Loud buzzing Noise

Hi,
My GM40 has developed a loud buzzing noise when "Play" mode is activated. The noise comes from the Cab and will also come from the red box if plugged into a desk. The noise remains regardless of whether an instrument is plugged in, and/or the Effects Loop is switched on/off. I've tested and tried different power cables and plug sockets. The noise get louder as you change from Clean through to Ultra channels. The noise does not change by adjusting the master volume.

Would appreciate knowing if anyone else has had the same problem or may not what the fault could be?

The amp is 18 months old, although only had very light use.

Thanks in advance,
Al.

It's mostly likely a tube went noisey on you. Probably a pre amp tube. I'd start there with swapping tubes around to try and isolate the problem tube. You can rule out the power tubes by feeding another amp into the effects return and verify the noise isn't there when doing so. I'd bet if you had another 12ax7 and swapped pre tubes out one at a time you'll find the culprit quickly

AlastairH, I'm having a similar problem. Was it one of the V1/V2 pre-amp tubes? And what did you replace it with in the end?

I bought GM40 in December and I have same problem. Had a gig and it was lots of loud “scratchy distorted” noise they were using several wireless mics for this show and I thought it was interference from them since it was worse when certain actors were on my side of stage. But for next show today it made the noise as soon as I switched out of stand by. Brought back up amp and used that today. So I guess it’s bad tubes (valves). After only 3 months of light usage and first time I started using it to gig.

Yup same problem. I've had this before with a new GM40D after a few months and the shop exchanged it for a new one under warranty. Now a year later it's happening again and I could go through the same process but frankly I can't live without an amp for 3 weeks. The noise is on all channels, with nothing plugged in. Master volume makes no difference so I expect its one of the power amp tubes playing up. I think the trick is to carefully remove the top casing and tap on the tubes to see which one is the culprit? And while I'm at it I'll replace all the tubes/valves with 2 matched pairs of JJ EL84s in the power amp section and 3 x JJ 5751 for the pre-amp as a lower gain substitute for the ECC83S/12AX7s. Not sure if the V3 phase converter needs changing though.

So today I spent some time testing things. When i first started I let the amp warm up. Took it out of stand by and got some of the noise played through it and it decreased. I noticed one of the power tubes (the inner right ) was completely glowing. Not like the others but the whole tube was orange. I reached for my phone to take a photo of it and it faded. And didn’t do that again. The scratchy distortion noises stopped and I played loud on all the channels. Switching from 40 to 20 to 5 to 1 when I pushed a guitar pick into the test slot the lights blinked 12 times
So maybe I need new tubes if it’s going to be an intermittent problem. I don’t want to gig with it knowing it can do this at anytime. I had emailed H&K when it made the squealing sounds and got no response. I’ve had it for 95 days so I guess the tube warranty expired. I’ve emailed sweetwater where I purchased to see what they say about it.
If I get new tubes. I’d like to get some that are warmer and darker sounding. The amp is a little bright. Can you guys recommend new tubes ?

I took the lid off (3 screws each side, loosen but leave on the bottom 2) and when the squeal happened tapped on each of the tubes with a pencil to find the culprit. Turns out it was one of the EL84 Power Amps tubes. I've ordered a set of matched JJ EL84s and while I'm at it I'll also replace the pre-amp tubes with two JJ 5751s which will hopefully make it less harsh. Then I can use the Lead and Ultra channels without having the gain set between 1-2.

I’ve got a sweetwater support ticket going now. I’m pretty sure it’s one of the tubes and I think it’s one of the EL84 also when it was making the noise one of them was completely glowing I went to get my phone to take a photo but it faded. Still making the sound but it’s intermittent
I read the whole GM36 tube thread and agree with your choices for new tubes. The only one I’m unsure about is V3. Are you switch that to a 5751 also? I agree it can be less gain and be better for the style of music I play and there’s more knob left on the gain under the ultra and lead channels. I would also like less brightness. My Gibson Les Paul with some vintage pickups sounds horrible. But great in my Mesa mark V:25. I’ve heard it described as Fizzy on these forums. If I can get that under control and a little less gain. This will be perfect. I do like the amp

I'm no expert either and haven't decided yet whether to swap out the V3 Phase Inverter. From what I read in other forums its best to keep a 12AX7/ECC83S in V3 and don't replace with another of lower current. I also read JJs don't fair well in V3. But like I said I really don't know. My new JJ tube set arrives tomorrow so I'll hear if my ears can tell.

Please post your opinion I am seriously thinking of the exact same tubes.

Hopefully this advice can be of some help to you guys. Unfortunately what you guys are experiencing is low quality of the Chinese tubes the amp ships with. The harshness complaints...again the Chinese tubes. If you guys are going the JJ tube route I'd strongly suggest getting them from Eurotubes as they do a great job of testing and weeding out the duds. Also if you call they will give you a specific set of the 3 different variations of the 12ax7 JJ makes to suit your needs. They can get lower or higher gain examples and take out the guess work. Now regarding the glowing power tube. That's called red plating. It can be as simple as just a defective tube or it can be something more serious. So if you see that happen again after putting in the new tubes shut it down immediately and seek out a amp tech. I got one of the first GM40's that hit the shores of USA when they came out and though I don't gig I do play mine several hours a week. These amps and lots of other modern el84 amps seem to be hard on the phase inverter tubes and they are frequently the noisey tube. In the first year my amp ate 2 of the Chinese tubes up in the PI slot. Since then and going on 2 years I've had the same old long plate Mullard in my PI and it's still going strong. For the future you guys may want to consider looking into getting some of the good old tubes that are still out there. You can still buy great NOS tubes for close to the same money as new production tubes. I'm not talking about the Mullards and Amperex tubes going for crazy money but there are lots of nos GE, Tung sol, Sylvania's etc that can still be had for affordable money. Not only will they sound better but their life span will put to shame any of the new stuff out of Russia and China. Especially if you're going the 5751 route as there are plenty of cheap nos stuff available. The new tubes simply don't hold up like the old production stuff does. Plenty of other guys will tell you same thing. It's not uncommon to go through two set of new production tubes while one set of old glass will still be holding up great. I've auditioned dozens of both new production and nos tubes through my gm40 and I think the new production Tung Sols sound great. If going with JJ I vastly preferred the mid length and long plate 12ax7 over their short box plate version for they sounded much less harsh. No matter what pre amp and power tubes you choose if you want probably the best new production PI option available for durability I highly recommend the Sovtek LPS 12ax7 in the PI over anything currently available new

Thank you Irondave12. Great help.  So since I only bought my GM40 3 months ago, I emailed Sweetwater, described the issue and they agreed it was a tub problem.  the one that Redplated was the Power Tube 2 I guess it would be the second Power tube from the input side.  They shipped a new replacement amplifier to me today which I should have by Friday for my gig this weekend.  Great !

happy about that.
but I was looking forward to getting some less harsh tubes and I will be changing out the Chinese ones also.  I also did that when I bought an ART and a Presonus Tube preamps a couple years ago, I didn't even power them on until I changed the tubes.

I also play with a Mesa Mark V 25 and my Gibson Les Paul with Brandonwound pickups sounds amazing and I really can control the amp with my guitar volume and tone knobs. but it just sounds horrible in the GM40 I have tried and tried to get good tone with it but it has that harshness and is way too bright.  I have a Dream Studio guitar with Seymour Duncan Seth Lovers in it and it gets good tone from the GM40  so I chose the guitar based on the amp I am using  
for speakers I play through a Jensen Vintage Alnico 2 15" speaker in a custom cabinet and a Marshall 4-12 that I put a pair of WGS Veteran 30 and a pair of WGS ET65. wired separately like it's 2 2-12 cabinets

I like rock and blues. I do like versatility in tone but prefer warm and creamy to harsh and brittle  

I would happily trade some gain out of the GM40 for some smoother sound.

I think I am going with some 5751 for preamp 1 and 2 and the sovtec 12ax7 you recommended for PI
and JJ EL84 power tubes.  
I just don't know if I'm going to play it as it is for a while first .

I have a show Friday night and 2 shows Saturday that I really want to use the GM40 for due to the variety of tones available without pedals
after that I am just practicing and writing with drummer and singer and I have usually used my mesa for that ..... I may do two more shows in may but I haven't committed to them yet but I need to this weekend,

Really do appreciate your advice Irondave12  I'm going to at least start looking now. I will definitely talk with Eurotubes.  Nice to have a reliable and reputable supplier for things.  I'm very happy now that I bought the amp from Sweetwater. they are really stepping up replacing it.  I didn't expect that.. they said other mfg would have them ship new tubes but H&K just wants to swap out the amp

I'm completely against cheap Chinese crap for materials.

yeah good advice there Irondave12, thanks. One question - how much effect will replacing the PI have on the overall tone of the amp? Also is it true that the PI tubes must be balanced?

Because of the push pull operation of the amp they strongly suggest having a balanced PI tube but it's not absolutely necessary and won't hurt anything not having one. Some say it sounds good not having a balanced signal hitting the power section. I haven't experimented yet in that area. The PI choice shouldn't impact the tone in a noticeable way to most people ears but some people swear it does. I was told years ago to start using long plate tubes in the PI slot and once I started it did seem to make my amp sound a little less fizzy. I recommend the Sovtek LPS as its a long plate tube with welded plates and has a reputation for holding up better than others doing the PI job. The V1 and V2 pre amp tube slots are where you're going to notice the most change. I have all high end NOS tubes in my amp and just love the combination I currently run. But you guys could do well running the JJ in the power section, the Sovtek in the PI and eventually look for a couple affordable nice old tubes for the 2 pre amp slots. You don't need NOS tubes either. There are tons of barely used vintage tubes to buy cheap on the market which will give years of service still. As long as you're buying from a seller that does proven testing on what they sell that's where the best bang for your buck in tubes lies. I've scored many great tubes that way. Keep in mind tubes are just a part of the tone tools. The best gains in my amp came from speaker testing. IMO the v30 speakers do the gm40 a disservice for music that's not high gain. You're on the right track with an alnico speaker as it will tame some highs and brightness. I finally settled on a vintage celestion blackback and the new alnico creamback in my two 1x12 cabs and probably won't change again since its the perfect balance for me with a variety of music types I play