Full Blown Buzz

fuzzman

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Hi all,

I have noticed that when I max out my volumes on my 1987X it makes a full blown *bzzzzzzzzzzzzzzzz* that can only be fixed by lowering it. Even when the volume is at 8-7 it makes this noise.

I know obviously that cranking an amp burns the tubes quicker and some noise will be expected, but before I got my Marshall I'd every so often crank my Fender Hot Rod Deluxe and there was noticeable hum but not as huge and loud as the Marshall. I mean, it sounds bad!

I've owned the amp for about 2-3 yrs. I bought it used, and haven't been able to get the amp maintenance. All these facts may contribute to the noise, course, the noise could be normal, I don't know. I don't have any buddies that own "Plexi" like amps to compare notes to here at home.

So if any of y'all can give me any thoughts that may pinpoint the prob, or just to tell me it's ok, please do. I look forward to any replies.

Thanks.
 

superleadfixer

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That buzzzzzzz, could be a few things, bias set is either to high or to low, huge mismatched of power tubes can be the cause also (over 15-20ma will start doing weird things), a bad tube (dying).... Your grid resistors are failling (not good), etc...

Those it squeal also or just buzzzzing?? If you mouve around does it fades/increaces? Visualy the tubes are ok? (Power tubes should glow blue, no red/orange glow, if so you are red plating meaning your bias is screwed).......check them in the dark, when you play they will vary (color blue..) also as the B+ reduces when playing...etc...

At a certain point with high gain amps you will have noise anyhow...
 

fuzzman

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Hey,

Thanks for the reply "slf"!

No, it never squeals (unless my Fuzz Face volume is past 12:00 but I figured that's just the effect.) It just produced a thick buzz. If I move around there isn't much difference with the magnitude of the noise. Believe me, this is no "60 cycle hum" situation.

Last I looked the tubes seemed to be fine, but you have alerted me to the fact that you say that the tubes should be glowing a slight BLUE?!

Every tube amp I have seen, including my two (Fender HRDeluxe & Marshall), the tubes glow in a nice amber/orange shade... that's bad?

Well, if that's the case I have problems for both my amps!

I'll switch it on tonight and have the lights off to check again of the color of the tubes. I'll keep an update. Thanks again, "slf". As for all the other lil' problems you've mentioned, I'll have to take it to a tech soon to have some diagnosis done.
 

superleadfixer

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ok so we know its not parasitic ocssiation....

That color you just mention could be an under bias situation, the lower the the bias the less blue glow you will have, that is in general depending on tube type. Let say you almost don't have any bias voltage your tube would red plate real bad, dark orange, redish even.....they will just cook themseft real fast and die.......If you would have an overbias you would have strong blue glowing with some red plating but less orange/red then the lower bias situation, then again your tube will go bye bye soon, sound in both case will be all wrong, thinner, less of everything, etc, list goes on and on....

You should bias at around 60-70% of your plate dissipation voltage. That way you will hit the sweet spots and tube life will be great, noise reduce, etc....

Now your problem could be more then just the underbias situation, try to fix that first then see what happens, swap tubes also with healty one you know for sure and see if it still does it, could also be just a bad grounding point in the amp somewhere, that is not a big problem just have to find it and fix it........Have a tech look at it.......
 

linusofriverside

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um there supposed to glow Blue? could you maybe send a pic of this cause ive taken my hot rod to a local amp tech and had it retubed and biased and just done over really nice and it glows orange and so does my dsl but i also have the same buzz when i turn up my treble.
 

superleadfixer

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Blue like a propane flame on a BBQ, at the base of the flame you see the blue color, like that....Check them in the dark, the heaters will also glow orange, all the time of course.... The inner part of the tube will have the blue glow AND when you play the amp it will have variation of the glowing, it follows the B+ ups and downs......a little light show really...

Now check the actual plates of your output tubes (the metal plates are gray usually...) those should not start to glow orange or worst RED, that is an indication of an under bias situation.....Orange should be from the heatrers mainly, verify that by putting the amp in play mode no guitar signal, wait a few seconds and check the plates, at idle like that it will show if a problem, they should be no glow (plates) or barely light orange and fade out when you hit a chord on the guitar (sending signal in the amp).......

If all normal, then your buzz is elsewhere...
 

ripper

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So, I don't mean to butt in but I didn't want to create a seperate thread for a similiar issue. :)

My MG15CD also has a weird buzzing problem I've noticed suddenly. It's not my primary amp and I don't use it much. But as I move the volume control around, the buzzing sound comes and goes; settling at some points, while vanishing at others. It's quite irritating since it's hard to increase or decrease the volume once it's finally clean because it's hard to find a non-buzzing position. And there's no buzzing when I lower the clean volume and hit the overdrive button, except what's to be expected. Anyone got any ideas as to how this can be fixed?!
 

coldsteal2

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Yes tube amps do have a down side if they
are out of wack.
Is it a buzzing or a humming? Hum is normal at high volume
with a strat, or does it buzz without it pluged in also?

to tell the truth it sounds to me like you have a bad
power tube.
 

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