#1
I got a Peavey 6505+ 112 around a year ago. But last week it started making this popping/crackling sound, even when no guitar or anything else is plugged in.

I figured the tubes might be going bad since I got it used and haven't replaced any of them yet. I used some canned air and sprayed out the connection areas of both the tubes and where they plug in, but the popping/crackling sound persisted. I did this only to the two power tubes.

Today I went and bought a pair of Electro-Harmonix 6L6GC power tubes as a replacement. The stock tubes have "Ruby 6L6GCM-STR" printed on them.

Here's my questions:

1. I can use these new tubes without ruining my amp or the tubes prematurely, right? The box says "6L6GC" but the actual tube has "6L6EH" printed on it. I'm fairly sure this amp has a fixed bias, and I'm new to tubes so I'm just not sure.

2. What could be causing this extra noise if putting in these new tubes doesn't fix it?

Thanks.


In my restless dreams...
I see that town.
Silent Hill.
You promised you'd take me there again someday.
But you never did.

Well, I'm alone there now.
In our 'special place'...
Waiting for you.

#2
1 6L6EH is the company marking, stands for Electro Harmonix. Should still be a standard 6L6GC. Yes you should be able to use them without ruining anything. Any 6L6GC tube should work in that amp. Some of mine just have 6L6, no suffix.

2. If it's not tubes causing it, when resistors get old they can start to make a sizzling sound like bacon frying, they develop tiny hairline cracks after a few years of heating and cooling, and start to get noisy. Usually this will be the older carbon comp type resistors. I had a few doing the bacon sizzling thing in my Super Reverb a while back. It's back now, but only in the reverb section, next time I open up I'll be taking a look at those. For now I don't use reverb anyway and turned off it's quiet.

Also, most amps should be biased when you change tubes. It can be played and probably won't do any damage, but check with a qualified tech to be sure how to handle it with that particular amp. Don't open it up yourself unless you know what you're doing, tube amps have capacitors that store high voltage for several months after being unplugged, it is literally deadly in there.

One more thing, preamp tubes can also be causing the noise you're referring to. One of my brand new preamp tubes, the same 12AX7A that's probably in that amp, got a loud pop when I turned the amp off. I swapped it to a different position and it works fine. It's been pulled since then, I think it's in my box of spares. But check your preamp tubes too. Get one or two, swap them one at a time and see if the noise stops. When it stops, you found your weak tube. You might also be able to take them to a tech and have each tube tested, check around and see who does good work in your area.
Hmmm...I wonder what this button does...
#3
Quote by Paleo Pete
Also, most amps should be biased when you change tubes. It can be played and probably won't do any damage, but check with a qualified tech to be sure how to handle it with that particular amp. Don't open it up yourself unless you know what you're doing, tube amps have capacitors that store high voltage for several months after being unplugged, it is literally deadly in there.


I just read on another forum from a Peavey rep regarding this exact amp:

"The bias is fixed, and non-adjustable. No adjustment is required when changing tubes"

So does that mean I'm pretty much good to go on changing any tubes? I'm going to check the preamp tubes like you said as well. Thanks so much for your thorough answer as well.


In my restless dreams...
I see that town.
Silent Hill.
You promised you'd take me there again someday.
But you never did.

Well, I'm alone there now.
In our 'special place'...
Waiting for you.

#4
Quote by Alpha_Wolf
I just read on another forum from a Peavey rep regarding this exact amp:

"The bias is fixed, and non-adjustable. No adjustment is required when changing tubes"

So does that mean I'm pretty much good to go on changing any tubes? I'm going to check the preamp tubes like you said as well. Thanks so much for your thorough answer as well.


yeah you can just change the tubes and be good to go.
#5
With the fixed bias, just make sure you are using the same type of power tube. 6L6. Preamp tubes do not require biasing.

The noises you are talking about are more common with bad preamp tubes. Tap the preamps with the eraser end of a pencil with the amp on, off standby, to see if you hear anything gross.

Use contact cleaner (Deoxit) instead of compressed air.

Next time when you are buying tubes, try to get a brand better than EHX (or JJ or GT). Although those tubes will work, brands like Tung Sol, Tube Amp Doctor, and Mullard make better tubes. c:

Lastly, you might want to read through this: https://www.ultimate-guitar.com/forum/showthread.php?t=473149
Last edited by Will Lane at Feb 28, 2015,
#6
Quote by Will Lane
With the fixed bias, just make sure you are using the same type of power tube. 6L6. Preamp tubes do not require biasing.

While it happens to be correct in this instance, Fixed Bias does not mean you can plug and play with tubes. Fixed bias refers to the type of circuit used and not whether or not the amp needs to be rebiased with a tube change.

The reason you don't have to re-bias with most Peavey amps is because they are biased very cold. It is not because they're fixed bias.
#7
I just read on another forum from a Peavey rep regarding this exact amp:

"The bias is fixed, and non-adjustable. No adjustment is required when changing tubes"


Thanks, I didn't know one way or another on that amp.

And Roc is correct, Mesa does the same thing, they don't bias their amps very hot so you shouldn't have to worry about it. Amp techs will usually tell you it's best to check it anyway. The way they bias their amps at the factory is a middle of the road level so it should work fine with any tube you throw at it, but since no two sets are exactly the same it doesn't hurt a thing to go ahead and have it biased anyway or at least checked.

With Mesa, this implies with their own branded tubes, which are supposedly checked so they fall within a certain range and will work in their amps without biasing.

That said, yes, you should be able to just put the new tubes in and not worry about it.
Hmmm...I wonder what this button does...
Last edited by Paleo Pete at Mar 1, 2015,