The Fullerwell

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crgfrench
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Re: The Fullerwell

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For build #2, on the TubeDepot 5E3+ board, I decided to use “Section G” of the board for my V1 pin 3 (cathode) bias resistor and bypass cap. In a normal 5E3 build both cathodes of V1 share a common set of these which is found on the far right side of most boards (section “K” of the TubeDepot PCB). But the Fullerwell gives a Tweed voice to the Bright input and a Plexi voice to the Normal input by separating these cathodes and giving them appropriate value passives for each tone. I used section K of the board for the American channel (pin 8 of the 12AY7) but then — where to put my British bias/bypass for pin 3? So I see TubeDepot has a 2.7k resistor in the feedback circuit, with some holes for the NFB jumper and an unused ground point right next to it... super convenient since my pin 3 bias resistor is 2.7k. So, up it goes, erect and vertical and my 0.68 uF bypass cap standing up next to it in the jumper hole. My NFB circuit differs from this one anyway so I can build that off-board — it’s only one resistor. I put a loop in the ground leg of the cap to solder the resistor low side into. Here’s an image of how it turned out.
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Re: The Fullerwell

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Why does the Fullerwell use a JJ ECC823 oddball tube in the second preamp socket?

Glad you asked!

With a Cathodyne PI using only a single triode, the other triode is for gain. A 12DW7 is a nice option here since there is a high-gain (100x) triode like a 12AX7 and a low-gain triode (17x) like a 12AU7. The low triode is great for the PI function as it’s very stable and clean and the high gain triode is great for the gain function. JJ makes a 12DW7 called the ECC832 with the high gain triode wired for pins 6,7 & 8 and the low gain triode wired on 1,2&3, like a standard 12DW7. I had my socket wired with the PI on pins 6,7&8 already so I got the “reverse-wired” ECC823 from JJ.
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Re: The Fullerwell

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CE9F75FC-BCE7-4875-86FA-5AAF14CD0D7B.jpeg
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Re: The Fullerwell

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Here is the Bill of Materials I set up on Mouser.

https://www.mouser.com/ProjectManager/P ... 8010b0375d

Includes everything you need for about $400, except the board, speaker, tubes and sockets, all of which you can get from Tube Depot for an additional $200ish.

...and also the cabinet, which you would make, naturally (I'm using a Fender Tweed briefcase for this next one). Oh and a chassis; For my Blues Briefcase I'm using a bread loaf pan from Target, $1.48 each. You might want to use a Hammond 1444-10 enclosure.

This version allows you to run Class A or Class AB ...it has a DPDT switch between the single- and double-ended output transformers. You could just build it one way or the other and save some $ by only using a single OT. For this briefcase I'm using Hammond iron, if you want Heyboers the PT is HT6179 and the OT is HT6135 for Class AB, I'm not sure whether Heyboer makes a single-ended OT equivalent to the Hammond 125FSE but they might.

For the tubes I recommend JJ ECC83S preamp gain, JJ 12DW7 phase inverter, and JJ EL844 output. You could use Mullards or whatever.

Board:
Tube Depot Tweed 5E3+ or just make an eyelet/turret board.

Speaker:
Celestion G10M
Or
Celestion Ten-30

You could obviously use a 12” speaker instead, depending on your choice of cabinet; the 12" ones are too deep to fit inside this Fender tweed briefcase. If you like alnico, use a Jensen P12R; if you prefer ceramic, use a Celestion G12M. If you’re rich, use a Celestion Blue.

Tubes:
JJ brand
ECC83S (1ea)
12DW7 (1 ea)
EL844 (2ea)

It’s a 15 Watt amp with EL844s. You could boost it to 18 Watts by using EL 84s instead. No need to re-bias, it’s a cathode bias design.

This one uses diodes for the rectifier but you could use an EZ81 if you wanted; I'm trying to minimize heat inside the briefcase so 4 tubes is better than 5 in this regard.

Sockets:
Belton Micalex noval

There are about 200 solder connections.
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Last edited by crgfrench on Tue 04/23/19 11:56 am, edited 1 time in total.
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Re: The Fullerwell

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The level of detail you put into the documentation is just insane and much appreciated. Mind if I ask what you do in your day job? You barely see this level of documentation in most commercial kits.
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Re: The Fullerwell

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Thanks Returnsnull. I teach economics at Villanova and I drive the Zamboni at several ice rinks; retired from Wall Street.
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Re: The Fullerwell

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My friend in the brown delivery truck swung by today and brought me some parts for the Blues Briefcase from Antique Electronic Supply. I still need to order the power inlet panel and the iron but here is my concept laid out in the Fender Tweed briefcase.
38B933EE-D303-43A0-9B17-658FA9A10CCF.jpeg
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Re: The Fullerwell

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So today I drove over to Antek in Kearny to pick up some iron for the Blues Briefcase. John was extremely helpful and very pleasant. I'm considering the AS-1T275 and the AS-1T300 for the Fullerwell Power Transformer, and he indicated the former will deliver 280-0-280VAC from a 120VAC source while the latter will deliver 310-0-310. Since 290-0-290 is what I'm running nicely in the Denim Deluxe with Heyboer, I couldn't decide and so got one of each to try out. He says they're dead quiet with no hum. I've read they run cooler than traditional E-I wound transformers.

Sadly, his NJ production facility burned down, ruining all the winding equipment and he's now a block away in a warehouse, stocked up with his inventory and for new builds he's getting them wound in Shenzhen, China. Not sure what his plans are for retooling here...

I think the AS-1T275 may be perfect for my Blues Briefcase which will be 15W with 2 EL844s in push-pull. It might also be perfect for a regular 18W build. The AS-1T300 might need to have some 47 Ohm 5 Watt resistors between itself and the rectifier in these, I'm going to play with them both and see how they sound.

The AS-1T300 is 4.375" in diameter and about 2.5" tall, and the AS-1T275 is a bit oblong, 4.375" at its thinnest and 4.75" at its widest, and it's about 2.25" tall. They both weigh a few pounds and feel very similar in terms of mass.
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Re: The Fullerwell

Post by JMPGuitars »

The transformer didn't come with a metal plate? Normally toroids are mounted from the top: metal plate, rubber ring, transformer, rubbing ring, chassis.
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Re: The Fullerwell

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JMPGuitars wrote:
Sat 05/18/19 6:18 am
The transformer didn't come with a metal plate? Normally toroids are mounted from the top: metal plate, rubber ring, transformer, rubbing ring, chassis.
Yes they both came with the mounting hardware. You can see it in the second image.
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Re: The Fullerwell

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crgfrench wrote:
Sat 05/18/19 6:26 am
Yes they both came with the mounting hardware. You can see it in the second image.
I don't see the metal plate, it should be on top above the rubber ring.
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Re: The Fullerwell

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JMPGuitars wrote:
Sat 05/18/19 8:30 am
crgfrench wrote:
Sat 05/18/19 6:26 am
Yes they both came with the mounting hardware. You can see it in the second image.
I don't see the metal plate, it should be on top above the rubber ring.
There is a metal plate it's just underneath in this image -- it's not mounted in yet I was just showing a possible mounting position here. These each came with a bolt, washer, lockwasher, nut, 1 rubber ring (not 2) and 1 metal plate. The plate is dished rather than flat. If 2 rubber pieces are required it would be easy enough to make some extras; there is shielding around the coils so I was planning to just go rubber on bottom and plate on top. Not a bad idea to add a rubber disc on top too though -- thanks!
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Re: The Fullerwell

Post by JMPGuitars »

Ah, you tricked me. :wink: Double check that there isn't two. My most recent toroid transformer had the two rubber rings together so perfectly it looked like one until I peeled it apart. The non-flat plate is normal.

Edit: I just looked back at your photo. It does look like two rubbers.
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Re: The Fullerwell

Post by roadshow »

Not having used a toroidal transformer before, after reviewing the spec sheet for the one in question:
http://www.antekinc.com/content/AS-1T275.pdf

For 550V you'd drive both pairs of red/black primaries and tie the yellows together and run off of the whites?

Does each pair of red/black primaries drive one of the 6.3V for tube heaters?

What's the purple wire for?

Thx...
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Re: The Fullerwell

Post by crgfrench »

20190520_003520.jpg
roadshow wrote:
Sat 05/18/19 4:13 pm
Not having used a toroidal transformer before, after reviewing the spec sheet for the one in question:
http://www.antekinc.com/content/AS-1T275.pdf

For 550V you'd drive both pairs of red/black primaries and tie the yellows together and run off of the whites?

Does each pair of red/black primaries drive one of the 6.3V for tube heaters?

What's the purple wire for?

Thx...
So on the primary side you wire black to black and you wire red to red, blacks connect to 115VAC neutral line and reds connect to 115VAC hot line, purple connects to earth ground.

On the secondary LV side blue/ green is filament heater supply 6.3VAC;

On the secondary HV side connect one white to yellow for center tap and the end white & yellow gives you 275+275VAC
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Last edited by crgfrench on Sun 05/19/19 11:40 pm, edited 1 time in total.
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Re: The Fullerwell

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JMPGuitars wrote:
Sat 05/18/19 3:41 pm
Double check that there isn't two. My most recent toroid transformer had the two rubber rings together so perfectly it looked like one until I peeled it apart. The non-flat plate is normal.

Edit: I just looked back at your photo. It does look like two rubbers.
Yes -- I finally had a chance to look again and there are 2 rubber discs with each transformer.
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Re: The Fullerwell

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crgfrench wrote:
Sat 05/18/19 5:22 pm
20190520_003520.jpg
roadshow wrote:
Sat 05/18/19 4:13 pm
...after reviewing the spec sheet for the one in question:
http://www.antekinc.com/content/AS-1T275.pdf

Does each pair of red/black primaries drive one of the 6.3V for tube heaters?
On the secondary LV side blue/ green is filament heater supply 6.3VAC;
Note, although the datasheet and my wiring diagram show 2 pairs of blue and green wires on the secondary, the toroid I received has a blue-green pair followed by a brown-orange pair; use the former for the pre & output filaments and the latter for the EZ81 filaments.
20190520_011659.jpg
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Re: The Fullerwell

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JMPGuitars wrote:
Sat 05/18/19 3:41 pm
Ah, you tricked me. :wink: Double check that there isn't two. My most recent toroid transformer had the two rubber rings together so perfectly it looked like one until I peeled it apart. The non-flat plate is normal.

Edit: I just looked back at your photo. It does look like two rubbers.
2 rubbers are safer than 1 rubber!
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Re: The Fullerwell

Post by JMPGuitars »

crgfrench wrote:
Mon 05/20/19 12:31 am
2 rubbers are safer than 1 rubber!
That transformer won't be feeling a thing.
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Re: The Fullerwell

Post by Daviedawg »

Just to reaffirm what has been said on a thread at PPWatt.com, this site was set up and has been managed over the years for discussion of the Marshall 18 watt design and derivatives. The Fullerwell discussions have been very interesting with plenty food for thought as well as there being a clear desire for detail knowledge. So the thread has stayed here and run. But the design would not strictly be deemed a derivative of the Marshall 18 Watt.

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