 2nd Gen FET question

Post by martin manning »

It might work fine with just GDS connected, but run the case lead to ground. I noticed the 2nd gen layout is missing an eyelet-eyelet connection and a ground. You might have to adjust the voltage divider and the source resistor to get the right bias point. See in the files section for a sticky on that.
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Guitarman18
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Re: 2nd Gen FET question

Post by Guitarman18 »

Excellent info davebolden44 and Martin.

Many thanks for that. I'll get on to it as soon as I can, and report back.

Best wishes,

Paul.
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norburybrook
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Re: 2nd Gen FET question

Post by norburybrook »

what are people using for the JFET these days the NTE452 is now obsolete.

I've got a FET board laying around I might add one to my #102.

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erwin_ve
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Re: 2nd Gen FET question

Post by erwin_ve »

I used 2N4416A. You can get them at mouser.
davebolden44
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Re: 2nd Gen FET question

Post by davebolden44 »

Its not like you cant get the nte452. I bought several recently, cant remember where. Maybe amazon
Guitarman18
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Re: 2nd Gen FET question

Post by Guitarman18 »

Hi Marcus,

I used these 2N3823;

http://www.ebay.co.uk/itm/112032431092

Having said that, I still haven't managed to get my FET board to come to life. Either the FET is not working or something else is a bit dodgey.

I'm going to completely rebuild the FET board tomorrow and find out if that helps. Dammit! :roll:

Cheers,

Paul.
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martin manning
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Re: 2nd Gen FET question

Post by martin manning »

You can disconnect the power lead and then use the battery method to power it and see if you have an appropriate value for the bias resistor. Even if there are no wiring errors, the FET must be biased correctly. I bought a bag of ten 2N3823's not too long ago from a parts dealer, and 2N4416A's are readily available (somewhat pricy, though).
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Mr. dB
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Re: 2nd Gen FET question

Post by Mr. dB »

What's a good B+ level for checking the FET board separately before installing it into an amp?
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ToneMerc
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Re: 2nd Gen FET question

Post by ToneMerc »

Mr. dB wrote: Mon Jul 03, 2017 8:57 pm What's a good B+ level for checking the FET board separately before installing it into an amp?
http://ampgarage.com/forum/viewtopic.php?f=5&t=18389

TM
Guitarman18
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Re: 2nd Gen FET question

Post by Guitarman18 »

martin manning wrote: Mon Jul 03, 2017 7:42 pm You can disconnect the power lead and then use the battery method to power it and see if you have an appropriate value for the bias resistor. Even if there are no wiring errors, the FET must be biased correctly. I bought a bag of ten 2N3823's not too long ago from a parts dealer, and 2N4416A's are readily available (somewhat pricy, though).
Thanks Martin,

I've used your 'Method to Set Fet bias and Supply voltage' before, which was very helpful. I'll revisit that for this FET board, but I think it may be more than a bias issue. I also tried dropping the 3.3M to 2M, as per Gary's suggestion 'if your FET isn't passing gas'.......

Cheers,

Paul.
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Mr. dB
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Re: 2nd Gen FET question

Post by Mr. dB »

ToneMerc wrote: Mon Jul 03, 2017 9:04 pm
Mr. dB wrote: Mon Jul 03, 2017 8:57 pm What's a good B+ level for checking the FET board separately before installing it into an amp?
http://ampgarage.com/forum/viewtopic.php?f=5&t=18389

Thank you sir.
Guitarman18
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Re: 2nd Gen FET question

Post by Guitarman18 »

The setup I have at the moment looks like this;


If anyone can see anything wrong with this picture, I'd really appreciate it. It will save me from starting a new board.

Thanks in advance for your help.

Cheers,

Paul.
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