[danvprod]

Hey all -- hope someone can help me with an intermittent noise problem I am having with one of my 300b monoblock. Amps a 300b + 6sn7 and 6n8p full wave rectifier. DC biased. Having an intermittent crackling noise coming out of my right one. Level of the noise in independent of how hard the amp is being run by the preamp.

I've done the normal troubleshooting things -- tried swapping tubes, cables, but nothing seems to affect the presence of it. Also does not seem to be related to time the amp has been on. Some times the static noise occurs right on startup, in the middle of a listening session or at the end. Lasts for 20 or seconds on average. Then everything is fine.

I've made a video showing the 'condition'. Thank you in advance. http://youtu.be/O-OPjB9cxuM You can hear the problem about :15 into the video.

[Ericus Rex]

First guess is bad solder joint or pin connection at socket.  Try tapping the tubes while on to see if offending socket makes noise.  Are you capable of popping the hood to inspect innards?

[kgturner]

I had an intermittent static-y, crackling noise once as well. I changed multiple tubes and cables. However, I end up finally tracing the sound to a dirty speaker connection. I cleaned all my connections with Caig and haven't heard the sound since. Good luck.

Kevin T

[Ericus Rex]

Kevin brings up a good point.  Clean those tube pins too!

[danvprod]

@EricusRex -- Thanks for the thoughts. I am reasonably comfortable doing some light work inside, but if it is more than some basic work, I've not really worked on tube amps before, and with the high voltages, it makes me a bit leery.

I have contact cleaner, what is the best way to clean the tube sockets? The 300b tubes definitely make a metallic noise through the speakers when tapped (ring or ping), also moving them suspect one around in the socket seems to be affecting the static.

[danvprod]

Also, I recently changed my output system. These 300b are now driving 16 ohm JBL 2446J Compression Drivers > 500 Hz. Is this a really stupid idea, since I only have 8 and 4 ohm output taps?

I've blown two fuses on my left amp (not the one with the static issue) on startup in the last week since powering these CDs.

The static issue seems to be unrelated to my speaker driver change, just more noticeable since the JBLs are 111 dB efficient...

[Ericus Rex]

You're losing a lot of power by using the 8 ohm tap into a 16 ohm speaker, and you may not have power to spare.  If you can get satisfactory volume without clipping from doing this I think it should be ok.

As for cleaning tube sockets and pins, use fine sandpaper on the tube pins then clean with alcohol on a paper towel.  For the sockets, you'll have to try something like a pipe cleaner.  I have a small brush made for cleaning out hearing aids I use on small 9 pins but I don't think that would work so well on larger pins.  Do what you can.

If the noise persists after cleaning you'll have to pop the hood (unplug and let the caps drain for at least an hour before doing this!).  Closely inspect the solder joints to the tube socket.  If they look good then check all other joints in the amp.  Also keep an eye out for any burnt components while you're in there.  If none of this works then I suspect you have a compromised connection within the socket itself.  You may be able to bend something to firm up the connection with the pins or you may have to replace the socket altogether.  And just to completely rule out the problem being in the tube, put the tube of the noisy amp into the other amp and do the tapping/rocking test again.

Best of luck!