12xxx Larry Ground

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vh junkie
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12xxx Larry Ground

Post by vh junkie » Thu Jan 27, 2011 2:03 pm

Implementing Larry's Ground scheme on a 12xxx.
Here is a partial quote from:
http://forum.metroamp.com/viewtopic.php ... 0&start=18
novosibir wrote: There are some basical rules:
Think your ground points along a line across the chassis.
1-st come the inputs & V1 cathodes
2-nd come volume & V2 grounds
anywhere between 1 & 2 the preamp filter ground
3-th comes tone stack, V3 (presence), PI filter & speaker jack grounds
The OT's secondary common has to be grounded to the speaker jacks !!!
4-th comes the bias & screen filter's ground
5-th comes the rectifier ground (or HT CT), 1-st filter ground & output cathodes
6-th is the earth from the wall supply ONLY

Best (quitest) place for the heater CT would be 1-st ground spot, although a long way there. May put to 4-th, but NEVER 5-th

I've showed the 'ideal' above!
Do it simpler and have the risk of hum!
Larry
Trying to keep the ground points just under the edge of circuit boards for a cleaner look.
Here is the progress so far with points 1 thru 5 labeled:
Image

Trying to keep the ground lugs tucked under the edge of the circuit boards for a cleaner look.
Closer look at points 1-4:
So far:
#1 - Heater common has been attached (Inputs and V1 Cathode to be added)
#2 - (Volume controls and V2 Cathode to be added)
#3 - PI filter ground has been attached (Tone stack, presence grounds, and speaker ground to be added)
#4 - Bias ground has been attached (Screens filter ground to be added)
Image
Closer look at points 4 & 5:
#4 - Bias ground has been attached (Screens filter ground to be added)
#5 - Mains filter ground.
Image
Last edited by vh junkie on Sun Jul 29, 2012 3:13 pm, edited 10 times in total.
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axeman
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Re: 12xxx Larry Ground

Post by axeman » Thu Jan 27, 2011 2:05 pm

Which transformers are you using?

vh junkie
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Re: 12xxx Larry Ground

Post by vh junkie » Thu Jan 27, 2011 2:44 pm

The PT is a Marstran 1203-80
The OT is a ****** 1202-132
In both cases the wire colors are different than the Metro trannies.
Seems to be some discrepancy in which way the OT should be oriented:
George's have the primary on the right:
http://plexireplicas.com/metropoulos-am ... 00-series/
A lot of the builds have the primary on the left though?

Which is right?
Last edited by vh junkie on Wed Feb 16, 2011 6:21 am, edited 3 times in total.
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Re: 12xxx Larry Ground

Post by axeman » Thu Jan 27, 2011 3:07 pm

On the Right. Were did you get the power tube sockets.

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Re: 12xxx Larry Ground

Post by vanhalen5150 » Thu Jan 27, 2011 4:33 pm

.................
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Re: 12xxx Larry Ground

Post by vanhalen5150 » Fri Jan 28, 2011 6:59 am

.............................
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Re: 12xxx Larry Ground

Post by vanhalen5150 » Fri Jan 28, 2011 11:36 am

............................
Last edited by vanhalen5150 on Wed Feb 16, 2011 8:42 am, edited 1 time in total.
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vh junkie
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Re: 12xxx Larry Ground

Post by vh junkie » Fri Jan 28, 2011 3:03 pm

Here is the ground board with adjustments to wiring:
Image
Last edited by vh junkie on Wed Feb 16, 2011 6:28 am, edited 3 times in total.
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Re: 12xxx Larry Ground

Post by vh junkie » Sun Jan 30, 2011 10:05 am

Progess so far:
Image
Last edited by vh junkie on Wed Feb 16, 2011 6:28 am, edited 2 times in total.
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Re: 12xxx Larry Ground

Post by vanhalen5150 » Wed Feb 02, 2011 11:09 am

...........................
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Re: 12xxx Larry Ground

Post by rockstah » Wed Feb 02, 2011 11:14 am

vh junky, looks good!
Mark

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Re: 12xxx Larry Ground

Post by vh junkie » Wed Feb 02, 2011 2:15 pm

Thanks Mark!
Last edited by vh junkie on Wed Feb 16, 2011 6:29 am, edited 2 times in total.
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Re: 12xxx Larry Ground

Post by vanhalen5150 » Mon Feb 07, 2011 9:33 am

..........................
Last edited by vanhalen5150 on Wed Feb 16, 2011 9:15 am, edited 1 time in total.
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Re: 12xxx Larry Ground

Post by Strat78 » Tue Feb 08, 2011 8:17 pm

I love this grounding scheme! Those pictures are a huge help for those of us who need visuals. Ground #6 is to the PI filter lug? Anyway, here is how I ended up working with the existing 68 chassis holes for the 2" core OT wires: I shaved off a little from one of the OT'a feet to allow for the grommet. The OT sits a bit off the chassis anyway, so I mounted it partially over the grommet. Seems OK (a small piece of tape on the OT to prevent the metal from chaffing the wire sheathing), but will having the wires that close to the core cause noise? I'm waiting for some chokes from different manufactures to arrive (3H, 3.6H, 5H and a 7H) before I get started again. :D
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Re: 12xxx Larry Ground

Post by Strat78 » Tue Feb 08, 2011 11:45 pm

Robert, for the OT primary's, you have the red and white going to V5 and V6, should it be the brown and red (that's how it is shown in Georges directions, but perhaps Chris' tranny's are different here)?

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