6G3 rebuild: budget winter break project

[dwinstonwood]

Wanting an inexpensive project to work on over the holidays, I've decided to rebuild my 6G3 Deluxe with some "improvements." This was the second guitar amp I built, and even though it works fine a lot of the lead dress and soldering is sloppy. So, I ordered some parts from Doug.
Here are the changes I'm making:

1.) new turret boards (never liked eyelets) and will use Doug's bias circuit.
2.) adding grid stoppers and screen resistors to the power tubes.
3.) moving the 1 Ohm bias-test resistors onto the board.
4.) removing the external speaker jack and moving the ground switch to that spot as a NFB switch.
5.) redesigning the grounding scheme - trying to follow Doug's method.
6.) upping the filter caps from 16uF/16uF/16uF/8uF to 22uF/22uF/22uF/16uF.
7.) reorganizing some of the on-board wiring, but keeping all of the original component values.

Here's my new layout showing the changes, and the original Fender schematic:

https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_6g3.pdf

[sluckey]

I'll pull up a chair.

[Willabe]

I'll pull up a chair.

Too watch the fireworks?

That layout drawing has some very serious mistakes. 

I'll give you some hints, -bias/B+/grounding. Watch what you tie to what.
Edit; See later reply. 

[sluckey]

Too watch the fireworks? 

That layout drawing has some very serious mistakes. 

I'll give you some hints, -bias/B+/grounding. Watch what you tie to what.

I don't see any fireworks issues. Can you give us a stronger hint?

[Willabe]

I couldn't see the gray holes and gray ground make, I thought they were all wired together, carry on. 

Edit; Spelling

[dwinstonwood]

Willabe, the chassis holes for the wires running to and from the doghouse are definitely not clear in my layout. It does look like the red and black wires are connected. See snippet below - I redrew it.

I'll pull up a chair.

Thanks!

[sluckey]

Now that's a much better grommet.   

[Junior Little]

Wanting an inexpensive project to work on over the holidays, I've decided to rebuild my 6G3 Deluxe with some "improvements." This was the second guitar amp I built, and even though it works fine a lot of the lead dress and soldering is sloppy. So, I ordered some parts from Doug.
Here are the changes I'm making:

1.) new turret boards (never liked eyelets) and will use Doug's bias circuit.
2.) adding grid stoppers and screen resistors to the power tubes.
3.) moving the 1 Ohm bias-test resistors onto the board.
4.) removing the external speaker jack and moving the ground switch to that spot as a NFB switch.
5.) redesigning the grounding scheme - trying to follow Doug's method.
6.) upping the filter caps from 16uF/16uF/16uF/8uF to 22uF/22uF/22uF/16uF.
7.) reorganizing some of the on-board wiring, but keeping all of the original component values.

Here's my new layout showing the changes, and the original Fender schematic:

https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_6g3.pdf

You might want to look at the rectifier wiring...specifically pin 6.

[sluckey]

You might want to look at the rectifier wiring...specifically pin 6.

Yes. And while you're at it... You have B+1 and B+2 jumpered together on the board. That puts the screens on the same node as the plates. There should be a 1K/2W resistor between B+1 and B+2. Probably is on the cap board but that jumper shorts out that resistor.

[dwinstonwood]

Yikes! Great call Junior Little! Thank you. I moved the wire to pin 8. 

sluckey, thank you, too! Yep, there will be a 1K/3W in the doghouse between B+1 and B+2. This part of the circuit brings up another possible mod/improvement: adding a choke. AES sells the Deluxe Reverb 194A choke for $18.50. I'll think on that.

So, the chassis has been gutted. I cleaned up all the pots, jacks and switches. As I said, my original soldering was pretty sloppy; I used half a spool of de-soldering braid cleaning them up. I'm using all new tube sockets.

The next thing I'll do is drill the new boards and install the turrets. I was able to clean up the filter cap board, so I can reuse that.

And, I've attached an updated layout with corrections. Thanks again for spotting errors!!!

[dude]

I love that amp, 6G3 but that .003 cap across the first stage preamp plate R, just made that channel way too dark but just my opinion  . Maybe a different value..? 
Anyway, nothing more enjoyable then to "re-do an amp you build years ago into a master piece". Keep the build posted as you go.
Cheers

[dwinstonwood]

Thanks dude. Honestly, I rarely played my Tele (bridge) through the bright channel. But, a "dark" cap somewhere halfway between the bright and normal channels would be worth experimenting with. 

Turrets installed. My homemade swage tool is a bit fussy, but it works fine once it's set up in the drill press. The one Doug sells looks a lot better.

[dude]

That .003 across the 220k is on the normal channel, that and just the two coupling caps, .022 and .01 are the only differences in the channels. Using a tele, l can see leaving that .003 in the circuit.
Just something about that amp, that just sounds amazing. Fender didn’t usually use 220k plate R’s maybe the extra distortion they bring is the magic..?
Anyway, looks great.

[dwinstonwood]

Heater wiring is done.

I really have no idea why there are so many holes drilled in this chassis.
I guess I had to relocate a lot things with the first build.

[dwinstonwood]

Wiring is done (still need to install the power cord).
In case something looks a bit odd, the power tube sockets are installed 180 degrees different than the Fender layout, so pins 1 are closest to the board.
The bias circuit board turned out nice and compact.
Tomorrow, I'll populate the board.

[southboundsuarez]

Nice! I will be following this,,,
My friend was just inquiring about building a Brownface Deluxe... He just built a Mojotone Tweed. I will have to talk him into looking at Hoffman's board instead of a settling on another Mojotone. He already is very impressed with turret construction vs eyelets.
Thanks for posting your rebuild.
Happy Holidays.
Brian

[dwinstonwood]

Thanks Brian. Yeah, for me the turrets are a lot easier to work with than eyelets.
The parts are installed. Now, it's time to go over everything (more than once) and weed out any goofs.

[sluckey]

Neat and clean!   

[dwinstonwood]

Thanks sluckey! It was a fun rebuild.

So, here's a photo of my original build; I must have thought I needed all those 3W resistors at the time. Messy wiring, and lot of the solder joints were suspect.

I need to measure my negative bias voltage range after an initial dim-bulb test. I'm using the same bias range resistor (10K), and the same PT with a 50V tap, so I should get a range either side of -26V as is, but I'll make sure I do.

[dwinstonwood]

With the 10K/3W bias range resistor I got a sweep of -23.6VDC to -39.8VDC on both #5 pins.

I swapped in a 15K/3W and now my bias range is -19.8VDC to -35.2VDC. I think this is a better range.

[sluckey]

I think you may have shifted the bias sweep range the wrong direction. All three of my 6V6 amps have the voltage on pin 5 adjusted to approximately -36v, -38v, and -38v in order to run at 70% dissipation. I like to set the bias pot to midrange and then experiment with the range resistor to give me -36v. This allows me to adjust lower or higher.

[dwinstonwood]

I think you may have shifted the bias sweep range the wrong direction. All three of my 6V6 amps have the voltage on pin 5 adjusted to approximately -36v, -38v, and -38v in order to run at 70% dissipation. I like to set the bias pot to midrange and then experiment with the range resistor to give me -36v. This allows me to adjust lower or higher.

Yes! You are right, as always, sluckey. The lowest mV reading I could get across the 1 Ohm resistors with the 15K was 23-ish mV's.
I went back to the 10K and now I have one 6V6 at 20.2mV and the other at 19.4mV with the bias pot close to the halfway setting. That's about 60% plate dissipation.

Plate voltages are 377.3VDC and 375.9VDC.

The 10K is the correct bias range resistor for the Hammond 50V bias tap.

[dwinstonwood]

All four inputs work as they should.

Here are the 7025 voltages with the tremolo turned off:
V1: P1 - 172.3
      P6 - 171.3
V2: P1 - 176.2
      P6 - 220.1
V3: P1 - 237.7
      P6 - 229.4

But, the tremolo... It sounds great with very wide ranges of both speed and intensity. Really nice. This is with my cheap test speaker. I'm going to go ahead and put it back in the cabinet and play it through the WGS G12C/S.

This was a totally worthwhile project, and it cost less than $80 in new parts from Doug. But, it was as much fun as building a whole new amp.

Thanks for all the guidance and help y'all! Thanks for pulling up a chair sluckey.

On a side note, I recently bought an Allparts TMNF-FAT Chunky neck with tall/narrow frets for my Tele. It's the most comfortable neck I think I've ever played (I have short fingers, so thin necks are extremely painful). As a result I've been playing a lot more, and now this is almost like having a new amp.

[dwinstonwood]

I've been playing the amp for a while now, and it does sound great. No wonder the 6G3 is so popular - raw and simple, but rich and smooth. Just rudimentary guitar signal amplification. dude, you're probably right about the 220K plate load resistors; that could be what makes it special. This rebuild is so quiet compared to my original build. I'll be sticking with this grounding scheme. I used the Valve Wizard grounding scheme on my 6V6 Plexi w/hot switch and it's totally quiet, too, but for me it was more complicated to wire up.

A mystery to me is why I now have no tremolo thumping. Could it be the extra filtering in the bias circuit? I have a diode across the Intensity pot, but I had one on my original build, too. Something about this rebuild eliminated that issue, but, I don't know what.

Now, I want to hear it with a really good Alnico. Maybe I'll start saving up.