I finished MaryBeth tonight. I re-wired the entire ground path. Even though she was relatively quiet I thought I might be able to improve on the hum a little. The hum is now well below the hiss even at full volume.
See pictures.
Your comments are welcome.
Steve
MaryBeth is finished!
Moderators: pompeiisneaks, Colossal
MaryBeth is finished!
You do not have the required permissions to view the files attached to this post.
Re: MaryBeth is finished!
Very nice! What did you do differently with the re-grounding?
Tempus edax rerum
Re: MaryBeth is finished!
I'll have to report you Sir, for exposing your child in this indecente manner! 
Any reports on that power scaling?
Any reports on that power scaling?Re: MaryBeth is finished!
Nice! Just a couple minor comments...
Seal those radial filter caps to each other and to the board with some silicone. Those are heavy enough that they'll bend the leads a little every time the amp is moved and they'll eventually break.
Are the white wire tie wrap things rated for high temp? I suspect the heat inside the chassis will eventually destroy the adhesive and those will come loose. There's a lot of heat inside a wreck chassis because of the 1K resistor in the B+ path. If you're not sure, maybe seal them all to the chassis with a bead of silicone around each one.
By the way, I use Elmer's Stix-All Hi-tech Adhesive. It's silicone in small tubes, so you use them up quick. The large tubes all seem to go bad and most of it gets thrown out instead of used.
Seal those radial filter caps to each other and to the board with some silicone. Those are heavy enough that they'll bend the leads a little every time the amp is moved and they'll eventually break.
Are the white wire tie wrap things rated for high temp? I suspect the heat inside the chassis will eventually destroy the adhesive and those will come loose. There's a lot of heat inside a wreck chassis because of the 1K resistor in the B+ path. If you're not sure, maybe seal them all to the chassis with a bead of silicone around each one.
By the way, I use Elmer's Stix-All Hi-tech Adhesive. It's silicone in small tubes, so you use them up quick. The large tubes all seem to go bad and most of it gets thrown out instead of used.
All of your comments...
Regarding the re-grounding:
First of all. All pots and jacks are isolated from the chassis. I found these great fiber shoulder washers at McMaster-Carr. P/N 93920A170. They work perfectly for the switchcraft input jacks (which I prefer for durability over the plastic type) and PEC/CTS type pots. I use the shoulder washer on one side and a flat fiber washer on the other side to isolate the components from the chassis.
2nd. I created groups of mini star ground points. Each star is tied together with a "buss". This buss eventually leads back to a single point on the chassis. (Not the same point as the safety ground). Notice in the first picture I posted that the "star" ground is a star of wires. Now it simply has the one wire from the main filter cap and the center tap from the heater supply. It would be difficult to describe the whole scheme, but suffice to say that the grounds in each section of the amp are tied together in a mini star along with that section's filter capacitor. The buss then becomes a chain of the mini stars starting with the input section and leading all the way back to the primary 40 uF filter cap.
Regarding the power scaling... Still tweaking the amp. Russo and I have discovered some issues that I'm trying to resolve, but the power scaling does work. How well has yet to be determined in a gig atmosphere. Another guitarist friend came over and with his rig we noticed a bit of a buzz the more we engaged the power scaling. "As if the distortion was more solid state than tube driven." More on that later...
We've experienced some serious microphonics coming from V1. Gonna spend some time swapping tubes this week to try to solve this problem.
Paul, Thanks for the advice. For some reason this amp runs relatively cool. I'm not sure what that means... considering all that I've read in this forum because it plays plenty loud, goes from very clean to very dirty.
The large Atom Spragues are resting on the boards so I'm too worried about them. The smaller radials beside them are suspended but they're so small I'm sure they need to be re-inforced with silicone.
-Steve
First of all. All pots and jacks are isolated from the chassis. I found these great fiber shoulder washers at McMaster-Carr. P/N 93920A170. They work perfectly for the switchcraft input jacks (which I prefer for durability over the plastic type) and PEC/CTS type pots. I use the shoulder washer on one side and a flat fiber washer on the other side to isolate the components from the chassis.
2nd. I created groups of mini star ground points. Each star is tied together with a "buss". This buss eventually leads back to a single point on the chassis. (Not the same point as the safety ground). Notice in the first picture I posted that the "star" ground is a star of wires. Now it simply has the one wire from the main filter cap and the center tap from the heater supply. It would be difficult to describe the whole scheme, but suffice to say that the grounds in each section of the amp are tied together in a mini star along with that section's filter capacitor. The buss then becomes a chain of the mini stars starting with the input section and leading all the way back to the primary 40 uF filter cap.
Regarding the power scaling... Still tweaking the amp. Russo and I have discovered some issues that I'm trying to resolve, but the power scaling does work. How well has yet to be determined in a gig atmosphere. Another guitarist friend came over and with his rig we noticed a bit of a buzz the more we engaged the power scaling. "As if the distortion was more solid state than tube driven." More on that later...
We've experienced some serious microphonics coming from V1. Gonna spend some time swapping tubes this week to try to solve this problem.
Paul, Thanks for the advice. For some reason this amp runs relatively cool. I'm not sure what that means... considering all that I've read in this forum because it plays plenty loud, goes from very clean to very dirty.
The large Atom Spragues are resting on the boards so I'm too worried about them. The smaller radials beside them are suspended but they're so small I'm sure they need to be re-inforced with silicone.
-Steve