Crack hum

dead99 · 4563

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Offline dead99

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on: March 01, 2015, 07:43:59 PM
I have posted here before with this problem, strange humming or wistling sounds with my bottlehead crack + speedball that doesn't seem to be EMI and probably it was the 6080 tube.
I have bought a new tube (rca victor 6as7g) but I have noticed that the amplifier physicaly vibrates and that this is what causes the humming noise. If I push down on the tube keeping it from vibrating it is silent. any idea what could cause this?
The new tube has been burned in for ±50 hours, probably even more. amp more like ±250-500 hours.

-dead
« Last Edit: March 01, 2015, 07:49:15 PM by dead99 »


Offline Strikkflypilot

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Reply #1 on: March 02, 2015, 12:20:51 AM
You have fastened all screws?
Could it be that the surface the Crack is standing over is slightly vibrating?

Home system:
Sources: Ibasso DX90, Google Chromecast Audio optical out
DAC: Schiit Gumby
Amp: Bottlehead Mainline
http://bottlehead.com/smf/index.php?topic=7463.0
Phones: HD800S

Office:
Sources: Iphone/ Ipod
DAC: Dragonfly Red+Jtrbug
Amp: Crack/Speedball heavily modded
Phones: HD580,HD600 grilles

Offline dead99

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Reply #2 on: March 04, 2015, 04:22:38 AM
The surface it is on isn't vibrating noticably whilst the amplifier certainly is, an I've checked and all the screws are fastened properly.


Offline Paul Birkeland

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Reply #3 on: March 04, 2015, 06:51:30 AM
How are your voltages?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline dead99

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Reply #4 on: March 06, 2015, 10:43:19 PM
When i finished building and measured the voltages where fine, I will give the precise measurements later today.


Offline dead99

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Reply #5 on: March 08, 2015, 05:59:31 AM
the voltages are
terminal 1 -88.8
terminal 2 -158.8
terminal 3 -0
terminal 4 -158.0
terminal 5 -87.0
terminal 6 -0
terminal 7 -105.5
terminal 8 -0
terminal 9 -104.0
terminal 10 -0
terminal 11 -0
terminal 12 -0
terminal 13 -157.0
terminal 14 -0
terminal 15 -176.0
terminal 20 -0
terminal 21 -194.1

This was measured with my 6AS7G tube

Whilst doing this I also measured my ground line http://bottlehead.com/smf/index.php?topic=4812.0 and it was all 0 ohm


Offline Paul Birkeland

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Reply #6 on: March 08, 2015, 07:58:02 AM
I'd try tightening up the transformer mounting screws.  They should be quite snug.   

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline dead99

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Reply #7 on: March 09, 2015, 08:47:05 PM
I can assure you that all the screws are tightened properly


Offline dead99

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Reply #8 on: March 10, 2015, 06:34:48 AM
I have noticed a odd thing, when I was cleaning my room I tilted the amp and the humming noise partly dissapeared (like 70%)
I dont know why this happends but maybe this helps with finding a sollution.


Offline Paul Birkeland

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Reply #9 on: March 10, 2015, 07:22:58 AM
Sounds like a loose connection in the amplifier.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline dead99

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Reply #10 on: March 10, 2015, 08:16:04 AM
Yeah I agree with you on that, I'll have a look at it when I have time (quite some tests coming up :()


Offline dead99

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Reply #11 on: March 25, 2015, 01:43:04 AM
Ok, so I was away for a bit, not able to take a good look at the amp jet, but the humming noise wierdly dissapeared. instead a wierd wistling has developed. it seems to (mostly) go away after ±30-60 min after turning it on.


Offline dead99

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Reply #12 on: April 30, 2015, 08:11:09 AM
I finally returned with some progress.
1. I checked the whole amp twice togethere with my dad and we found no loose contacts. I resoldered a few connections but that didnt have any effect.
2. I found out that the difference between the 2 tubes can probably be explained like this:
     the 6080 has a wistling noise from the amp
     the 6AS7G has the same wistling noise + a humming sound (I think it broke during shippment (which took 2 months))


Offline Paul Birkeland

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Reply #13 on: May 02, 2015, 07:25:45 AM
Quote from: dead99 on April 30, 2015, 08:11:09 AM
I resoldered a few connections but that didnt have any effect.
I would just resolder them all.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline dead99

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Reply #14 on: May 04, 2015, 03:14:18 AM
okay so I resoldered all the connections I could reach and I think the sound is gone now. I'll see if it returnes over the course of next week but for now it's solved.


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