Tube problems... Amp gurus get in here!!!

[AHChris]

Hey guys!

I have some problems with my triple rectifier lately. When I play rather quiet (it doesn´t gets louder when I turn the volume up) I get a really deep humming noise. I thought ok no problem, microphonic preamp tube, got a spare one from the rehearsal room and tapped on the tubes with a pen while powered on. No preamp tube microphonic... But when I tap the right power tube, the humming starts and stops from time to time.

You can hear it here: http://dl.dropbox.com/u/4195368/Recto.mp3

Also 3 of my power tubes are glowing blue... I know this can be normal but I thought I could mention it

Here´s a pic. It´s a bit dark, but you can see it´s the first (the one that I tapped in the audio file), the second, not the third but the fourth again (can´t see it in the pic) glows blue.

What do I have to do? Power Tube change? Wolfe? Lasse? Anyone?

 

[TheWinterSnow]

Obvious thing to do is replace the tubes, but it sounds like one of the tubes is bad and the other has gone microphonic (although rare, pentodes can still become microphonic). With having one tube microphonic and the other most likely dead you will have a current imbalance in the transformer which can cause hum. Then you have the noise from the tapping the tube which adds more noise.

The blue glow is normal, a tube not even glowing the faintest of a dark blue is a sign that either its dead, or you have a failed screen grid resistor.

 

[Omega_Void]

...current imbalance in the transformer which can cause hum...

Yup. Since the noise goes away temporarily the tube must be working. I'd guess the pins aren't all making good contact with the socket.

I've heard it remarked that some JJs power tubes have noticably slimmer-than-standard pins, BTW.

You could try bending the socket contacts in a bit so they grip the pins better, but you need to be sure the capacitors in the amp are discharged before you stick anything conductive in the socket.

 

[AHChris]

Yup. Since the noise goes away temporarily the tube must be working. I'd guess the pins aren't all making good contact with the socket.

I've heard it remarked that some JJs power tubes have noticably slimmer-than-standard pins, BTW.

You could try bending the socket contacts in a bit so they grip the pins better, but you need to be sure the capacitors in the amp are discharged before you stick anything conductive in the socket.

I´ll try to put some caramba / WD40 on the pins and put them in and pull them out a few times... maybe it helps. I don´t have JJs, I have =C=

I am reaaaly careful when it comes to tubeamps because of my limited knowledge about capacitors and lethal electric shocks But just out of curiosity: how do I discharge the capacitors?

 

[Wolfeman]

But just out of curiosity: how do I discharge the capacitors?

They 'should' discharge on their own in a Rec after you turn it off. Usually takes a few minutes for them to completely drain. Unplug the wall cord, and check with a multimeter.

If they still have a charge, just put a resistor across it's leads. I usually just grab a 1 watt resistor, size really isn't crazy important, a 470ohm to 220k should work.

 

[AHChris]

They 'should' discharge on their own in a Rec after you turn it off. Usually takes a few minutes for them to completely drain. Unplug the wall cord, and check with a multimeter.

If they still have a charge, just put a resistor across it's leads. I usually just grab a 1 watt resistor, size really isn't crazy important, a 470ohm to 220k should work.

Ok I have no resistors in range and I really think I´m to much of a tube-noob to do such things... I´m to young too die from a horrible accident with my beloved wattmonster^^ what´s your suggestions to my problems wolfe? Power tube fail? I changed them not too long ago and I don´t have the money for another tube set right now, especially because I need a matched sextett...

 

[Omega_Void]

Swap the power tubes around in the sockets, and do the tapping thing again.
If the problem goes away when you tap the tube in a particular socket, it's the socket.
If it goes away when you tap a particular tube, it's the tube.

 

[AHChris]

Swap the power tubes around in the sockets, and do the tapping thing again.
If the problem goes away when you tap the tube in a particular socket, it's the socket.
If it goes away when you tap a particular tube, it's the tube.

Haha haven´t thought of that before^^ I´ll try that for sure! I hope its not the socket

 

[Wolfeman]

Sometimes just pulling out the tubes and putting them back in solves the problem