Loud sudden rumbling when turn on amp

andy2 · 18th February 2006, 10:04 PM

Is it normal when I turn on my tube amp, there is a short rumbling sound from the speaker?

Here is the schematic of the amp:
http://www.geocities.com/hai_vu1/schematic.JPG

It is a push-pull using 2 300B tubes.

Tube_Dude · 18th February 2006, 10:15 PM

Are the two cathodes of the input tube connected to each other?

In the schematic they are not, but they must be...

Colt45 · 19th February 2006, 07:39 AM

yeah, that would do it.

Tube_Dude · 20th February 2006, 01:57 PM

So?

andy2 · 20th February 2006, 04:54 PM

Quote:

Originally posted by Tube_Dude
So?

Sorry for the delay. But I was looking at the schematic myself and the input stage doesn't look like a diff stage so I am not sure if they are supposed to be connected together.

I haven't gotten a chance to open up the amp and look at it yet. But I have a picture of the amp internally:
http://www.geocities.com/hai_vu1/mingda.JPG

I am not sure if the picture can tell.

By the way, the initial noise because I think I don't have any mean to slow down to initial inrush current at start up. So I have to come with a way to limit the current when turned on.

The simplest way is to use a thermister between the rectifier and the power decoupling caps.

Thanks.

SY · 20th February 2006, 06:10 PM

The input stage appears to want to be two triodes connected in parallel. So since you have plates tied together, grids tied together, you absolutely need to tie the cathodes together. Trying to use the capacitor as a ground return on that second section will definitely not benefit you!

rcavictim · 20th February 2006, 08:21 PM

I suspect the error is in the schmatic only and not in the wiring of these amps. I also can not see how this would cause instantaneous startup noise since the strapping of both cathodes of the input 6SL7 is meaningless until the cathode reaches emission temperature which will take a good 8-10 seconds.

I am also aware of this problem and would like to know the sulution. A friend has it in his MingDa and is too far for me to get the amp to sort out on my bench. He has reported an accompanying flash inside one of the 300B tubes. Unfortunately he has ElectroHARMonix gold grid 300B's in his amp and in my experience with this brand 300B, they do this normally. Pure overhyped garbage IME.

andy2 · 20th February 2006, 08:49 PM

Quote:

Originally posted by rcavictim
I suspect the error is in the schmatic only and not in the wiring of these amps. I also can not see how this would cause instantaneous startup noise since the strapping of both cathodes of the input 6SL7 is meaningless until the cathode reaches emission temperature which will take a good 8-10 seconds.

I am also aware of this problem and would like to know the sulution. A friend has it in his MingDa and is too far for me to get the amp to sort out on my bench. He has reported an accompanying flash inside one of the 300B tubes. Unfortunately he has ElectroHARMonix gold grid 300B's in his amp and in my experience with this brand 300B, they do this normally. Pure overhyped garbage IME.

Could you be a little specific as to what problem he is experiencing? It could help me.

As for the tube flasing when turned on, is this normal or could signal some abnomality?

Thanks.

rcavictim · 21st February 2006, 05:21 AM

Andy,

You have PM.

anatech · 21st February 2006, 01:51 PM

Hi Andy,
Any chance of trying another pair of 300B's? You will need to use them later at worst, at best this will fix your problem.

-Chris

18th February 2006, 10:04 PM	#1
andy2 diyAudio Member Join Date: Nov 2004 Location: Los Angeles	Loud sudden rumbling when turn on amp Is it normal when I turn on my tube amp, there is a short rumbling sound from the speaker? Here is the schematic of the amp: http://www.geocities.com/hai_vu1/schematic.JPG It is a push-pull using 2 300B tubes.

18th February 2006, 10:15 PM	#2
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	Are the two cathodes of the input tube connected to each other? In the schematic they are not, but they must be... __________________ Jorge

20th February 2006, 01:57 PM	#4
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	So? __________________ Jorge

20th February 2006, 06:10 PM	#6
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	The input stage appears to want to be two triodes connected in parallel. So since you have plates tied together, grids tied together, you absolutely need to tie the cathodes together. Trying to use the capacitor as a ground return on that second section will definitely not benefit you! __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

20th February 2006, 08:21 PM	#7
rcavictim diyAudio Member Join Date: Jun 2004 Location: Cool end of a soldering iron NW of Toronto	I suspect the error is in the schmatic only and not in the wiring of these amps. I also can not see how this would cause instantaneous startup noise since the strapping of both cathodes of the input 6SL7 is meaningless until the cathode reaches emission temperature which will take a good 8-10 seconds. I am also aware of this problem and would like to know the sulution. A friend has it in his MingDa and is too far for me to get the amp to sort out on my bench. He has reported an accompanying flash inside one of the 300B tubes. Unfortunately he has ElectroHARMonix gold grid 300B's in his amp and in my experience with this brand 300B, they do this normally. Pure overhyped garbage IME. __________________ I.Q.Test. Have you ever purchased a recreational snowmobile?

19th February 2006, 07:39 AM	#3
Colt45 diyAudio Member Join Date: Feb 2002 Location: Canada	yeah, that would do it.

21st February 2006, 05:21 AM	#9
rcavictim diyAudio Member Join Date: Jun 2004 Location: Cool end of a soldering iron NW of Toronto	Andy, You have PM. __________________ I.Q.Test. Have you ever purchased a recreational snowmobile?

21st February 2006, 01:51 PM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Andy, Any chance of trying another pair of 300B's? You will need to use them later at worst, at best this will fix your problem. -Chris

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