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 Post subject: Dead Easy Tweed Mod
PostPosted: Wed Dec 23, 2009 8:29 pm 
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Here is a super simple mod for your Tweed Deluxe. I love my Tweed so I had to try this mod to see if it made it any better.


From Merlin, The Valve Wizard...
Quote:
The much greater problem with the cathodyne occurs when it is itself overdriven. Because it has such a large cathode resistor only a little grid current is required to 'jack up' the cathode voltage. When driven very hard this can cause an inverted copy of the cathode signal to appear at the anode, effectively creating a sort of full-wave rectified or frequency doubled signal at the anode. This is shown in the lower photograph, and it is usually this which causes the ugly 'blatting', 'swirling' or 'grainy' sounds sometimes heard in amps using this kind of phase inverter. Fortunately, the cure is simple. We add a large grid stopper to the cathodyne, to keep this grid current in check. A value of 100k to 1Meg is usually necessary. Before you worry, this will not affect the treble response though, because the cathodyne only has unity gain! Therefore it's input capacitance is extremely low, at about 2*Cga + Cgk, which is only 4.8pF for the ECC83! This is the real 'secret' to obtaining a smooth, consistent sound from the cathodyne, no matter what kind it is. If you are using a cathodyne always give it a nice big grid-stopper. The tonal reward is startling!!! Yes I know Leo Fender didn't use any, but he wasn't designing amps to be overdriven, and this is the 21st century.


So I picked a 1/2W 470K carbon film resistor with the most mojo out of my parts bin and installed it. Easy mod, just desolder the wire on pin 7 of V2 and but the resistor in series with the wire and solder it back in place. Just like any grid stopper try and get the resistor's body as close to the pin as you can.

Anyways longest part of the mod is unscrewing the back panel. I am really liking the change so far. It is fairly subtle and it still has all the great character and qualities of a stock Tweed Deluxe. I found the mod smoothed out the distorted sound and made all the positions on my strat more natural sounding and smooth. Still has a lot of bite and growl. Seems like the amp is a tiny bit more dynamic too....


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 Post subject:
PostPosted: Tue Jan 05, 2010 3:02 pm 
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Nice. I plan on putting screen resistors on the power tubes too. I'll Let everyone know how that goes.


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PostPosted: Tue Jan 05, 2010 3:30 pm 
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Cool, sounds like a plan. The amp already has a screen voltage of course but adding a resistor might be a good idea. The screen is a grid element after all, same principles apply to control grid stoppers and screen resistors.

Are you trying to lower the screen voltage? Causer only a few mA of current will flow through your added resistors, wont drop much voltage.


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 Post subject: Re: Dead Easy Tweed Mod
PostPosted: Sat Jan 09, 2010 3:25 pm 
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kurtlives wrote:
Here is a super simple mod for your Tweed Deluxe. I love my Tweed so I had to try this mod to see if it made it any better.


From Merlin, The Valve Wizard...
Quote:
The much greater problem with the cathodyne occurs when it is itself overdriven. Because it has such a large cathode resistor only a little grid current is required to 'jack up' the cathode voltage. When driven very hard this can cause an inverted copy of the cathode signal to appear at the anode, effectively creating a sort of full-wave rectified or frequency doubled signal at the anode. This is shown in the lower photograph, and it is usually this which causes the ugly 'blatting', 'swirling' or 'grainy' sounds sometimes heard in amps using this kind of phase inverter. Fortunately, the cure is simple. We add a large grid stopper to the cathodyne, to keep this grid current in check. A value of 100k to 1Meg is usually necessary. Before you worry, this will not affect the treble response though, because the cathodyne only has unity gain! Therefore it's input capacitance is extremely low, at about 2*Cga + Cgk, which is only 4.8pF for the ECC83! This is the real 'secret' to obtaining a smooth, consistent sound from the cathodyne, no matter what kind it is. If you are using a cathodyne always give it a nice big grid-stopper. The tonal reward is startling!!! Yes I know Leo Fender didn't use any, but he wasn't designing amps to be overdriven, and this is the 21st century.


I might sound like a total DOLT, but could you rephrase all this in pratical terms for us hackers who just follow layouts and build? :roll:


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 Post subject:
PostPosted: Mon Jan 11, 2010 11:13 am 
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Not totally 100% on this (maybe Stephen or Phil could comment).


The resistor is used in conjunction with the grid leak resistor on the control grid. The grid leak and grid stopper do not attenuate the signal though like they sometimes do (at the input jacks for example).

The grid leak keeps the grid from swinging to a positive voltage. The grid stopper (the big resistor in series with your signal) prevents blocking distortion (is this the same as crossover?).

The quote basically says the tube is being stressed fairly hard. The cathode voltage is "up there". It is quite close to the anode (plate) voltage. Your output comes from the tub's plate and some how some sort of messed up double frequency effect can occur and get to the plate (output).


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 Post subject: Re: Dead Easy Tweed Mod
PostPosted: Sun Sep 05, 2010 1:20 pm 
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kurtlives modded Tweed. 470K in series with pin 7 on the PI tube.

Quote:
desolder the wire to pin 7 of V2 and put the resistor in series with the wire and solder it back in place. Just like any grid stopper try and get the resistor's body as close to the pin as you can.


Attachment:
tweed_PI_ 0011.jpg
tweed_PI_ 0011.jpg [ 113.48 KiB | Viewed 25410 times ]

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 Post subject: Re: Dead Easy Tweed Mod
PostPosted: Fri Dec 02, 2022 5:00 am 
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Good. For the power tubes, I want to install screen resistors as well. I'll report back with the results.

redactle


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 Post subject: Re: Dead Easy Tweed Mod
PostPosted: Thu Dec 22, 2022 3:07 am 
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I also plan on putting in screen resistors on the power tubes. I'll let you know what I find out.
word hurdle


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 Post subject: Re: Dead Easy Tweed Mod
PostPosted: Thu Apr 06, 2023 11:31 pm 
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It sounds like you had a successful and easy mod on your backrooms game Tweed Deluxe amp! Adding a grid stopper to the cathodyne can help to prevent overdriving and unwanted signals, leading to a smoother and more consistent sound. It's always great to experiment with mods and tweaks to see backrooms how they can improve your equipment. Enjoy your updated amp!


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 Post subject: Re: Dead Easy Tweed Mod
PostPosted: Thu Jun 01, 2023 7:29 am 
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superrobe wrote:
I also plan on putting in screen resistors on the power tubes. I'll let you know what I find out.
papa's burgeria

Actually, I have no idea about power tubes


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 Post subject: Re: Dead Easy Tweed Mod
PostPosted: Tue Aug 29, 2023 6:17 am 
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Posts: 2
The fix may be simple. Try this: move the Tone pot wire connected to its wiper from the volume pot wiper to the trim wiper.
car games


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 Post subject: Re: Dead Easy Tweed Mod
PostPosted: Wed Oct 18, 2023 1:56 am 
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Joined: Tue Oct 17, 2023 2:30 pm
Posts: 1
If you want to fix the problem, try this: move the cable that is connected to the tone pot's wiper from the volume pot wiper to the trim wiper. Play Kipas Guys Mod APK


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