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Old 27th October 2004, 06:44 PM   #1
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Default earthing!!!!!!!!!!

The amp is ready!!
Now it's my first 5 min. I listen to it!!!

BUT hummmmmmmm.

I use a bus bar from the input RCA to output tranny.Not FDB,yet.
And ground them at the chassis between them.I didn't use any cap or resistor.Will this solve the problem???

PSU and all caps are grounded separetaly and they go to chassis with the main ground and CT of filaments at another place.

What to do?
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Old 27th October 2004, 07:05 PM   #2
845 is offline 845  Israel
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Hi resident!
There can be you have chosen a wrong place for the output transformer in relation to the power transformer?
Try to turn or move it .
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Old 27th October 2004, 08:15 PM   #3
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Default Re: earthing!!!!!!!!!!

Quote:
Originally posted by resident
The amp is ready!!
Now it's my first 5 min. I listen to it!!!

BUT hummmmmmmm.

I use a bus bar from the input RCA to output tranny.Not FDB,yet.
And ground them at the chassis between them.I didn't use any cap or resistor.Will this solve the problem???

PSU and all caps are grounded separetaly and they go to chassis with the main ground and CT of filaments at another place.

What to do?

What kind of hum is it? I mean, is it a clean, 'round' sounding 50Hz? In that case you probably pick it up as said above from the transformer or wiring.

Does it sound with a rattling, 'sharp' character? In that case, it probably is supply current resulting from incorrect grounding scheme.

Jan Didden
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Old 27th October 2004, 09:04 PM   #4
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Quote:
And ground them at the chassis between them
Quote:
PSU and all caps are grounded separetaly and they go to chassis with the main ground and CT of filaments at another place.
It looks like the chassis is used as part of the ground.
In this way you get a ground loop, and hummmm.
It is most important that you have only one connection from your ground to the chassis.

Dick.
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Old 27th October 2004, 10:33 PM   #5
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I LIKE THIS FORUM!

Thank you guys for your help.

@ 845
Quote:
There can be you have chosen a wrong place for the output transformer in relation to the power transformer?
I don't think it's over here the problem 'cause the power in relation with OPTs are at 90 degrees.The power tranny is vertical and the OPTs are horizontal.
@janneman
Quote:
What kind of hum is it? I mean, is it a clean, 'round' sounding 50Hz? In that case you probably pick it up as said above from the transformer or wiring.
I'm not very experienced on hummm sounding.I think it's clean 50Hz.It's like "vvvvvvvvvvvv"!
@Dick
Quote:
It is most important that you have only one connection from your ground to the chassis.
How to do this right now?
My inputs are at the front of the chassis (near the input tube) and the PSU at the back.
Do you believe it will be better to use a thick wire from the front of the chassis to back and ground it over there with the other grounds?


I saw that many use a cap or resistor to ground the circuit earth.
Maybe this will solve my problem.What do you say?

An other problem that I have is that my tubes are getting too blue.Is this normal with 6L6s at 430V and Ia 65mA?
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Old 28th October 2004, 03:39 AM   #6
845 is offline 845  Israel
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Quote:
An other problem that I have is that my tubes are getting too blue.Is this normal with 6L6s at 430V and Ia 65mA?
6L6 is beam tetrode,blue glow in beam tetrode this usual phenomenon.

You can reed about blue glow here :
http://www.jacmusic.com/html/article...w/blueglow.htm
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Old 28th October 2004, 08:04 AM   #7
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thanks for the link.
I have started to worry.

I'm going to my bench,right now to see what I can do with my hum problem.
Hope I'll solve the problem!
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Old 28th October 2004, 08:53 AM   #8
SHiFTY is offline SHiFTY  New Zealand
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First of all, is it a hum or a buzzzz? Is it coming from any of the transformers? Does it increase or decrease with the position of the volume knob? Have you definitely got something plugged into the input...

I would run a star type earthing system. Use a single point on the chassis for earthing. Run one earth wire from the input jacks and volume control, one wire from the preamp tube cathodes resistors, one wire from the power tube cathodes resistors, one wire from all power supply earths, and one from the output transformer ground.

This kills earth hum in 99% of all my amps...
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Old 28th October 2004, 10:29 AM   #9
DIAR is offline DIAR  Finland
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Is there required grounding in tube socket pins.
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Old 28th October 2004, 11:22 AM   #10
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Hi Shifty
Itís a hum (I think so).Itís the same sound that power transformer produces.
If I get close my ear to power transformer I here the same sound I have to my speakers.
Hope the fault is not by the positioning of transformers. Theyíre at 90 degrees as I said.
I also donít use chokes.

With grounded inputs the hum is the same to both channels.
With open inputs, one channel hums louder.
If I connect a preamp to it and the volume of preamp itís at zero I have more hum than I have with grounded inputs. And itís audible at low levels but, the same at both channels. And it doesn't increase with different volume levels.

Things got better when I change the wire that connects the input tube with the phase splitter with a shield wire. So, I believe my problem is on wiring. I think Iíll try star earth. What do you say to try something like this in the attached foto.

Now I use a bus bar from the RCA inputs and follow the signal until the OPT. And I grounded them between the RCA at the chassis.
The supply starts from the first caps of the PSU and continues with a twisted wire until the last cap near the input tube. This ground is taken from the first cap of PSU and goes to chassis with the main earth and CT of filament windings.

Please help me guys Ďcause I love the sound of this 6L6GC UL amp. And I havenít use feedback, yet. Also, not any matching of the signals at the outputs of the phase splitter. I havenít tested different bias at the 6L6. Now Iím at 65mA and Va at 420V.
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