I have a buzzing sound for the first minute after turning on the amp, it is only happening on the distortion channel after minute or so it disappears. I tried changing 12ax7's but it did not help, power tubes neither. Any ideas please...
The only thing I did before this started happening is that I got new 6L6's in. Now even if I put the previous EL34's back in I still have the buzz. Could this have caused the problem or it's just a coincidence??? (Laney has a biasing switch and I'm always using it properly).
PS I tried shaking wires, checked connections, does seem to be problem of that sort.
First make sure no interference type devices are nearby, dimmers, PC's, cell phones, etc.
Since this is a PCB amp, are the sockets mounted on the PCB?
If so, sometimes a trace can be cracked by flexing the PCB when pulling and inserting a tube.
I know these little bugs, like buzzing for a minute then stopping can drive you crazy but intermittent problems such as these can be difficult to trace.
Try to figure out what stage is causing the buzz by isolating the channel that is buzzing.
This can involve pulling all tubes for each channel to see which channel is the culprit.
Yes ten tubes, tubes mounted on the metal chassis, not under warranty, amp made in 90's. Here is the schematics plus a photo of an open amp... Buzzing only on the distortion channel and only when turned on for a minute or so.
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If the problem goes away... has the amp been dropped, moved while hot, driven around or shipped roughly recently?
These are usually signs of a cold solder point as the voltage heats up the joint it flows and makes connection.
I'm rather doubtful it's tube related unless it's at a socket. tubes once they start going bad tend to get worse not better. however you may have a gassy tube.
Yes, the amp has been on the road this weekend, I am just now going around re-soldering and cleaning connections.. hope that will solve the problem, but keep ideas coming guys....
PS as I mentioned above I tried changing all the tubes the problem did not go away.
Another thing to check is the FX loop jacks, the switch sometimes gets oxidized causing problems.
But this amp appears to use Cliff jacks which are kind of self cleaning.
Pretty hard to chase a problem when it doesn't last long.
Well it seems I solved it, the amp has been on the road this weekend and I have also done some fast soldering a moth ago, seems that I had a bad soldering around 12ax7's for distortion channel that got worse by rough handling on the road. I detached all the connections, cleaned and re-soldered, spent whole night trying out, warm, cold and problem has not returned
To avoid this in the future give the amp time to cool before you move it. It most likely happened after a quick gear pull the head was set down hard while hot. If possible give the amp 5-10 minutes to breathe before you move it. This will also help increase tube life. Start with the pedal board cables and drums move the amps last.
after minute or so it disappears. I tried changing 12ax7's but it did not help, power tubes neither. Any ideas please...
