Question about Filter Cap Grounds for Fender Super Reverb

[coreysan]

I'm building a nice Super Reverb Kit, and I've read that Gerald Weber really likes the idea of keeping the power tube screen supply ground away from the preamp and PI grounds. In the actual assembly (layout), all filter caps share the same wire for ground, but Gerald says to disconnect the screen supply ground from the preamp and PI ground.

If that's a good idea, then the totem pole filter caps can have their own ground, and the preamps and PI can all share a different wire for ground.

Do you think Gerald's suggestion is really important to do, or is this gonna make much of a difference?

[HotBluePlates]

In a stock Super Reverb, the screen filter cap is the one after the totem pole caps, which connects to a 1kΩ resistor but no other resistor. The totem pole caps are for the output tube plate node.

In a perfect world, the totem pole caps and the screen cap have ground wires that connect directly to the same spot as the power transformer high voltage winding center-tap. And ideally, the preamp section filter cap grounds connect directly to the same point as where the preamp stages connect to ground.

I used to own a '67 Super Reverb. All filter caps grounded through the same wire to a spot on the chassis which was close to, but not exactly the same as, where the PT center-tap and heater winding center-tap were soldered to the chassis. There was no obvious hum in that amp.

[coreysan]

Gotcha. Thanks very much. I ask because I'm wondering if I want to make the effort to separate the grounds.
Some builders have said the effort is not required, and as you said, in an amp like this, it most likely will not
generate hum.

But if separating them is a best practice, do you think that doing it Gerald's way is a "guarantee" that at least
that part of the amp won't generate hum?

I'm a first time builder, so I'm nervous about all the little surprises that will pop up when I power up for the
first time. Will this reduce my anxiety level?

[Ed_Chambley]

Gotcha. Thanks very much. I ask because I'm wondering if I want to make the effort to separate the grounds.
Some builders have said the effort is not required, and as you said, in an amp like this, it most likely will not
generate hum.

But if separating them is a best practice, do you think that doing it Gerald's way is a "guarantee" that at least
that part of the amp won't generate hum?

I'm a first time builder, so I'm nervous about all the little surprises that will pop up when I power up for the
first time. Will this reduce my anxiety level?

I would simply ground at the same place as the CT on a Transformer Bolt.  No need to have anxiety.  If you run into problems you can work them out.

No, it cannot "guarantee" because grounds are not the only thing that can generate hum.  I do not use a Dog House for filter caps, I put them inside closer to their location.

I guess Fender has been doing it wrong

Just take your time and build it as the layout suggested for your kit.  Super Reverbs are not generally noisy.  Low gain and all.  My favorite amp, but just too big for most places these days, but man those 4/10's sure do shimmer.

[HotBluePlates]

I ask because I'm wondering if I want to make the effort to separate the grounds. ... But if separating them is a best practice, do you think that doing it Gerald's way is a "guarantee" that at least
that part of the amp won't generate hum?

My personal opinion is folks blame for hum issues on grounding methods and supposed ground loops much more often than those issues cause actual hum. Ed already said it, there are many things that cause hum.

I also agree with Ed that if you follow your kit's directions (or lacking directions, use large clear photos of the inside of a Super Reverb, along with lots of questions here), you will end up with a fine sounding amp without major issues.

The real challenge in your situation is partly the need for more experience (what to believe/incorporate, what to ignore), but also the fact that the likely Fender-style layout is going to dictate the most feasible approach to wiring. If you're building everything from scratch and have some control over layout, it would make changes easier to incorporate from the start. But having done that myself, it's a lot of work (I spent nearly a year overall on a single amp build, from researching the circuit, working through mechanical/circuit layout issues in a computer program, through to actual construction). Experience also helps you recognize how some of the "best practices" are/are not incorporated in existing amps, where they might actually be needed, and how best to implement them.

In itself, a Super Reverb is a big build, and plenty challenging for a first build. I'd advise against "improving" it at this stage.
Disclaimer: Plenty of personal opinion to follow

Gerald Weber is a very personable guy; I briefly met him once. I also started out with some of his books as the basis of my amp knowledge. That said, having learned a lot more about electronics, read the old tube books from the 30's-60's, and having a number of builds under my belt, I see him as a salesman first. He has a tendency to sacrifice broad scope and communication of the relative impact of circuit changes in favor of simplicity/readability. I think he hypes/sells everything, so it might seem to the reader that you can't have "TONE!" without some circuit or construction change.

In reality, there are usually many ways to accomplish a desired result, and many ways to build a functioning circuit. There are also many competing constraints involved in turning a circuit on paper into physical being. And so a lot of times there is one way to do things which works 90% of the time, but will be the best comprise among competing factors in a specific situation. Such is the case with "best grounding method" or "best layout method" or "best wire routing method."

Also, Weber is good at helping a beginner get a grasp of what's happening, but the his books I read up to ~2000 lacked some sound fundamental electronics information. It's not exactly a knock on him; he was writing to a largely non-tech guitarist audience who wanted to "mod their amps." But once you have some tech knowledge under your belt, there are many wider possibilities out there.

[coreysan]

HotBluePlates: you seem to be reading my mind! I started about 9 months ago, and I've been reading everything I can, including books by Weber,
forums, emailing other builders, and contacting repair shops.

After reading a lot on grounding loops, I thought, why not just put the kit together the way the schematic/layout says to, and not worry so much!

I agree about Weber - it makes sense what you said because I wondered about those things in the back of my mind.

So I'll move forward and just follow the "script!" I'm getting excited. I'll be a proud father soon!

I can't tell you how much I appreciated what you and Ed threw in. Thanks a mil!

Corey
P.S. The Reason I'm building this is because back in 1979 I opened a show at NAMM for Larry Carlton, and guess what he did that caused the audience
to give him a standing ovation? All he did was take his ES335 and face it towards a tube amp (Fender Twin I think), and play a high G on the 15th
fret, and create controlled feedback for 3 minutes. So simple, so elementary, and yet, the audience went nuts. He got more cheers than Les Paul did that night!

So here's to tube amps! I love them!

[Mike_J]

One thing I have noticed is there are many ways to make a quiet amp.  I prefer to separate the preamp and PI from the HT and screen supply.  I run a 14 gauge bare copper wire along the pots and tie it to all the ground points on each pot.  I go a little extreme and lift the grounds on the jacks and also run the jack grounds to the same wire. 

I try to segregate the grounds for each power cap in the preamp to the grounds in the section of the preamp effected by that cap.  I then tie a wire from the cap for each section to a spot on the bare wire corresponding to the appropriate pot ground for that section.  The bare wire is tied to ground in only one place and that is near the input jack because I have heard it is the quietest place in the amp and you are less likely to pick up noise in the preamp if you ground it there.  It seems to work pretty well for me so I stick with it.

The HT and screen cap grounds I run together and send to a lug between the ac input and the PT, probably a little closer to the PT bolt.

As was mentioned earlier I would do what the kit is telling you to do but if you have problems the method I just mentioned works well for me.

Thanks
Mike