The Fullerwell

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crgfrench
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The Fullerwell

Postby crgfrench » Tue 01/22/19 11:35 pm

Hi guys here is an 18 watt circuit I designed, I call it the “Fullerwell”. I just finished the build and it sounds delicious. Slightly different than a stock Marshall, this has a modified 5E3 Tweed Deluxe preamp (yes it’s a cathodyne PI not a long tail pair) mated to a Marshall model 1974 output section and rectifier. All the sordid details in the video, feel free to use your pause button and screen capture. https://youtu.be/zD20k6-d59Q
Would appreciate any feedback!
Last edited by crgfrench on Wed 01/23/19 12:51 am, edited 1 time in total.
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Re: The Fullerwell

Postby crgfrench » Tue 01/22/19 11:41 pm

Here’s a clip of the Fullerwell in a 1x12 “Denim Deluxe” I just finished, sorry the guitar’s out of tune and my playing is lame. This is the British channel basically dimed on gain and master volume.
https://youtu.be/HJ9cEkOMcJ4
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Re: The Fullerwell

Postby crgfrench » Wed 01/23/19 12:49 am

Here are the voltages:
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Re: The Fullerwell

Postby Daviedawg » Wed 01/23/19 4:21 am

Hi Craig. It is great to see a novel approach to building the amp. We've seen plenty variations on a theme but no build I can recall as radical as yours. Did you come across any serious issues with your layout?

Dd
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Re: The Fullerwell

Postby crgfrench » Wed 01/23/19 10:20 am

Thanks! I came at it from a different perspective and found this site along my learning curve— my original plan was simply to build an all-noval version of a 1x12 Tweed Deluxe.

I did run across 3 issues so far: 1) my negative feedback circuit squeals so I need to swap the OT primary wires on pins 7 of the 6BQ5s; there is a moderate 60Hz hum I’d like to reduce so I’ll play with the PT location; and 3) my American channel (Tweed voice) isn’t working so I may have made a design or construction error. But the British channel (Plexi voicing) works fine so I was pretty happy with the first powerup overall.

I have learned a lot from your site so thank you for all of your efforts and sharing here at 18Watt!
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Re: The Fullerwell

Postby crgfrench » Thu 01/24/19 10:54 pm

In the slides there are a few insignificant errata, here are a few I know of and I'd appreciate it if anyone spots something that looks off just let me know, thanks in advance.
Errata:
1) slides 5&6, I didn't have all of the necessary KiCad libraries so some of the switches may look odd or oddly wired in this schematic, just refer to the wiring diagrams, those are correct for the switches.
2) slides 5&6, same as previous for the transformers -- they may look funny here because I cobbled them together from other transformer symbols in KiCad. I used the Heyboers listed on slides 8 and 16.
3) slides 5&6, same as previous for the rectifier tube. I used 6CA4 (EZ81) as listed on slide 9.
4) slide 19, R7 is listed as the PI tail load BUT R7 is actually the PI bias resistor.
5) slide 19, R18 is listed as "V2 Master Volume Leak" but there is no such thing, R18 is the PI tail load resistor.
6) slide 21, these photos were taken prior to some modifications I later made, slides 22 and 23 include the modifications (added a jumper on the B+ bus, the red wire; modified high side of R24, originally had it soldered before both voltage dropping resistors but it needed to be between them, so that's why there is a black jumper wire in there now).

I think the rest is basically all OK...
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Re: The Fullerwell

Postby crgfrench » Sat 01/26/19 5:54 pm

Why is it called the “Fullerwell “?

Glad you asked!

FULLERton, California where its Tweed preamp is inspired from, plus HanWELL , London where its Bluesbreaker poweramp is inspired from.
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Re: The Fullerwell

Postby roadshow » Sat 01/26/19 8:25 pm

Pretty cool, Craig,

Especially because you're thinking outside of the box. That tolex is just awesome. The pockets are too cool, great place to keep picks, nail clippers, spare cords and so on.

FANTASTIC!!!

Bill
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Re: The Fullerwell

Postby crgfrench » Sun 01/27/19 6:37 pm

Thanks Bill! In the pockets I keep a slide, extra strings, a lighter and a flask. The Denim is from a pair of Lee jeans from the Salvation Army.
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Re: The Fullerwell

Postby crgfrench » Thu 01/31/19 6:50 pm

Further testing revealed that the American Tweed channel works fine — I just have a bad pot for its gain control. Will replace that. Also, the negative feedback circuit works perfectly. Apparently it squealed with the lightbulb current limiter but it sounds great with the amp plugged directly into wall power.
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Re: The Fullerwell

Postby crgfrench » Wed 02/06/19 10:14 am

From early feedback, here are some ways to think of the Fullerwell circuit in the Denim Deluxe amp:

a) an all-Noval tube, turbocharged 1957 Fender 5E3 Tweed Deluxe in a smaller cabinet

b) a Marshall 1965 baby Bluesbreaker 1974 with a Tweed preamp and a cathodyne phase inverter, in a much smaller cabinet and no tremolo

c) a suprocharged, class AB version of the 1964 Supro 1724T Dual-Tone in a smaller cabinet

d) a Noval tube, class AB version of the THD bivalve, in a compact 1x12 cabinet with a tube rectifier

e) all of the above
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Re: The Fullerwell

Postby JMPGuitars » Wed 02/06/19 11:35 am

The 5E3 preamp has been done a lot with the Lite 2B, but your concept takes that somewhere different, which is pretty cool.

One word of caution, I would get that breadboard out of there and build a real board. The heat/voltage/current of a guitar amp is generally greater than what those breadboards can handle, and I wouldn't consider that a reliable component.

If you need info on sourcing parts or making boards take a look here: viewtopic.php?f=25&t=25173

Thanks,
Josh
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Re: The Fullerwell

Postby crgfrench » Wed 02/06/19 4:37 pm

Thanks Josh — agreed re the board and thanks for the link. It is a perfboard laid out like a breadboard but the traces are pretty thin so I treated it like a “surface for P2P” and laid solder bridges everywhere. I half expected the board itself to fry as I brought up the variac voltages initially. I’m considering laying out a board in KiCAD that would have big fat traces and having a few fabbed at OSH Park.
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Re: The Fullerwell

Postby JMPGuitars » Wed 02/06/19 4:46 pm

The extra solder can help increase the current handling, but still probably not to a reliable level for guitar amps.

Whatever you design for your PCB, make sure the traces and trace material are significant enough for this application. One other big thing is to make sure you pick a PCB product/manufacturer that can do full through-hole vias. You don't want the vias to be surface mount only.

When I designed PCBs for guitar pedals, I used a program called "ExpressPCB." I don't know if it's around anymore, but you might be able to find it. If you know KiCAD well, or know manufacturers that work with that format, that will do short runs of boards, than you might want to order a few of them. In my experience, 3 boards costs about the same as a 1 off, but that depends on the company.
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Re: The Fullerwell

Postby crgfrench » Wed 02/06/19 6:03 pm

Thanks I will take your advice! After I finished the prototype I wanted to see how a production board looks so I bought one of Tube Depot’s 5E3 boards. Looking it over I realized you can build the Fullerwell circuit on it with a few tweaks. Here is a summary (image attached) if anyone’s interested, this would be the easiest way to build one. Of course you could make a turret or eyelet board too.Image
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