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Post subject: fender 75 tone stack wiring
Posted: Tue Aug 28, 2012 12:34 pm
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The schematic does not show the the wiring like a layout drawing... Is anybody familiar with the stock tone stack wiring... Somebody was in there and hacked it... The tone stack has pull boost pots.. 250k bass 10k mid 250k bass(not your average configuration)... Any help would be really appreciated...thank you..


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Post subject: Re: fender 75 tone stack wiring
Posted: Tue Aug 28, 2012 2:05 pm
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Hi jcosbar,

The stock amp has bass, mid and treble boosts, with pot values as you've described. The schematic shows this, what is your question?

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Post subject: Re: fender 75 tone stack wiring
Posted: Tue Aug 28, 2012 4:04 pm
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shimmilou wrote:
Hi jcosbar,

The stock amp has bass, mid and treble boosts, with pot values as you've described. The schematic shows this, what is your question?


My guess is he doesn't know how to read a schematic.

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Post subject: Re: fender 75 tone stack wiring
Posted: Tue Aug 28, 2012 6:06 pm
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Well Bill,the schematic and a layout drawing are totally different.. look at the schematic and tell me where the two wires for the wipers go, mid and treble pots, please.. It doesn't show it on any fender schematic for any amp....


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Post subject: Re: fender 75 tone stack wiring
Posted: Tue Aug 28, 2012 6:48 pm
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Ah, I see.

Yes, although not exactly shown, the wiper of the pot will be connected to one end of the pot in order to get the variable resistor shown. Other schematics are more clear about where the wiper connects.

And, the switches aren't shown as being connected to the pots either. That is a little different also, as some schematics will show the connection by using a dotted line connecting the pot and switch.

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Post subject: Re: fender 75 tone stack wiring
Posted: Tue Aug 28, 2012 7:33 pm
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jcosbar wrote:
Well Bill,the schematic and a layout drawing are totally different.. look at the schematic and tell me where the two wires for the wipers go, mid and treble pots, please.. It doesn't show it on any fender schematic for any amp....


Right. Like I said. You don't know how to read a schematic. When a pot is shown in a schematic like this:

Image

it is called a rheostat and is actually wired like this:

Image

The treble pot is clearly shown how it is connected.

Granted the boost switch is a little ambiguous, but since the switch is really not part of the midrange pot function (the pot shaft is just the actuator so to speak) it could be shown with a doted line as shimmilou stated, but doesn't have to be.

http://ampwares.com/schematics/fender_75.pdf

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Post subject: Re: fender 75 tone stack wiring
Posted: Wed Aug 29, 2012 5:37 am
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Thank you, for your answer... What I need is a layout drawing, for the mid and bass pots. from the eyelet board..there are 10 connection points, 5 on each pot, 3 are the pot lugs and 2 are for the switch... This is a very unusual circuit. Ed Jahnes AKA rocket scientist .. Thank you..


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Post subject: Re: fender 75 tone stack wiring
Posted: Wed Aug 29, 2012 7:16 am
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jcosbar wrote:
Thank you, for your answer... What I need is a layout drawing, for the mid and bass pots. from the eyelet board..there are 10 connection points, 5 on each pot, 3 are the pot lugs and 2 are for the switch... This is a very unusual circuit. Ed Jahnes AKA rocket scientist .. Thank you..


You're welcome.

I have not been able to find a layout drawing. However, knowing what you know now about schematics and rheostats, you should be able to trace the wiring between the pots and the board to the other components. You really don't have far to go. Perhaps you can post a photo of the area in question.

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Post subject: Re: fender 75 tone stack wiring
Posted: Wed Aug 29, 2012 12:53 pm
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I would think by reading the schematic, anyone would be able to do a layout drawing from it.. Two rheostats(pots) Bass 250k and mid 10k and the fly wires from the eyelet board?


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Post subject: Re: fender 75 tone stack wiring
Posted: Wed Aug 29, 2012 1:05 pm
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jcosbar wrote:
I would think by reading the schematic, anyone would be able to do a layout drawing from it.. Two rheostats(pots) Bass 250k and mid 10k and the fly wires from the eyelet board?


Yes, you should be able to do that. :wink:

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Post subject: Re: fender 75 tone stack wiring
Posted: Wed Aug 29, 2012 5:53 pm
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I can't transpose the schematic to a layout... my friend who is 75 and has been building fender amps since the 70's can't either...I'm his understudy for 5 years now.... I'm 57 and a fulltime firefighter and electrician... I've got at least 15 amp builds, i've done too...Fender deluxe ,super bassman,princeton, marshall plexi jtm 45, ken fisher trainwreck etc... you can see my stuff on facebook...jeff cosbar.... The fender 75 is a very difficult circuit.... I need a stock configuration wiring layout of the mid and bass potentiometers... does anybody know about these amps, please.. thanks "crobar" tone zone...


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Post subject: Re: fender 75 tone stack wiring
Posted: Wed Aug 29, 2012 6:13 pm
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I can't find a wiring diagram either, but I honestly don't know what your question is. With the exception of the pull boost on the midrange, the tone stack is a standard Blackface tone stack. The power amp appears to be ultralinear, but you are not asking about that. So I'm not sure how to try and help you.

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Post subject: Re: fender 75 tone stack wiring
Posted: Thu Aug 30, 2012 2:47 pm
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It is not a standard blackface tone stack.. I wired it as such... No good,it sounds like $@! like that...... I've been asking for a layout drawing of the bass and mid controls... If its so easy to transpose it,please do by all means.... A drawing of the wires from the eyelet board to the mid and bass pots... The wiring to treble pot was not touched.... The wiring to mid and bass was changed..... It is not standard blackface wiring either.... It's only 10 connection points... Thanks...


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Post subject: Re: fender 75 tone stack wiring
Posted: Thu Aug 30, 2012 4:43 pm
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Not much choice here other than to use a multimeter and the schematics to check continuity to figure out the circuit. Make sure that the power is off, amp unplugged from electricity, and caps discharged before proceeding. For each pot, the three terminals in a row are the pot connections, and the other two terminals are the switch.

For example, find the 250 pF cap connected to the treble pot. One side of that cap will connect to a 100K resistor and the other side will connect to one side of the treble pot. The other side of the treble pot will connect to one side of the bass pot and to a .1 uF cap. Then the other side of the bass pot should connect to one side of the mid pot and to a .047 uF cap. Continue in this manner, step by step, and you will figure it out.

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Post subject: Re: fender 75 tone stack wiring
Posted: Fri Aug 31, 2012 9:46 am
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Ring it out eh... This forum is a waste of time..All I get is a run around.. You're telling me I can't read a schematic,a simple rheostat?... Try building and amp from a schematic... A Layout drawing shows where everything goes,I need a layout of two rheostas bass and mid..And where the connections emanate from and to... For those few, who can transpose schematics, to accurate layouts...Bravo... I'm not wasting my time here anymore.... The Fender 30,75,140 are real complicated circuits not Blackface either, Ed Jahns the nasa rocket scientist, who hated overdrive designed them ........The only Fender circuits, like no other Fender amps.. :?:


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