The Fullerwell

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crgfrench
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Re: The Fullerwell

Postby crgfrench » Sun 02/10/19 10:53 pm

Here are some things I was losing sleep over, it’s my first amp build. Probably worried too much; all went pretty well.

Firing up the Denim Deluxe, What could go wrong:

Circuit could be designed poorly.

I could have done some bad soldering.

I may have used improper spec components.

The components could be placed in poor locations causing hum or noise (transformers would likely be the main culprit).

Short in circuit somewhere, or an open circuit somewhere .

I may have installed a faulty component (even if new).

Any of the passive components’ value could be too far off from spec (carbon composite resistors most likely).

I could have misconnected wiring during construction.

The board or wire can’t handle load & fries.

Poor lead dress could lead to hum or noise.

The board bus could be laid out as an improper grounding scheme.

Negative Feedback could squeal due to being in phase. NFB squeal? Reconnect Output transformer primary wires (blue & brown) to pins 7 of the opposite power tube.

Did I interpret the socket pinouts upside down (pins 1-9 backward)? Seriously doubt this but hey I guess it’s possible.

Will my lightbulb current limiter work with the variac to protect the caps at startup?

Is the NOS Tesla rectifier tube OK?

Did I wire the 3 switched tone circuits (Boost, Blend & Bright) properly?

Did I wire the rectifier vintage/modern switch properly?

Did I wire the attenuator circuit properly?

Should the pot tabs be grounded?

Is it safe to run the high voltage B+ (340VDC) to the volume pot’s rotary switch?

Should the grid stoppers be on the sockets instead of the jacks?

Should I have twisted the pin 7 wires from the power tube plates to the OT?

Should I have used shielded cable instead of the red wires to V1?

Should have used modern quiet resistors in the chassis?

Does the capacitor draining resistor ruin the circuit?

Will the 580 AC Volts & 340 DC Volts kill me?
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Re: The Fullerwell

Postby crgfrench » Fri 02/15/19 9:45 am

Quick update on the output tubes (all matched pairs, all with Mullard CV4004 in first preamp socket and JJ ECC823 in second preamp socket, with a NOS Tesla EZ81 recto):

1) JJ EL84 new production pair works well.

2) Bendix 6094 NOS pair works but oscillates at higher gain settings.

3) EH 6973 new production pair redplates and blue glow even at low gain settings.

So I plan to try a 250 Ohm 8W Brown Devil in place of the current 125 Ohm 8W to cool down the bias.

(For the 6094s and 6973s I am using noval-noval pin adapters made in China, that convert them each to the 6BQ5 pinout the sockets are wired for).
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Re: The Fullerwell

Postby crgfrench » Tue 02/19/19 5:46 pm

Image So taking Josh’s advice, I decided to build #2 using a “real” board. As I posted earlier, the 5E3+ board from Tube Depot seems like a good candidate. I got most of the passives soldered last night, here is an image of it sitting on a catalogue. For this one I kept the 125 Ohm Brown Devil; changed to Sprague from TAD filter caps; switched from orange drop 715s to Mallory 150s; and switched from carbon composite to Dale milspec for most of the 1/2W resistors.
4B3C6CB5-5DC2-4860-804F-A724D5250B70.jpeg
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Re: The Fullerwell

Postby crgfrench » Tue 02/19/19 6:00 pm

9786636F-B8CD-45CD-95CC-87978453E403.jpeg
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Re: The Fullerwell

Postby JMPGuitars » Tue 02/19/19 8:46 pm

crgfrench wrote:
Sun 02/10/19 10:53 pm
Should the grid stoppers be on the sockets instead of the jacks?

Should I have twisted the pin 7 wires from the power tube plates to the OT?

Should I have used shielded cable instead of the red wires to V1?

Should have used modern quiet resistors in the chassis?

Does the capacitor draining resistor ruin the circuit?

Will the 580 AC Volts & 340 DC Volts kill me?
I thought I already replied to this. Oops. Anyway:

Yes, ideally the grid stoppers should be as close to the socket as possible. But if it's doing the job, don't overthink it.

The voltage level coming off the OT leads won't benefit from twisting them, but people often twist them anyway for aesthetic reasons.

If the "red wire" is your input wire, then yes, shielded wire is a good idea. If you're lucky enough to not be getting noise without the shielding, it's not a big deal.

I prefer modern resistors. Carbon comp resistors only benefit the tone in a couple places, and whether or not it has any perceivable effect is up for debate. I use up to 6 carbon comps in a build, that's it.

It's not the voltage that will call you; it's the current. ;) Play safe!

Thanks,
Josh
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Re: The Fullerwell

Postby crgfrench » Fri 02/22/19 5:54 pm

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

Postby crgfrench » Sun 02/24/19 4:15 pm

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

Postby crgfrench » Wed 03/06/19 7:57 pm

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Re: The Fullerwell

Postby crgfrench » Sun 04/21/19 8:07 pm

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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Re: The Fullerwell

Postby Returnsnull » Mon 04/22/19 10:41 pm

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

Postby crgfrench » Tue 04/23/19 12:00 pm

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

Postby crgfrench » Wed 04/24/19 12:59 pm

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

Postby crgfrench » Sat 05/18/19 12:03 am

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

Postby JMPGuitars » 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.
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Re: The Fullerwell

Postby crgfrench » Sat 05/18/19 6:26 am

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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