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Post subject: tone stack issue
Posted: Mon Nov 12, 2012 2:22 pm
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Rock Star
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Wondered how many of you had this issue. Where both treble and volume pots controlled the volume? And the treble pot had no effect on treble.

The way these early tone stacks were setup, if that 250 pico-farad ceramic cap fails and leaks--- that's just what happens. I think I've only seen a couple of this kinda issues in all these years. That's how good those original disc caps were made. This Pro Reverb had the cap modded out with a new one (off-shore made) to up the value to 500 pico-farads for some reason.

Too many amps on the bench, now. Back to inhaling solder fumes. :lol:

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Post subject: Re: tone stack issue
Posted: Mon Nov 12, 2012 3:18 pm
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Rock Star
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Joined: Mon Apr 05, 2010 2:37 pm
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Location: Natural Bridge, Virginia
If you are a glutton for punishment (like me), you might want to take a look at this analysis of the 5F6A Bassman and early Marshall derivative tone stacks:

http://ampbooks.com/home/classic-circui ... ack-intro/

http://ampbooks.com/home/classic-circui ... frequency/

http://ampbooks.com/home/classic-circui ... frequency/

http://ampbooks.com/home/classic-circui ... tonestack/

http://ampbooks.com/home/classic-circui ... stack-mod/

I also find this model to be useful when working with tonestacks. I have modified the Marshall model for use with the 5F6A Bassman and Blues Deluxe Reissue. I find it to be very accurate.

http://www.duncanamps.com/tsc/index.html

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Post subject: Re: tone stack issue
Posted: Mon Nov 12, 2012 5:04 pm
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Rock Star
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Bluesky, very good references. Now, I can see what the tech that changed out the 250 pico-farad disc cap was after. The OEM 0.1 mfd and 0.22 mfd caps in the stack remained the same.

Problem is, there has been a lot of posts on boards about failure in recent production disc caps. Esp silver mica type made in a certain part of the world --- where the sun rises, as it is setting on the West Coast. :D

Will look over those time-constant equations. Thanks, again!


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Post subject: Re: tone stack issue
Posted: Mon Nov 12, 2012 5:32 pm
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Rock Star
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Location: Natural Bridge, Virginia
You're welcome. Enjoy.

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Post subject: Re: tone stack issue
Posted: Tue Nov 13, 2012 5:20 pm
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Professional Musician
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Bill, I've used that Duncan calculator with good results ! Art

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Post subject: Re: tone stack issue
Posted: Tue Nov 13, 2012 8:19 pm
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Rock Star
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Location: Natural Bridge, Virginia
Its very handy. The formulas on the Amp Books site will allow you to calculate source and load impedances for the tone stack and let you get a pretty exact simulation.

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Post subject: Re: tone stack issue
Posted: Tue Nov 13, 2012 10:18 pm
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Location: Harvard IL
Yeah Bro, I'm with you!!! But this guitar picker is given to math headaches. I do appreciate the real straight info!!!! Art

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Post subject: Re: tone stack issue
Posted: Wed Nov 14, 2012 7:31 am
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Rock Star
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Joined: Mon Apr 05, 2010 2:37 pm
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Location: Natural Bridge, Virginia
aclempoppi wrote:
Yeah Bro, I'm with you!!! But this guitar picker is given to math headaches. I do appreciate the real straight info!!!! Art


That's what's nice about these calculators. They do the math for you. :D

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