Why we don't go with floating B+

[kagliostro]

There is a particular reason for which we don't go with floating B+ on amps and we ground the negative somewhere ?

 

Thanks

Kagliostro

[sluckey]

Yes. It's convenient to use the metal chassis as a conductor just like in the auto industry. Lot's cheaper too.

[RicharD]

+ it's always good to have a 0V reference, otherwise heater to cathode voltages could get away from you.  Oh yeah, you want your input shield to be 0V.  That could get sticky if your shield was 100V and your B+ was whatever above that.  Grounding is a good thang.

[PRR]

> floating B+ on amps and we ground the negative

? ? ?

There has to be a complete loop, B+ through tube to B- and return via battery (or power supply).

System connection is FAR simpler if power and signal for all stages are common.

But you can have a battery for every stage, transformers between stages, and have totally separate power, signal, and frame/shield "grounds". Some older telephone and recording gear was built this way.

[kagliostro]

Thanks to ALL for explanation

Grounding is a good thang

I was thinking that with the "new" 3 conductors cord having the connection of the chassis to ground the amp user was still protected against "failures" and using a floating B+ will prevent, in some way, hum or other noise avoiding loops

obviously I was wrong, if that were true many people have already done

Kagliostro

[TIMBO]

Thanks Kagliostro for asking that great question because it got me thinking about my TOS build. I have had trouble with another builds (hi gain)so i had a reread of merlins grounding. It says that there should be only TWO connections to the metal chassis, one being the earth connection( the green/yellow wire of the three prong power cord that protects the user) and the second the amps circuit ground and yet to make a electrical circuit you must have a + and a neutral but the amps circuit is not connected to the neutral  its connected to mother earth  So why don't we connect the amps circuit to the neutral. Thanks

[kagliostro]

I think that the connection to neutral is not so practical

only in few countries (as far as I know) has a way of insertion for the wall plug

as example, here in Italy, I can revert the plug and so revert the neutral connection to the circuit

----

indeed we connect the PT to phase and neutral and we are glad to have the PT acting as a galvanic isolator for the circuit, on the wall wart there is a relatively low voltage (here 220v AC voltage) but a VERY BIG CURRENT disposable and that current is Higly dangerous

Kagliostro

[RicharD]

Utility talk here.....  The neutral (white) wire is grounded at the secondary of the utility transformer and again at your house.  It is the intended current flow path back to earth.  The green wire is for short circuit protection. 

[jcm-jmp]

hi guys,

the nuetral is also connected to ground or mother earth at your service entance to you home or buisness. here in the USA we are governed by the NEC national electrical code which requires a bonding jumper between the neutral buss and the grounding buss in the panel on single and multiple family dwellings. section 250.66 of the NEC requires a bonding conductor from the source panel board or switch gear to the grounded conductor (nuetral) on all transformers in commercial buildings. so, though you may think you are not grounded and your nuetral is floating, in realality your nuetral is bonded to earth ground at the service entrance of your home ,office, or local watering hole. Now you can lose you ground at the wall receptical dew to bad connection or just plain old style receptical that has no ground pin, but even then (grant it it will be noisey) your nuetral conductor is still bonded to earth ground at your panel or high voltage transformer. These transformers are not the transformers in your amp. They are much larger and handle much more current than you amps and are used to drop 480v 3 phase power down to 120v 3 phase power, but the principal is the same.

[kagliostro]

Here (in Italy) there is no connection to ground for the neutral at single home

only green/yellow is connected to ground

may be that connection is in some place at the electricity supplier factory or line structure

some time ago (not very much .....) in my town there were also wall wart with green/yellow earth connection and two phase instead of one phase and one neutral (same 220v), don't know how & why

I'll investigate about it ..........

however my question was about not connect the B- to chassis

The neutral (white) wire is grounded at the secondary of the utility transformer and again at your house.

RicharD I'm not able to follow you

do you mean the white (neutral) wire is connected to the primary of the utility transformer ???

Kagliostro

[PRR]

> may be that connection is in some place at the electricity supplier

[PRR]

Is this your outlet?

Information on the Type C European 2-pin Electrical Adapter Plug and Electrical Outlet

Popularly known as the Europlug, the Type C electrical plug is a two-pin unearthed plug used throughout continental Europe, parts of the Middle East, and much of Africa, South America, central Asia, and the former Soviet republics.

[kagliostro]

Years ago we had those 2 hole outlet

now we have 3 hole outlet, something like this in the attached image

the outlet in the right is a schuko outlet and also if not all outlet are like that it is often used (we call it german outlet)

all house (now) has (or better should have) a pole grounding (old house often still now haven't)

Kagliostro

[PRR]

> Years ago we had those 2 hole outlet

Thanks. The web-page I found said that this was _the_ normal outlet in much of Europe including Italy; I suspected that 3-hole outlets were used in recent construction and repair.

> palina messa a terra.jpg
 
Thanks for the words. I discovered wire-stores in Italy.
 
This 150cm/5-foot copper/steel rod is also used, and is very much like we use on most homes in the USA:
Palina di messa a terra ramata, lunghezza 150cm Prezzo:  € 17,85

The pictures in this thread look a lot like special-case USA wiring:
http://www.arifidenza.it/forum/topic.asp?TOPIC_ID=145857

Some of that is about amateur radio, or radio/TV/data cables, and some may be about lightning protection.

http://it.wikipedia.org/wiki/Messa_a_terra

The goal for palina messa a terra is the same everywhere, though details may be different. The street transformer has a ground on one power wire. The house has a ground. Usually these are connected together at the "house entrance", the meter or the fuse-box.

[kagliostro]

Hi PRR

http://www.arifidenza.it/forum/topic.asp?TOPIC_ID=145857

there there is the description of the ground connection in the house of an italian radio amateur

Some of that is about amateur radio, or radio/TV/data cables, and some may be about lightning protection.

exact, also lightning protection

The goal for palina messa a terra is the same everywhere, though details may be different. The street transformer has a ground on one power wire. The house has a ground. Usually these are connected together at the "house entrance", the meter or the fuse-box.

Yes, here we haven't the neutral connected to the ground pole at home, the connection exist but is somewhere else

I asked about the presence, time ago, in the old town, of outlet with phase + phase instead of phase + neutral

They told me that is the result of an old distribution line

years ago at home we had 125v for illumination and 220v for appliances

than the 125v was put out of service and we have 220v only also for illumination

some lines were converted to 220v by using 2 x 125v lines

or so they told me

Kagliostro

[bigsbybender]

years ago at home we had 125v for illumination and 220v for appliances

than the 125v was put out of service and we have 220v only also for illumination

some lines were converted to 220v by using 2 x 125v lines

That is the way it is done in North America.  2x120v lines are used together to make 240v for large appliances, air conditioners and equipment.  Small appliances (and guitar amps) are 120v however.

now we have 3 hole outlet, something like this in the attached image

I noticed those the last time I was in Italy about 10 years ago, this was in a new building. I lived in Austria at the time and had to purchase some adapters for using my German items in Italy.

j.

[jcm-jmp]

well looks as though europe has come of age and started the use of a grounded electrode and conductor through out the end user systems.

At any rate, as long as there is a conductor that is attached to each appliance chasis (guitar amp, oven, fridge, air conditioner, ect....) at one end and attached to a earthed grounded buss in the panel, which in turn is connected with a large enough conductor to handle the ground fault current of that paticular service at the buss end and is routed to a ground rod (8 foot x 1/2 - 5/8 inch copper coated ground rod in USA) that is completly incased in the earth at the other end. there is a suffiecent means of ground (less than 2 ohms) from the equipment (amplifiers PT's iron core) to earth to keep the B+ rail from floating.

A floating (un-grounded) amplifier is a good way to see how the human body can act as a conductor and become the ground for the unit.

in other words YOU COULD GET ELECTRICUTED AND DIE! without a earthed ground on your high voltage tube amplifier.

[kagliostro]

Hi Jcm-Jmp

A floating (un-grounded) amplifier is a good way to see how the human body can act as a conductor and become the ground for the unit.

I think you misunderstand my original question

I was asking about floating B+ in the amp (in practice don't connecting the B- to the chassis)

The chassis however will be anyway connected to ground via the third connector in the cord (green/yellow wire) that is connected to pole grounding.

Hope now you can understand better my original question

Kagliostro

[jcm-jmp]

oh
so sorry.

 it is a common chasis connection like done in auto's for cost and convienence.

 like PRR stated -- you must have a B- to complete the circuit.

also it gives a 0v ground reference point for saftey.

[PRR]

> I was asking about floating B+ in the amp (in practice don't connecting the B- to the chassis)

Look at the first tube of a guitar amp.

Power is fed plate-cathode.

Signal is fed grid-cathode.

Guitar plug shell (and usually guitar strings) is therefore connected to first tube cathode, and thus to B-.

There "are" other ways.

Guitar signal can be transformer-isolated. However the standard guitar pickup (wound for maximum signal to a grid) is not a good source for a transformer. We "could" wind 200-ohm pickups and use a 200:20K mikcrophone transformer. Les Paul had some guitars like that. It has never been as popular as high-Z winding right to a grid.

You could come into a JFET or chip buffer, signal transformer, then floating B supply amplifier. But how do you power the buffer? Yes, it might only be 12V. But still its PT insulation can fail and put 117V or 230V on the input jack shell.

Look at the Kent amp I posted, or some later KAY amps. The first cathode returns to B- through 100K and 0.05uFd. The idea is, if B- turns out to be 117V "live", there is less than 2mA of current possible in 100K||0.05u, and this is usually "safe". (But cheap caps can short-out.) It also reduces the maximum output of the first stage.

What we want to do is be sure that EVERYTHING we can normally touch is connected together. The outside of the electric stove and the water faucet next to it. The heating radiator in the music room and the face/case/plug of the guitar amp. Historically we have metallic water (and steam) pipes throughout the house which return to cellar and to dirt around the house to the street.

[kagliostro]

Thanks for this further info PRR

Kagliostro