Metropoulos Forum

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:


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)

Closer look at points 4 & 5:
#4 - Bias ground has been attached (Screens filter ground to be added)
#5 - Mains filter ground.

Which transformers are you using?

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?

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

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Here is the ground board with adjustments to wiring:

Progess so far:

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vh junky, looks good!
Mark

Thanks Mark!

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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.

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)?