Triode TW - Express Kit Build

[Paultergeist]

I guess an easy way to convince oneself IF the chassis is actually part of the circuit would be to lift the PT Center-Tap.....or the cathode grounding.....or the input-jack ground reference.....

Although, I do agree that I think it would be pretty difficult for most humans to detect any sort of sonic difference between chassis metals (all other things being equal).

[xtian]

You're correct, Paul. It depends on the grounding scheme. If you have multiple ground points to the chassis, the chassis itself is tying them together, and then it is part of the circuit.

[John_P_WI]

Again, what does the chassis have to do with slew rate in a properly designed circuit?

[RCGPNY1]

Again, what does the chassis have to do with slew rate in a properly designed circuit?

NOTHING

[RCGPNY1]

IMHO there is always a tendancy for over diefication of someone who's work we like. Now aside from his other accomplishments Mr. Fisher designed 3 amps. Fred Taccone of Divided by 13 has many more designs under his belt. Yes the are derivative..but so are K.F.'s...we dont have to believe or agree with everything he said. The slew rate argument is a prime example. (Geez...I know I'm gonna get it for this one)

[rdjones]

You're correct, Paul. It depends on the grounding scheme. If you have multiple ground points to the chassis, the chassis itself is tying them together, and then it is part of the circuit.

In my understanding of grounding design philosophy, no current AC or DC flows though the chassis.
This can be accomplished several ways, ie star, or by tying various ground points together by wire not the chassis.

The chassis is grounded because it is a shield around the whole circuit.

Does current flow through the chassis on a TW ?

rd

[stevlech]

Mr. Fischer himself admitted some of the lore about him was marketing BS. I'm tempted to think that the red wire is best claim is one of these.

[Paultergeist]

In my understanding of grounding design philosophy, no current AC or DC flows though the chassis.
This can be accomplished several ways, ie star, or by tying various ground points together by wire not the chassis.

The chassis is grounded because it is a shield around the whole circuit.

Unfortunately, the term "grounding" means multiple things in the field of electrical appliances:

1. There is the earth ground -- the green wire from the three wires supplying AC from the wall outlet (in the U.S.). THAT "grounding wire" is NOT normally conducting current, but rather provides an additional path for electrical current to return from to neutral (earth grounded) in the event of a *hot* wire coming loose inside the chassis. In this way, the human does not accidentally become a path for current to flow to ground.

2. THEN there is "ground" perhaps easily understood with automobiles. Look under the hood of a car -- the negative battery terminal is typically connected to the chassis. There are all sorts of electrical devices on that car that are only serviced by a positive-carrying wire -- the other half of the circuit is provided (in this scenario) by making contact with the steel chassis (connected to the battery neutral).

The automotove scenario is similar with most tube amps I have seen. The only way I can see getting away from it is to use a single-point star ground system -- or simply connect all the ground paths together (elevated from the chassis) and have them eventually join up at the CT of the PT.

I am new to the Trainwreck-style of amps, being only involved in my first build of this type, but every layout of a Trainwreck I have ever seen used chassis grounds -- and by "grounds," I mean current-carrying paths through the chassis.

[Paultergeist]

Does current flow through the chassis on a TW ?
rd

Look at the Rocket layout in the Trainwreck files of this site. I count (4) chassis grounds:

1. Pre-amp buss bar (pots, etc)

2. Power tubes cathode resistor and by-pass cap.

3. Power supply filter caps (grounded at rectifier socket mounting bolt).

4. PT Center-Taps (both 6.3V heaters and HT).

(This also assumes the input and output jacks are somehow making chassis ground contact).

Lift any one of those 4 above-noted chassis grounds, and the amp will not function.
Again, it has been my experience that a big part of the confusion stems from MULTIPLE MEANINGS of the term "grounded."

[2tone]

[agreed.. If the ground isn't part of the circuit, then there must be some new laws of electronics being laid out!!




quote="Paultergeist"]

The chassis is not part of the circuit. Should not be part of the circuit.

Not to foster any sort of argument, but this (above) statement contradicts everything I think I know about tube amplifers.[/quote]

[Bob S]

If the chassis isn't part of the puzzle, it wouldn't matter where you tie the negative side of each supply node.
Good luck with that.

[rdjones]

Plenty of amp designs use the chassis as a return for various supply voltages.
One example, the Champ, has the filaments returned through the chassis.
The first change I normally hear suggested when someone mods a Champ is to 'float' or balance the filament supply to eliminate the filament current passing through the chassis.

I suspect in a high gain circuit like the Express that having supplies return through the chassis may contribute to the tendency of instability.
However, far be it for me to suggest that KF's design be fiddled with

reddog

[potatofarmer]

Am I the only one who remembers FM radio tuners that used tubes?

Think about it for a second.

If pentodes and whatnot can be used for MHz-range frequencies (in a steel chassis, I might add) why on earth would anyone worry about their performance at the measly guitar range of 80-6k Hz?

[Zippy]

Al has a better slew rate is supposedly one big reason. I believe this was Ken's thinking..

I've heard Derek Ferwerda talk about "Slew Rate" a lot concerning the EL84 tubes. That was something that supposedly Ken really liked about the EL84 tubes. It sorta made sense at the time but I've lost part of the meaning since then. IIRC it has something to do with how fast a tube responds... don't take that comment as anything significant since I don't recall much about it anymore. Can you you tell us what slew rate is and why it matters?

Slew rate - rate of voltage rise, ie Volts per unit time. Usually measured by inputting a square wave, and measuring the rise time.

[Zippy]

<grrrrrrr - getting tired of debug mode error messages...>