Single Rectifier Noise

[sk8erps]

I got a used single rectifier recently. It has el-34's which I def want to replace. My problem is that after the amp warms up for about 15-20 minutes I get a noise coming out of the cabinet that almost sounds like static noise. It only happens in high gain situations ie when I'm in channel 2. I can unplug the guitar cable from the amp and I still get the same noise. Any advice here? I'm thinking tubes b/c I don't have any idea how old they are. Would it be the pre amp or power tubes or neither? Any help would be greatly appreciated.

BTW, got a cool purple jewell lens cover that looks nice.

 

[fluff191]

That would be a preamp tube problem.

Its always a good idea no matter what (unless its brand spanking new) to do a full re-tube of any newly-acquired amp, so you know for yourself the age and condition of said tubes.

 

[sk8erps]

That's a great idea. Looks like I'm buying a bunch of new tubes now.

 

[sk8erps]

How do you test pre amp tubes to see if that's the problem?

 

[fluff191]

While the amp is on and NOT in standby(otherwise you wont hear anything) and a distortion channel lightly tap on the tubes with a pencil or something of that nature. If it starts modulating of making helicopter noises thats your problem. If you hear JUST the actual tap you are probably ok, as you are bound to hear something with that much gain going through the tubes. Hope this helps.

 

[sk8erps]

Thanks fluff. I'll give it a try.

 

[sk8erps]

Here's a vid so you can hear what's going on. As you can see, nothing is plugged into the amp. If I tap on the pre amp tube found all the way to the left looking from the back, it seems really noisy but the others don't make the same noise when I tap them. I don't get a modulation sound or helicopter sound when I tap the tubes. Even the really noisy one. Is this bad pre amp tubes or more serious? Also, I notice the noise calms down sometimes after a while. Meaning it's not as loud.
http://www.youtube.com/watch?v=cOI-Ws6ape4

 

[domct203]

That sounds like a bad jewel lamp cover to me, how did it sound before the swap?

LOL- just kidding.......

Thats a bad preamp tube, most likely V1 or V2.

Dom

 

[sk8erps]

lol too funny. I thought maybe it was the jewell lens replacement.
I'm pretty sure it's the first tube all the way to the left. That tube makes some bad noise when I tap it. Thanks for the help. I'm off to buy tubes today. do I need to just replace the bad tube?

That sounds like a bad jewel lamp cover to me, how did it sound before the swap?

LOL- just kidding.......

Thats a bad preamp tube, most likely V1 or V2.

Dom

 

[domct203]

V1 is the preamp tube closest to the input jack (on the left viewed from the back). This is the input gain stage for every channel and has the most effect on the tone of the amp, good or bad.

You can change preamp tubes at will, pick one up from the local music store and pop it in V1 and see if the problem goes away. If not replace V1 with the original tube and put the new tube in V2. You can safely do this with all the preamp tubes, but it should most likely be V1 or V2. I always shut off the amp first.

You can use any brand 12AX7.

Dom

 

[sk8erps]

Got a new 12ax7 in V1 and replaced the el-34's with 6L6's and this is a whole new beast. The noise went away and I just like the tone of 6L6's way more. Gone is the boxy tone and now I have a nice full rich tone. Thanks to everybody that replied and helped me out. I have now gained some knowledge and my amp is crankin'.