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Post subject: Fender Pro Junior Noise
Posted: Wed Jan 30, 2013 10:41 pm
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I have a Fender Pro Junior that I purchased in 2005. I gigged with the amp on at least a weekly basis until 2011, when it suddenly developed a very bad hiss/buzz. The noise makes it unusable for any close-mic'd work, which is a real shame.
I'm hoping someone's been able to fix this and has some advice. Here are the details and what I've done so far:

-The noise is the same regardless of volume or whether a cable is plugged in
-Pulling tubes one at a time, the noise goes away completely when V2 (phase inverter) is removed
-I have re-tubed the amp
-The 47uf capacitor at C15 was going bad, so I replaced it
-Installed the Formel Standard Pro Junior Mod (changes some of the key resistors to metal film, improves a few caps, and dresses the transformer wiring)*

*Side note: while this mod did not fix my noise problem, the amp now sounds FANTASTIC, so I'm even more bummed about not being able to use it

Thanks in advance for any advice you might have. I miss using this great little amp!


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Post subject: Re: Fender Pro Junior Noise
Posted: Wed Jan 30, 2013 11:06 pm
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Welcome to Forum! Me thinks if you replaced C15 (first stage main filter cap) -- you may need to replace ALL main power supply filter caps (C16-C18).


http://ampedia.redbeartrading.com/data/ ... _schem.jpg


After, check the idle bias --- before cranking up the amp.


Good luck! :mrgreen:


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Post subject: Re: Fender Pro Junior Noise
Posted: Thu Jan 31, 2013 3:31 am
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BMW2002Ti wrote:
Welcome to Forum! Me thinks if you replaced C15 (first stage main filter cap) -- you may need to replace ALL main power supply filter caps (C16-C18).


http://ampedia.redbeartrading.com/data/ ... _schem.jpg


After, check the idle bias --- before cranking up the amp.


Good luck! :mrgreen:



+1 BMW2002Ti


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Post subject: Re: Fender Pro Junior Noise
Posted: Thu Jan 31, 2013 3:35 am
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Could be a bad power tube . New one = need bias

Need tubes contact cleaning ,

Defective solder in power supply.

And Filter cap as BMW wrote.


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Post subject: Re: Fender Pro Junior Noise
Posted: Fri Feb 01, 2013 12:47 am
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Thanks for the replies BMW and StraTele. I guess I'll order a couple new caps, and clean the tube contacts.

Has anyone had this his show up and been able to get rid of it?


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Post subject: Re: Fender Pro Junior Noise
Posted: Thu Feb 07, 2013 9:28 am
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A few updates:

-I cleaned the tube socket contacts to no avail.
-I'm working on trying to get the remainder of the mod kits from Fromel Electronics which replaces "every cap and resistor in the signal path," including new electrolytic caps. Hopefully swapping everything out will breath some new life into this puppy.

I said in my original post that when I remove V2 (the phase inverter) the noise stops. Does this point to any specific problem or area?

Thanks!


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Post subject: Re: Fender Pro Junior Noise
Posted: Thu Feb 07, 2013 10:02 am
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[quote="guitarcher"
I said in my original post that when I remove V2 (the phase inverter) the noise stops. Does this point to any specific problem or area?

[/quote]

This mean you stop the signal at the half of the amp when removing Phase Inverter tube.

This mean noise is comming from Phase inverter circuit or before ; from inputs jacks to Phase Inverter. Bad filter caps or solder in B+ circuit could make some noise too.

Everything after phase invert are OK ; Output tubes , Output transformer and speaker does not make noise.


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Post subject: Re: Fender Pro Junior Noise
Posted: Thu Feb 07, 2013 6:18 pm
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You'll find some good info in this thread :

viewtopic.php?f=13&t=56947

:wink:

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Don't leave home without it!


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Post subject: Re: Fender Pro Junior Noise
Posted: Thu Feb 07, 2013 6:26 pm
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Or on Billm's pages :

http://billmaudio.com/wp/?page_id=916

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Don't leave home without it!


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