Crack hum

[dead99]

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

 

[Strikkflypilot]

You have fastened all screws?
Could it be that the surface the Crack is standing over is slightly vibrating?

 

[dead99]

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.

 

[Paul Birkeland]

How are your voltages?

 

[dead99]

When i finished building and measured the voltages where fine, I will give the precise measurements later today.

 

[dead99]

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

 

[Paul Birkeland]

I'd try tightening up the transformer mounting screws.  They should be quite snug. 

 

[dead99]

I can assure you that all the screws are tightened properly

 

[dead99]

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.

 

[Paul Birkeland]

Sounds like a loose connection in the amplifier.

-PB

 

[dead99]

Yeah I agree with you on that, I'll have a look at it when I have time (quite some tests coming up )

 

[dead99]

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.

 

[dead99]

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))

 

[Paul Birkeland]

I resoldered a few connections but that didnt have any effect.

I would just resolder them all.

-PB

 

[dead99]

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.