How important is layout to the TW tone?

[Bob-I]

Gotta comment on the heater issue.

Twisted is common, flying or on the chassis are common also. I've taken to running parallel bus bars, one on each side of the tubes. This is used by Soldano and I copied from him on my SLO Clone. It's quiet as any amp I've ever used and saved a ton of work.

Take a look at this pic, heaters installed on the 9 pin sockets.

[Fischerman]

Bob,
Is that just regular 6.3vac...with either a grounded center-tap or two 100 ohm resistors for a virtual CT? Or did you lift the ground of the center tap to some low-ish DC voltage? I have amp that has heaters like that but the center tap is at 40vdc or so (there is an extra node in the PS rail just for the heater CT). It's actually the highest gain amp I have and is very quiet as well. I grounded the heater CT in my Express clone to ~40vdc when I first built it so I don't know if that knocked down the noise or not.

[paulruby]

Gotta comment on the heater issue.

Twisted is common, flying or on the chassis are common also. I've taken to running parallel bus bars, one on each side of the tubes. This is used by Soldano and I copied from him on my SLO Clone. It's quiet as any amp I've ever used and saved a ton of work.

Take a look at this pic, heaters installed on the 9 pin sockets.

I've done heaters all these different ways and have never had a problem, even in high gain amps. The buss bar method like this works well because all the signal wires still come in perpendicular to the 6.3VAC lines. The only time you get hum from a filament line is if a sensitive node (like a grid line) is running parallel and close to the filament line. Twisted and against the chassis essentially guarantees no signal is parallel and close. So that is why it is recommended. Other methods will work fine but just need to be a bit careful. And, DC filaments is never needed, in any amp. (That comment is bound to get a flame or two.) DC filaments, especially for the inexperienced builder, always causes more issues than it solves (which is none).

[Bob-I]

Bob,
Is that just regular 6.3vac...with either a grounded center-tap or two 100 ohm resistors for a virtual CT? Or did you lift the ground of the center tap to some low-ish DC voltage? I have amp that has heaters like that but the center tap is at 40vdc or so (there is an extra node in the PS rail just for the heater CT). It's actually the highest gain amp I have and is very quiet as well. I grounded the heater CT in my Express clone to ~40vdc when I first built it so I don't know if that knocked down the noise or not.

Just regular 6.3VAC with a virtual CT. I was prepared to raise it up using the switching supply rail, but it's so quiet with just the 2-100R's that I left well enough alone.

[mhuss]

I moved the secondary CT and wrapped the three secondary wires tightly together:
http://mhuss.com/builds/PSimproved.jpg

It made it a bit quieter. Every bit helps!

--mark

[skyboltone]

I didn't even think about that Dan...I think I just saw a Fender chassis and...the heater wires went up in the air. In my Marshall and Express builds I put them against the chassis.

Well I looked at Paul's build and thought I saw his filaments up in the air. That's the way HAD did it. KF runs them twisted down on the deck. I's wrong though, he's got them down.

[skyboltone]

Gotta comment on the heater issue.

Twisted is common, flying or on the chassis are common also. I've taken to running parallel bus bars, one on each side of the tubes. This is used by Soldano and I copied from him on my SLO Clone. It's quiet as any amp I've ever used and saved a ton of work.

Take a look at this pic, heaters installed on the 9 pin sockets.

Man you gotta like that. I hate fussing with flying heater wires. I like to get them in first and down. I'll give this buss bar business a try.

[benoit]

So that's just exposed bus wire? Seems like it would be trouble when you go to measure voltages. Today I was taking measurements on my bassman 20 just for curiosity's sake and accidentally slipped and shorted plate to grid. It was beautiful, and scary, and I shut the amp down right away.. but it was so beautiful. Anyhow the amp still sounds like it did before (not amazing but ok clean). It's getting gutted and wrecked when I get the cash.

[paulruby]

I moved the secondary CT and wrapped the three secondary wires tightly together:
http://mhuss.com/builds/PSimproved.jpg

It made it a bit quieter. Every bit helps!

--mark

I really thought this would kill it off completely. The last thing I can suggest is a shielded line from volume pot wiper to tube grid. That is also a sensitive node and I shield it in mine...

[Bob-I]

So that's just exposed bus wire? Seems like it would be trouble when you go to measure voltages.

It can be, but I typically measure voltages on the board, not the tube socket, unless there's no other choice. My big clumsy hands get in the way.

Another important point on this type of heater wiring is that all other wire need to cross at 90 degrees. I accomplished this by raising the main board on standoffs and arcing the wires downward.

[benoit]

It can be, but I typically measure voltages on the board, not the tube socket, unless there's no other choice. My big clumsy hands get in the way.

That makes sense, I should have thought of that. Thanks.

[mhuss]

I really thought this would kill it off completely. The last thing I can suggest is a shielded line from volume pot wiper to tube grid. That is also a sensitive node and I shield it in mine...

I've never worked on an amp so noise-sensitive (even high gain ones) -- just getting your hand near the input end (e.g., to measure a voltage) causes the hum to noticeably increase. I don't think a bottom chassis plate is optional on this one! Perhaps it's that oddball high impedance tone stack...

--mark

[marino]

In all layouts of wrecks and liverpools I've seen there is a common positioning of filter caps, alltogether located near power transformer. I wonder is it possible to get acceptably low hum level with typical bus grounding scheme with filter caps located in the area where they actually do their job in schematic, for instance, first preamp stage elements with associated filter cap nearby and so on. Just like many proven layouts of marshall 18 versions. By the way, I will be making 2xEL84 liverpool and I did in the past bus groundings with ok results according to Aiken amps tips. Could it be that really high gain amp demands filter cap locations as in wreck layouts?

Thanks!

Marin