Low Hum from Mullard Replica

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Adarsh

Low Hum from Mullard Replica
« on: 26 Feb 2017, 02:04 pm »
Hi

I recently became the owner of a Mullard 5-10 replica. The amp makes a low hum when turned on and nothing connected. Is this noise coming from the tubes?






I get about 30dB when OFF and 35dB when ON. Measured the hum from near the speaker.







FullRangeMan

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Re: Low Hum from Mullard Replica
« Reply #1 on: 26 Feb 2017, 03:22 pm »
I recently became the owner of a Mullard 5-10 replica. The amp makes a low hum when turned on and nothing connected. Is this noise coming from the tubes?
What do you mean say nothing connected?
If its no speakers connected your output transformers will come in short circuit due lack of load (speakers) hence the hum, they will become hot also til something burn.

Adarsh

Re: Low Hum from Mullard Replica
« Reply #2 on: 26 Feb 2017, 05:53 pm »
I'm sorry, I meant to say that I can still hear a hum with no devices connected on the input (ruling out any source that might be causing hum). I have speakers connected on both channels and the hum is coming from the speakers.

shooter

Re: Low Hum from Mullard Replica
« Reply #3 on: 26 Feb 2017, 07:10 pm »
Did you short the input to ground when measuring? If not there will be hum.

FullRangeMan

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Re: Low Hum from Mullard Replica
« Reply #4 on: 26 Feb 2017, 07:22 pm »
I'm sorry, I meant to say that I can still hear a hum with no devices connected on the input (ruling out any source that might be causing hum). I have speakers connected on both channels and the hum is coming from the speakers.
It may be self noise from the circuit, power trafo or OPT, bot the tubes imo.

Adarsh

Re: Low Hum from Mullard Replica
« Reply #5 on: 26 Feb 2017, 07:39 pm »
Did you short the input to ground when measuring? If not there will be hum.
No, I did not. I have read about devices which defeat the ground loop pin but that could have fatal consequences. The AC connector is a schuko type with an integrated ground pin that connects to the terminal in the wall socket.


Adarsh

Re: Low Hum from Mullard Replica
« Reply #6 on: 26 Feb 2017, 07:40 pm »
It may be self noise from the circuit, power trafo or OPT, bot the tubes imo.

I am fairly new to tube amplification. What does one do when faced with this situation? I have never experienced this with solid state amplification.

shooter

Re: Low Hum from Mullard Replica
« Reply #7 on: 27 Feb 2017, 12:18 am »
Let me clarified my comment, I am not talking about lifting the ground on AC, in order to test the noise of your amplifier you have to use a shorting plug on your input RCA to measure, an unconnected open input will have a lot of noise on your speaker terminal.

FullRangeMan

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Re: Low Hum from Mullard Replica
« Reply #8 on: 27 Feb 2017, 11:12 am »
I am fairly new to tube amplification. What does one do when faced with this situation? I have never experienced this with solid state amplification.
Most tube amps have a very low hum when connected to a hi sensitivity speakers, not sure if its your case.
If your prob is a abnormal intense hum you need take the amp to a experiencied tube amp technician.

JohnR

Re: Low Hum from Mullard Replica
« Reply #9 on: 27 Feb 2017, 11:18 am »
Hi

I recently became the owner of a Mullard 5-10 replica.

Noice :D

Quote
The amp makes a low hum when turned on and nothing connected. Is this noise coming from the tubes?

I'm guessing you are talking about mechanical noise from the power transformer.