Hammond Power Transformer Earth ground question

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joeyello
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Hammond Power Transformer Earth ground question

Post by joeyello »

I recently installed a Hammond (290PAZ) output transformer in my Marshall 1974X. There are 12 wires on the transformer with no wire for earth (green wire) ground. The original transformer had a green wire that bolted to the chassis.

Do I need to wire the transformer to ground some how? Any help would be appreciated.

I notice the amp hums when my hands are not on the guitar strings……seems like a grounding issue to me.

Thanks
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geoff 1965
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Re: Hammond Power Transformer Earth ground question

Post by geoff 1965 »

The green/yellow goes to ground where your original green wire did,that’s your filament centre tap.
The red/yellow goes to ground via the HT fuse,that’s your HT centre tap.
Your B+ will be higher than the original “power transformer”so you might need to address that.
Good luck
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joeyello
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Re: Hammond Power Transformer Earth ground question

Post by joeyello »

geoff 1965 wrote:
Sun 10/24/21 9:49 pm
The green/yellow goes to ground where your original green wire did,that’s your filament centre tap.
The red/yellow goes to ground via the HT fuse,that’s your HT centre tap.
Your B+ will be higher than the original “power transformer”so you might need to address that.
Good luck
I have the green/yellow going to the side of the fuse and the red/yellow going to the bottom of the fuse. Is this not correct?
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geoff 1965
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Re: Hammond Power Transformer Earth ground question

Post by geoff 1965 »

Can you add some pics showing how you have wired it?
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joeyello
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Re: Hammond Power Transformer Earth ground question

Post by joeyello »

I believe on the side of the fuse there was another green wire to ground, so my green/yellow is also going to ground.

I’ll have to take the amp apart to take pics. It’s working fine. The noise could be the guitar or the outlet I’m using.
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geoff 1965
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Re: Hammond Power Transformer Earth ground question

Post by geoff 1965 »

There are 2 fuses,one for mains and one for HT,your green/yellow should go straight to ground ”chassis” only the red/yellow goes through the HT fuse to ground.
I would double check it myself to be safe.
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joeyello
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Re: Hammond Power Transformer Earth ground question

Post by joeyello »

Thank you, I will.
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joeyello
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Re: Hammond Power Transformer Earth ground question

Post by joeyello »

Besides the red/Yellow what else goes to the HT fuse?
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geoff 1965
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Re: Hammond Power Transformer Earth ground question

Post by geoff 1965 »

Nothing else just the red/yellow,there should be a wire to ground from the fuse.check it over and add some pics.
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joeyello
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Re: Hammond Power Transformer Earth ground question

Post by joeyello »

This is the original configuration. I believe the yellow on the fuse corresponds to green/yellow on the Hammond and black is red/yellow.

The green wire that is attached with the yellow wire is attached to chassis ground.

I soldered the green/yellow to the side of the HT fuse along with the green wire that was there that goes directly to ground .



D1599722-AFA6-4B78-B18B-4E2F74BD77AC.jpeg
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geoff 1965
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Re: Hammond Power Transformer Earth ground question

Post by geoff 1965 »

Yes that is correct to the schematic,they run the filament CT from the fuse instead of direct to the ground lug,sorry for any confusion!
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geoff 1965
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Re: Hammond Power Transformer Earth ground question

Post by geoff 1965 »

did you notice if your amp has the stock 91R bias resistor?
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joeyello
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Re: Hammond Power Transformer Earth ground question

Post by joeyello »

Ii did not.
Thanks
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colossal
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Re: Hammond Power Transformer Earth ground question

Post by colossal »

joeyello wrote:
Thu 10/28/21 5:46 pm
Ii did not.
Thanks
Is that an 'I did not' in which case, you will look and determine the value for us? Or, is that 'It did not', which means the cathode resistor was not 91R? :lol:
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