problem - scratchy sound, rythmical

adamus · 06:58 PM

I bought a cheap el34 valve amp to play with (it was sold as not working).

I have revived it by replacing coupling caps, a new set of valves (used 6pS3) and replacing the cathode resistors of the input stage.

All biases up fine, plays music..... but. There is a constant but quiet rythmical noise, scratchy noise.

to a beat of around 2 a second it has minor bursts of noise.

Anyone have any ideas of where to start?

Edit - And its from both speakers. Seems like B+ or maybe the screen supplies.

adamus · 14th October 2009, 08:32 PM

I pulled all the input tubes, and the noise went. Put some old crap chinese 6n1 in, and the noise is gone.

Must be a couple bad 6n1p's, unless anyway can think of a reason why 6n1p may do this over the 6n1?

adamus · 14th October 2009, 09:12 PM

scratch that. the noise is back. I dont think its B+ or output tubes, as without the input tubes in there is no noise.

aardvarkash10 · 14th October 2009, 10:07 PM

schematic?

Enzo · 15th October 2009, 03:19 AM

Got a cell phone sitting near it?

Also, set up an AM radio next to it, tune to where there is no broadcast and listen if the radio picks up the same noise. Angle the radio different directions, as they do pick up directionally.

adamus · 15th October 2009, 06:17 AM

I dont have a schematic (havent drawn one yet) but after a quick look it looks like a phase splitter to SRPP to output stage.

I dont think its interference, its not that typical buzzing you can get.

aardvarkash10 · 15th October 2009, 08:03 AM

well thats an odd architecture... to me anyway. I was more interested in the power supply configuration since it seems to be related to that frequency

HollowState · 15th October 2009, 03:13 PM

Quote:

Originally Posted by adamus

I dont think its interference, its not that typical buzzing you can get.

Regardless of what you do or don't think, interference comes in many forms. Enzo gave you some good advice and is a proven diagnostic tool. And now is the time for the oscillocsope to be brought out and used as a signal tracer. If I could have only one instrument on the test bench, it would be the scope. With it you can replace the function of many instruments. It's really indispensable as a troubleshooting tool.

adamus · 15th October 2009, 05:19 PM

I have a scope, and will be using it tonight.

Will report back. cheers for the input

adamus · 15th October 2009, 05:57 PM

ok i scoped various points and nothing, looked ok, a bt too much ripple on B+ for my liking but that can be sorted.

then i plugged the speakers back in.... and nothing, no noise.

Then i turn the amp over to its (it was upside down for testing).... and the rustle is back.

This ihas to be mechanical or heat.

14th October 2009, 06:39 PM	#1
adamus diyAudio Member Join Date: Apr 2008	problem - scratchy sound, rythmical I bought a cheap el34 valve amp to play with (it was sold as not working). I have revived it by replacing coupling caps, a new set of valves (used 6pS3) and replacing the cathode resistors of the input stage. All biases up fine, plays music..... but. There is a constant but quiet rythmical noise, scratchy noise. to a beat of around 2 a second it has minor bursts of noise. Anyone have any ideas of where to start? Edit - And its from both speakers. Seems like B+ or maybe the screen supplies. Last edited by adamus; 14th October 2009 at 06:58 PM.

14th October 2009, 10:07 PM	#4
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	schematic? __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

15th October 2009, 08:03 AM	#7
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	well thats an odd architecture... to me anyway. I was more interested in the power supply configuration since it seems to be related to that frequency __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

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14th October 2009, 08:32 PM	#2
adamus diyAudio Member Join Date: Apr 2008	I pulled all the input tubes, and the noise went. Put some old crap chinese 6n1 in, and the noise is gone. Must be a couple bad 6n1p's, unless anyway can think of a reason why 6n1p may do this over the 6n1?

14th October 2009, 09:12 PM	#3
adamus diyAudio Member Join Date: Apr 2008	scratch that. the noise is back. I dont think its B+ or output tubes, as without the input tubes in there is no noise.

15th October 2009, 03:19 AM	#5
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	Got a cell phone sitting near it? Also, set up an AM radio next to it, tune to where there is no broadcast and listen if the radio picks up the same noise. Angle the radio different directions, as they do pick up directionally.

15th October 2009, 06:17 AM	#6
adamus diyAudio Member Join Date: Apr 2008	I dont have a schematic (havent drawn one yet) but after a quick look it looks like a phase splitter to SRPP to output stage. I dont think its interference, its not that typical buzzing you can get.

15th October 2009, 05:19 PM	#9
adamus diyAudio Member Join Date: Apr 2008	I have a scope, and will be using it tonight. Will report back. cheers for the input

15th October 2009, 05:57 PM	#10
adamus diyAudio Member Join Date: Apr 2008	ok i scoped various points and nothing, looked ok, a bt too much ripple on B+ for my liking but that can be sorted. then i plugged the speakers back in.... and nothing, no noise. Then i turn the amp over to its (it was upside down for testing).... and the rustle is back. This ihas to be mechanical or heat.

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