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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Thu Mar 28, 2013 10:36 pm
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Bill,

Correct! It's similar to the bypass mica pico-farad disc cap, bypassing the main GNFB resistor --- like in this AA371 Bassman.

http://ampwares.com/schematics/bassman_aa371.pdf


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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Fri Mar 29, 2013 6:38 am
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BMW2002Ti wrote:
Bill,

Correct! It's similar to the bypass mica pico-farad disc cap, bypassing the main GNFB resistor --- like in this AA371 Bassman.

http://ampwares.com/schematics/bassman_aa371.pdf


Another Fender mystery solved. 8) :D :lol:

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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Fri Mar 29, 2013 8:25 am
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Bill-
That's the one. The way it's written on the layout would suggest it was added later. Since it's tied into the feedback resistor, the PI and the speaker output, it could have an effect on voltage. Am I correct. Also? would this 'after thought' mod suggest that early silverface amps did not need this cap, but later one's did. I will say the lead dress leaves much to be desired. Chris


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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Fri Mar 29, 2013 9:44 am
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Yup, That's the one. If it was an after thought, does it mean the earlier silverface amps are OK and it was added to later amps or is it a recommended mod? Also, Since it ties into the feedback cap, the PI and the speaker terminal, would it affect voltage and bias?


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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Fri Mar 29, 2013 9:46 am
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sorry for the double post.


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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Fri Mar 29, 2013 11:26 am
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Krankster wrote:
Bill-
That's the one. The way it's written on the layout would suggest it was added later. Since it's tied into the feedback resistor, the PI and the speaker output, it could have an effect on voltage. Am I correct. Also? would this 'after thought' mod suggest that early silverface amps did not need this cap, but later one's did. I will say the lead dress leaves much to be desired. Chris


Looks to me like a poor man's presence mod. My guess is someone decided it was necessary to bypass some highs around the feedback resistor. It will probably change the loop gain a little bit. If it is easy to remove, I would try that and see if it makes a difference. Or just leave it alone if you are happy with the tone.

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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Fri Mar 29, 2013 4:06 pm
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If it ain't broke, don't fix it. Thanks for all the help. You guys are great. I don't trust the local amp techs. So, I learned how to solder, read a schematic and use a multi-meter.


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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Fri Mar 29, 2013 4:32 pm
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Krankster wrote:
If it ain't broke, don't fix it. Thanks for all the help. You guys are great. I don't trust the local amp techs. So, I learned how to solder, read a schematic and use a multi-meter.


That in and of itself can be real money-saver.

Arjay

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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Fri Mar 29, 2013 9:50 pm
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Krankster wrote:
If it ain't broke, don't fix it. Thanks for all the help. You guys are great. I don't trust the local amp techs. So, I learned how to solder, read a schematic and use a multi-meter.


As we all did. 8)

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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Sat Mar 30, 2013 4:26 am
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Indeed.

Just don't let the neighbors know that you're familiar with electronics repair.

Otherwise they'll be bringing over all manner of broken junk, expecting you to be some kind of miracle worker.

:lol:

Arjay

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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Sat Mar 30, 2013 5:44 am
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Retroverbial wrote:
Indeed.

Just don't let the neighbors know that you're familiar with electronics repair.

Otherwise they'll be bringing over all manner of broken junk, expecting you to be some kind of miracle worker.

:lol:

Arjay


Hey Arjay, your neighbor called, said something about a toaster and a blender?? :lol: :lol:

T2

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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Sat Mar 30, 2013 10:02 am
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T2Stratman wrote:
Hey Arjay, your neighbor called, said something about a toaster and a blender??


That was last month.

The gal across the street asked me yesterday if I could take a look at her microwave......

8)

Arjay

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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Wed Apr 03, 2013 10:29 am
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I didn't bring this up before about the 72' Super. One of the .1/600 coupling caps-the second one from the left has been replaced with a Sprague 418. It has the blue blobs. I have a Jupiter yellow .1/600 cap-mylar/film left over from another project. They are awesome. Should I go through the trouble of istalling it? Would it make a difference? Also, some of the carbon comp resistors in that area-47k's, 220k, 1M have what looks like dried glue on them. I have some extras, should I replace those while I'm at it? Thank in advance, Chris


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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Tue Jul 02, 2013 2:16 pm
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Totally stock and rocking 72' Super Reverb

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Post subject: Re: Blackfacing an early 1970's fender amp vs. Keeping it st
Posted: Tue Jul 02, 2013 2:22 pm
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Arjay

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