Busbar earthing.

We all start somewhere
Post Reply
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#1 Busbar earthing.

Post by pre65 »

Can some kind soul explain the principle of busbar earthing for me, in particular where each component should go in relation to the others ? :?
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#2 Re: Busbar earthing.

Post by Cressy Snr »

pre65 wrote:Can some kind soul explain the principle of busbar earthing for me, in particular where each component should go in relation to the others ? :?
OK.... The principle is that the components with the heaviest current draw go closest to the point where the busbar itself connects to the chassis ground point.

So what you do is to run a length of bare copper wire of at least 1mm diameter from the chassis ground point where the mains earth connects, right to the other end of the chassis, where it connects to the input socket grounds.
The socket grounds must of course only connect to earth via the busbar. If the outers of any of the input sockets are in contact with the chassis metalwork, you will get an horrendous earth loop.

Once this wire is run, and the socket earths are in, next come the input valves grid resistors, then the cathode resistors then the bypass caps.

Next, the driver stages, grid resistors, cathode resistors, bypass caps.

Next, we have the output valves grid resistors, cathode resistors and bypass caps.

We have now reached the PSU end of the busbar and are close to the ground point, so all we have left are the PSU caps. These grounds come next. along with any HT rectifier centre taps. Last of all, the heater centre taps.....job done.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
User avatar
Greg
Social outcast
Posts: 3198
Joined: Wed May 23, 2007 11:14 am
Location: Bristol, UK

#3

Post by Greg »

Steve, thank you for your clarity and most helpful reply to Philip. Whilst I'm not needing this info at the moment, your post is excellent and I've saved it for future reference.
User avatar
pre65
Amstrad Tower of Power
Posts: 21373
Joined: Wed Aug 22, 2007 11:13 pm
Location: North Essex/Suffolk border.

#4

Post by pre65 »

Thanks Steve.

Would the volume pot grounds go to the quiet end as well ?

And also the shield/screen wire from the mains transformer ?
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
Cressy Snr
Amstrad Tower of Power
Posts: 10552
Joined: Wed May 30, 2007 12:25 am
Location: South Yorks.

#5

Post by Cressy Snr »

pre65 wrote:Thanks Steve.

Would the volume pot grounds go to the quiet end as well ?

And also the shield/screen wire from the mains transformer ?
Volume pot grounds at the input socket end before the input valve grid resistors.
Screen wire from the mains transformer, at the mains earth end
with the heater centre taps.

The whole principle of bus bars was known in old fashioned parlance as "earth follows signal"

If you look at how I have described bus bar earthing, you will see that earth busbar does indeed follow the signal, through from input to output. From there, it disappears into the power supply and finally into the earth itself via the mains cable.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
David
User
Posts: 123
Joined: Wed Jan 05, 2011 3:12 pm

#6

Post by David »

Hi, on my 300b clone I connected the mains tx screen to chassis earth rather than the earth bus bar as the earth bar is raised and that seems a much safer option. Are you saying I should have connected this to earth?
Thanks
David
User avatar
Mike H
Amstrad Tower of Power
Posts: 20157
Joined: Sat Oct 04, 2008 5:38 pm
Location: The Fens
Contact:

#7

Post by Mike H »

No TX (electrostatic screen) always goes to mains earth (chassis). Because this is a required safety feature, it separates the mains from the secondaries with a mains earthed screen.

EDIT: your busbar is amplifier earth, that can be raised with an earth lift resistor OK.

What Steve said.

The basic premise is to avoid high currents, e.g. output stage(s), going through the earthing for more sensitive stages, e.g. input(s).

This logically translates into the 'herring bone' arrangement, PSU & outputs at one end & inputs at 'tother end. Intermediate stages in between.

HTH ?
 
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
Post Reply