Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: supro66 on November 15, 2010, 05:21:55 am
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My next amp is the 5E3 Deluxe
I found this on the net
http://online.physics.uiuc.edu/courses/phys498pom/student_projects/fall04/james_milsk_gabe_jacome/james_milsk_gabe_jacome_modified_5e3_deluxe.pdf
They modify the circuit [ James Milsk and Gabe Jacome ] Dec 7 2004
Add resisters do a feedback and remove a grid capacitor
Use a 12AX7 for a 6v6
and a stand by switch
Is this a good step
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Supro - I'm not trying to disrespect you. However, that engineering paper is misguided.
Just reading the title page, table of contents and intro, I'd say you'd be better off looking here, AMPAGE, Fender Discussion Page, etc. for tweaks to the 5E3 rather than following a couple of engineering students. I'm not trying to be a snot head, but the statement that you can't find 12AY7 tubes is just silly:
http://www.kcanostubes.com/catalog/13
OK I read a bit more. The "Uneven Frequency Response" paragraph is funny. Who says an amp should be designed to have level frequency response across the audible spectrum with the Tone knob on "5"?
They also miss the boat on guys putting a 12AX7 up front. Increased distortion is the whole point unless I'm mistaken!
Since the output of the amplifier should be simply an amplified version of the signal through the circuit, sending negative feedback should reduce the low frequencies more than the high frequencies
I'm certain that Neil Young loves it when the power tubes of his 5E3s get the snot beaten out of them 'coz they're biased so hot. Rock 'n Roll!
All that said, tweaking the 5E3 circuit so that it can use a 12AX7 up front is a reasonable adventure. Adding a switchable negative feedback loop around the power amp makes some sense if you want to be able to play nasty sometimes and cleaner at other times. Last but not least, I'd follow Hoffman's 5E3 grounding scheme long before I'd try a star ground.
Cheers,
Chip
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What Chip says! :wink:
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Thanks
That is why I am asking the PROS
I think the standby switch is a good idea ??????
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Is this a good step
Nope. If you want to mod a 5E3, you may consider the following :
Use a larger Rk - 270R, 300R, 330R/10W - for the 6V6GTs
Replace the 5K between plates and screens nodes by a >3H choke and add 470R/3W screen resistors
Use a larger cap at C1, 33µF is fine with 5Y3GTs
Lower coupling cap values from 100n to 22 or 47n
Add a 330K stopper in the cathodyne gain stage
Split the RC cathode load for V1, use 1K5 with 4µ7 in // on normal, 1K5 // 2µ2 on bright
Add a filtering node for V1
Lift the heaters by >40V
...
You may also consider more modern board designs. Doug's version is fine, you may modify it as you wish, but when used in an original tweed chassis, the B+ bus comes much too close to the input jacks for my liking.
You'll find below a pix of my own EVO version, with all the bells and whistles, in the same form factor as the original.
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FYL, I really like your layout.
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I really like your layout.
Thank you. Clean and simple. I took the pic while it was still an unfinished proto. The current version uses a slightly narrower spacing for C1 and C2 in order to gain 5 mm - a boon in a cramped tweed chassis.
If you build it, don't forget the straps below the board. Red for B+, using 600V wire, green for signal, not critical.
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Yeah I get it. I figured those were under board.
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FYL - that layout is outstanding IMHO!
Add a 330K stopper in the cathodyne gain stage
Can you explain where the grid stopper goes in the circuit and what it does?
Thanks,
Chip
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Is this a good step
You may also consider more modern board designs. Doug's version is fine, you may modify it as you wish, but when used in an original tweed chassis, the B+ bus comes much too close to the input jacks for my liking.
You'll find below a pix of my own EVO version, with all the bells and whistles, in the same form factor as the original.
I picked up this at tubedepot
http://www.tubedepot.com/pcb-5e3-err.html
And the Chassis from you know who
Right here at HIS store
Doug has a ground switch
this has a standby switch
(http://i282.photobucket.com/albums/kk243/supro66/AMPS/5E3ampstandbyswitchhoff.jpg)
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I say build it stock and enjoy the tone.Then learn how the interactive volume controls work to get the most from a 5E3.
Then learn how to use your guitar's volume control to get the most pristine clean tones from the 5E3.
Those mods make the amp into something else other than a 5E3.
I've built quite a few 5E3's and the only thing I would ever do is possibly add a choke.Most of the time I leave it alone.
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FYL - that layout is outstanding IMHO!
Thank you. Here is the template as well as a drilled board. Cap values are indicative, you may - and should - play with them in order to voice the amp.
Add a 330K stopper in the cathodyne gain stage
Can you explain where the grid stopper goes in the circuit and what it does?
The cathodyne is quite farty at high levels, with some nasty disto when overdriven. The wise old men in white with pocket protectors knew that, but didn't care as the amps were gently used by gentle players. Today is different, with full disto and overdriven amps...
Merlin was the first to suggest adding a grid stopper resistor between the gain stage and the PI itself. I did a few tests, and, yes, this trick is very effective.
"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."
http://www.freewebs.com/valvewizard/cathodyne.html
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FYL - do you put big grid stoppers on the 6V6s as well?
Thanks for sharing!
Chip
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Quote:"The cathodyne is quite farty at high levels, with some nasty disto when overdriven"
Only if you expect too much bass from this small amp.I don't.The 'fartiness' is part of the charm of the 5E3 IMHO.Hot humbuckers and too hot single coils are the problem.With vintage pickups this is not an issue at all.
I dislike the tones using hot output pickups.If you want to make the 5E3 into something else,by all means go for it.Want to revel in the vintage tone?Leave it be.
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do you put big grid stoppers on the 6V6s as well?
The usual 1K5 are OK for most players, some amps used by Neil Youg wannabes with everything on 12 need larger stops, 100 K or more.
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If you want to make the 5E3 into something else,by all means go for it.Want to revel in the vintage tone?Leave it be.
Agreed. But what is vintage tone?
The EVO keeps what is good tone-wise in a 5E3 and takes care of most of it's defects. Disto is cleaner, sound can be raunchier or smoother, dynamics are better, noise is much lower. This isn't a modern sterilized version, but an evolution. Think AC Cobra with a better chassis and better brakes, no ABS or automatic anything, no gizmos, just enhanced performance.
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Interesting.Can you show a shot of the board wired into the amp?
Where does this 'grid resistor' that Merlin talks about go in the circuit?In series with the grid to the existing PI?
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PI grid stopper: pin 7 of the PI. I just take the wire from the board that goes to the PI's grid and replace it with the resistor. I put a 100K in my 5E7 and a 220K in my 5F4. To my ears the amp's clean layer of tones become a little louder and sweeter sounding.. Both amps sound more defined and there's more of that lovely swirl and bloom at all volumes while retaining the touch sensivity.
My suggested 5E3 mods:
.022uF coupling cap on the bright channel.
Pull the bright channel from the shared 820R/25uF cathode resistor/cap and use a 2.2K/.68uF on pin 8 of V1. (play hot pickups/humbuckers through the bright channel, strats tele's through the normal ch)
220K grid stopper on the PI as described above.
300R/25uF on the 6V6 cathodes.
And... If you want to add NFB, why not make it switchable? Check this out:
http://www.tone-lizard.com/Mods_and_Odds.htm (do a search on "feedback circuits can get complicated", about 3/4ths way down the page) This section describes a very easy footswitch mod that lets you switch NFB in and out. What you'll get is a rhythm/hot solo - volume/gain boost switch. For those of us who know, a 5E3 is just not a 5E3 with NFB... Just like a vox ac30 wouldn't be a vox ac30 with NFB.. At least give yourself the option of being able to play through the amp without NFB engaged.
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Interesting.Can you show a shot of the board wired into the amp?
Hmm, not at this time. I don't have pix of mounted boards in my archives and the next builds are scheduled for next week.
Where does this 'grid resistor' that Merlin talks about go in the circuit?In series with the grid to the existing PI?
Yes. Cf. the enclosed schemo.
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Thanks FYL,
I'm certainly game to try this out.I have a Princeton Reverb build on the go and will report back with the tonal results.
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... However, that engineering paper is misguided. ...
Well, it is what it is.
That paper is posted on the internet (by a school...) because it is a great example of what it is intended to be. And that is an engineering paper written by a couple of guys who like guitars and amps which outlines a "problem," a set of proposed solutions, testing data, cost impacts and a conclusion.
They could have gotten the same grade by writing a paper on the choice of metals to deposit on an IC substrate while manufacturing bluetooth antennae. They thought a 5E3 Deluxe would be a more fun paper to write.
In all, I agree with Chip and FYL on the whole thing.
And after all... if using a 12AX7 in the first tube position is a problem, why did they not simply knock its gain down to 12AY7 level? Bear in mind that we're not seeing all the red ink corrections written by their professor.
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While we're tweaking the Tweed Deluxe, what are the pros (and cons?) of adding a choke to the power rail?
Does it affect sag in the preamp?
Touch sensitivity?
Improve power supply noise rejection?
Thanks,
Chip
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Thanks FYL,
I'm certainly game to try this out.I have a Princeton Reverb build on the go and will report back with the tonal results.
Tonal results would be greatly appreciated.
I tried to learn something applying my oscilloscope to a real Princeton Reverb's phase inverter in THIS THREAD (http://www.el34world.com/Forum/index.php?topic=10210.msg93242#msg93242). Don't think I accomplished much though. I'm due to go back inside my Prankster Reverb derivative, so this merits more experiments.
Cheers,
Chip
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While we're tweaking the Tweed Deluxe, what are the pros (and cons?) of adding a choke to the power rail?
Does it affect sag in the preamp?
Touch sensitivity?
Improve power supply noise rejection?
I'd say oh so slightly more powerful, brighter/tighter/more transparent sound, mo' dynamics/better response and lower noise.
Cons: choke cost, more holes to drill, slightly more complex cabling, can be a source of noise if ill-mounted.
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While we're tweaking the Tweed Deluxe, what are the pros (and cons?) of adding a choke to the power rail?
I did this on a 5E3 and found that the amp went better with an un-bypassed 4k7 between the screen node filter cap and the screens in CLC mode.
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Slight derail...
FYL, your 5E3 layout reminds me of a 18 watt layout I saw a few years ago.
I can't remember who's design it was, but I like the clean look of it.
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I can't remember who's design it was, but I like the clean look of it.
Barry "Loverocker" Plows at Ampmaker (UK).
http://www.ampmaker.com/
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It look like I won it :grin:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180586372052&ssPageName=ADME:B:BCA:US:1123
I now have two to build
O happy retirement :laugh:
I am getting to old to carry
I am building two heads and two speaker cabinets
cut the weight in half :undecided:
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FYL - that layout is outstanding IMHO!
Thank you. Here is the template as well as a drilled board. Cap values are indicative, you may - and should - play with them in order to voice the amp.
Add a 330K stopper in the cathodyne gain stage
Can you explain where the grid stopper goes in the circuit and what it does?
The cathodyne is quite farty at high levels, with some nasty disto when overdriven. The wise old men in white with pocket protectors knew that, but didn't care as the amps were gently used by gentle players. Today is different, with full disto and overdriven amps...
Merlin was the first to suggest adding a grid stopper resistor between the gain stage and the PI itself. I did a few tests, and, yes, this trick is very effective.
"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."
http://www.freewebs.com/valvewizard/cathodyne.html (http://www.freewebs.com/valvewizard/cathodyne.html)
Edit; Untangled quote. Willabe
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FYL - that layout is outstanding IMHO!
Thank you. Here is the template as well as a drilled board. Cap values are indicative, you may - and should - play with them in order to voice the amp.
Add a 330K stopper in the cathodyne gain stage
Can you explain where the grid stopper goes in the circuit and what it does?
The cathodyne is quite farty at high levels, with some nasty disto when overdriven. The wise old men in white with pocket protectors knew that, but didn't care as the amps were gently used by gentle players. Today is different, with full disto and overdriven amps...
Merlin was the first to suggest adding a grid stopper resistor between the gain stage and the PI itself. I did a few tests, and, yes, this trick is very effective.
"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."
http://www.freewebs.com/valvewizard/cathodyne.html (http://www.freewebs.com/valvewizard/cathodyne.html)
Edit; Untangled quote. Willabe
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I'm kind of glad you dug up this old thread, but was there a question or contribution?
Respectfully,
Chip