lead dressing

[sniffyduke]

hi all,

I have a question. I have been looking at alot of inside pics of alot off different amps.

I specifically have been paying attention to the dressing of the BLk
and Red heater wires. that go to the tubes.

I recently built a Dumble clone and made sure the blk and red lead wires were tucked against the back wall. I was in belief that tis eliminates noice ect. But to be honest I really have no clue on that subject.

When I looked at pics inside of real Dumbles and various Trainwrecks
I notice this isn't the case.

In the pics of Larry Carlton's Dumble, I notice the dressing is directly over the tubes.

On V1 and V2 I also noticed that the cathode, is moved far away from heater wire except on PI.

Can some one explain to me the reasons for tucking your heater wires against back and placing them close or over tube sockets.

Is there a reason for these methods.

Thank you

[Andy Le Blanc]

Its several examples of how to minimize hum interference. The fil. dress,
or heater wiring carries a high current ac voltage that can "leak" into the
signal path. The dress is twisted to minimize this. Placement can be a real
bugger in high gain pre's, proximity to the chassis helps. "Chop sticking", or
using a non-conductive probe to move wires around is one way to reveal
problem areas. All of the variations you see are valid, its a compromise
between noise performance and the investment of time it takes to dress the amp.
The over the sockets dress is a fender thing, I've seen more tube based
pieces with the heaters wires twisted and flat on the chassis or in a corner.

[sniffyduke]

thanks,

I thought it might have somthing to do with sustain.

i have seen dumble clones with wires twisted and against back wall.
When i saw the inside of a real dumble it has the heaters over tubes.

is there an advantage to placing heaters directly over tubes vs against back wall?

So, hi gain amps its a good idea to place heater dressing against wall
but in clean fender style over tubes is prefered?

thanks, i'm still learning.

but Trainwreck express i notice heaters close to tubes.
but isn't that a high gain amp?

[Andy Le Blanc]

Fender is a successful long running product that has been used as a clone
base for decades. Everybody rips fenders, they're easy assembly with
cheap factory labor. Its more the style you emulate then anything.
DC heaters are much quieter with enough filtering, where its advantageous.
Keep checking out layouts and build styles there's many ways to do it.
Lots of ideas to explore

[Phil_S]

Andy gives a solid explanation here. I'd add that placement of the heater wires is probably best determined by the person who is building, based on the particular layout in the chassis, the builder's skills and experience, and the kind of wire being used.

I find the Fender style over the tubes to be both effective and easy to implement. That's a good reason for me to do it that way. The concept at work here, as Andy points out, is to keep the high current filament wires away from the signal wires. By placing the heater wires in the air, you can put the signal wires down on the chassis floor. This makes for good separation and it is what makes any system effective.

You could easily put the heater wires on the floor and signal wires in the air, too and achieve the same separation. I've seen examples of this. I think it's messy, though, and in amp construction, I believe neatness counts.

Besides tucking the heater wires into the corner, also an effective way to isolate that string of wire, I've seen pictures of amps built with zip cord for the heaters. (zip cord = lamp cord, the stuff you find on a lamp with a plug at the end ) The perfect parallel nature of zip cord eliminates the need to twist and does the same thing for hum cancellation as the twist.

A final comment on the twist. It needs to be tight and neat. I hope that I'm within the fair use clause of the copyright law. See the attached picture. Click to enlarge. Note to moderators, please do the appropriate thing here...I'm not looking for trouble.

[Bill Moore]

I can't get the pic to post of the 94 Twin chassis I had, but the power tube heater wires were a twisted pair next to the chassis, approx 1 1/2" away from the socket. The wires are 90 deg to the sockets. The preamp tube heater wires lay on the chassis, and follow a sinious pattern between the sockets, never touching.
I used that scheme on my AB763 Twin clone, and ran the signal wires into the top of the socket. I hope to find out if it works this week.

[sniffyduke]

Wow, thanks for the tips guy's.
That helps alot.

Another question:

I notice on dumble amps that most are powder coated. (black)
Is there a reason for this or is it just for looks.

I assume his chassis were aluminum.

[Andy Le Blanc]

You are in a consumer market, if its cheap and gets a sale, it becomes a market trend.
Think about it, the only reason to use aluminum is for its conductivity.
But other than that its a band aid for poor design, but if kit assemblers and
cloner's will spend $$$ because they think its makes for a better tone, or if
they think it will make they're build more authentic, there's a niche for
market exploitation.

All consumer product is as crap as you can imagine.

Bent steel, plywood, contact paper and spray paint. NO JOKE.....

The good old days were never as good as anybody remembers them as.

I would very much like to go the other way of course, we all do.
Think of the cab and chassis as a presentation, your making a visual offering.
What offering would you make? What aesthetic would you use?

[Structo]

I don't think the only reason for using aluminum is conductivity.

A couple other reasons have to be, soft-easy to work with.
Light weight, we don't need to tack on a couple extra pounds to the transformers.

I suppose it may conduct electricity better than steel but you don't get the electromagnetic shielding like you do with steel.

Powder coating is a great finish because it is very durable.
Much more durable than regular spray paint.
Then add some classy silk screened graphics and you have a killer looking chassis.

Never was fond of silverface anything, not guitar amps and not stereo gear.

[Andy Le Blanc]

Part and parcel to the history of tube electronics is the ability to do home assembly.
The parts you cant make easily at home, tubes, caps, resistors and transformers,
are still relatively abundant and cheap. Its in the garage or basement where
new products are still created.

Every step of the way you have to ask your self what you can do at home with what you got.

Can you power coat at home with locally found materials?
I can see fab-in a silk screen machine if your going to make a large enough run.

I can see a wood shop, metals station, all the steps of a fabrication process.
But the heart of it is home based. The less you have to source and purchase
out of house the better.

Aluminum is costly, steel is right down the road at the local tin knocker,
and it says "MADE in USA" on it.

Now one thing that I haven't seen addressed is the type of coating on
older chassis. You can solder to it. Its "tinned".
Is it plated? Is it a dip? What is its trade name?

[Phil_S]

Can you power coat at home with locally found materials?

Sears makes a consumer level powder coating kit, at a reasonable price, as I recall. Just about any color you want and perfect for a one-off chassis. I don't know if it will qualify for your definition of "local."

[Andy Le Blanc]

There's a sears in Bangor, Augusta, but its a two hour drive and I refuse to use a credit card.

I had a remembrance and found this..... a bit more to the keeping of the post.
On the second page there are specific suggestions for the hand builder
pertaining to heater wiring and the order in which construction should proceed.
Its from the 1937 radio amateurs handbook.