#1
My amp has had a very noticeable decrease in decibel level. It's literally a 1/10th as loud as it should be for a peavey 6505. I plug my guitar directly into the amp and still having this problem, so I know it's not any gear or guitar problems. The pre-amp and post-amp pots are working fine. The power tubes look okay. Any ideas on how to troubleshoot this before taking it in for amp service?
#3
311 has the right advice. As a side note, you really can't look at tubes and determine their condition. The only time that works is when the getter has turned white due to an air leak in the glass envelope. A tube with weak emissions will still look like a brand new tube from the box, at least to the naked eye.

As already suggested, replace your power tubes and obtain some spare preamp tubes. FWIW, preamp tubes will typically last a lot longer than power tubes, since they're not driven as hard.
#4
Quote by KG6_Steven
311 has the right advice. As a side note, you really can't look at tubes and determine their condition. The only time that works is when the getter has turned white due to an air leak in the glass envelope. A tube with weak emissions will still look like a brand new tube from the box, at least to the naked eye.

As already suggested, replace your power tubes and obtain some spare preamp tubes. FWIW, preamp tubes will typically last a lot longer than power tubes, since they're not driven as hard.


+1 to everything, but if you ever see red-plating, turn it off and throw them out, that is probably the only visible way to see if a tube is bad. shy of that, they will light up fine, but won't fully function.
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#5
Ah thanks for the replies. So I suppose it's unfortunate power tubes are not like a lightbulb where you can obviously tell if it's wasted.

They were last replaced 6 months ago and I probably have been using my amp every other day since then. I have only had the amp a year. Is it a crap shoot as to how long they last? How much to expect to spend for replacements?
#6
311 is almost certainly correct but try this first anyway.
Pull out a tube. Spray some contact cleaner (NOT WD40) liberally onto the tube pins and work it in and out of socket a few times. You are using the tube as an applicator. Plug it back in and do the same to all the rest.
Often it's just filth and/or corrosion causing a bad contact. You'd be amazed how many things can be fixed just by pulling them apart and cleaning them. Not that a guy in a shop will tell you that. He'll replace something (or say he did) just to justify the cost of the labor.
If you can do it yourself, do it. Try cleaning it, then do what 311 said.
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#7
Yeah. Cathbard is right. That is almost ALWAYS a good first step when trouble-shooting an amp. Get some Dioxit contact cleaner and spray it on all the pins one at a time like Cathbard is saying.





6 months doesn't seem like a very long time. What is in there now? Which 6505 do you have and is it new or used?
#8
yep. and if you like the tubes that were in there, then if you get the same brand sgain you dont have to re-bias. just get a matched quad.

if this kind of thing keeps happening, you either are playing so much then that is just the way it is, or your amp needs a proper rebias and setup cause it may be over-working tubes.
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#9
^ Not particularly bad advice ikey, but I do disagree somewhat.

6 months is VERY short life for power tubes. Even playing every day he should get a good 2-3 years out of decently made tubes. Also, power tubes really don't factor in as far as the tone of the amp. Preamp tubes? Sure. Power tubes? Not so much.

Therefore, unless someone is willing to spend over $100 on power tubes by getting something like SED =C= the best option these days really is JJs for that 'perfect' price:quality ratio.

Chinese (most Chinese) tubes are kind of shitty, Ruby and Mesa are rebranded (as are many others), and Sovtek are kind of mediocre.

Also, the 6505 doesn't really have a useable bias sweep and needs to be modded to get any real benefit from a rebias. Peavey biases their amps cold so I doubt the tubes are being over-worked. Again, not saying you are wrong there - that could very well be the case. If it is, I would expect their to be some other issue with the amp that is causing the tubes to run not like possibly a bad grid resistor or something like that. I'm not an amp tech. Peace.
#10
I'll give the cleaner suggestion a try, Thanks!

6 months is not a long time at all. This is not my first tube amp. In fact, the first tube amp that I have is 3 years old, and I have never once had to change the power tubes in it.

I bought my 6505+ last year. Brand new. After a couple of months, the power tubes went out and it blew a fuse. I took it in for service under warranty. Then a couple of months pass and it blew another fuse. Took it in for service yet again. The amp repair shop is very reputable and they have worked with some professional guitarists - you have probably heard their names.

Now I have a significant loss decibel quality and hate to take it in for the third time, and wanted to know what most people would do in my case. I hate being ignorant to how my amp works so wonder if there is a quick fix.
#11
Hmmmm. That is why I'm asking. Is this the Chinese made 112
Or the US made one?

Either way it seems to me that this amp DOES have issues - despite how great
The amp and your techs may be.

Contact cleaner
New tubes
Bias mod
#12
Quote by 311ZOSOVHJH
Hmmmm. That is why I'm asking. Is this the Chinese made 112
Or the US made one?

Either way it seems to me that this amp DOES have issues - despite how great
The amp and your techs may be.

Contact cleaner
New tubes
Bias mod


I do know its the Chinese one. After the fact... aren't they all.Chinese made now? I was worried I purchased a lemon. I would rather get a brand new one but I don't know if warranty allows it. What is the bias mod?
#13
The only Chinese made 5150/6505 is the newest 112 combo.

The rest are US made.

The price new reflects that.

If it is still under warranty then exercise that.

I would demand a new one.

Bias mod adds a greater sweep by replacing the bias potentiometer that makes it actually useful.
Last edited by 311ZOSOVHJH at Nov 28, 2013,
#14
okay well if new tubes and a bias wont fix it, then there is something structurally wrong with the amp. but techinally i can see a professional artist playing so much they burn tubes out every 6 months between practice at home, studio, live play. etc.

for the average guy i agree thats WAY too short, even for a gigging musician.
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#15
Yea I don't play it THAT often. Well, damn, looks like I hope I can get a new one. I hope Peavey will allow me to exchange after 2 repairs already in a <1 yr period and yet another. I don't know how common lemons are with these Chinese Peavey's but looks like it's not too out of the ordinary.

The tubes were replaced with JJ 6L6 by the amp service techs. They have a fantastic reputation so I trust them. I think there is something inherently wrong with the amp from the factory.
Last edited by sweetdude3000 at Nov 28, 2013,
#16
Quote by sweetdude3000
Yea I don't play it THAT often. Well, damn, looks like I hope I can get a new one. I hope Peavey will allow me to exchange after 2 repairs already in a <1 yr period and yet another. I don't know how common lemons are with these Chinese Peavey's but looks like it's not too out of the ordinary.

The tubes were replaced with JJ 6L6 by the amp service techs. They have a fantastic reputation so I trust them. I think there is something inherently wrong with the amp from the factory.


Which amp? The 112 or the the head?

Only the head has a bias adjustment. You basically turn it up all the way.

Sometimes when a power tube dies it takes part of the power tube circuit with it. It can damage resistors, sometimes it may not be so noticeable. Worst case would be a resistor that drifts with heat as it can be sneaky to detect.

Do you have the service history of what they replaced when the fuses blew?
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#17
I had a screen resistor fail with a power tube a few months ago. That's why it's smart to replace the power tubes when they start to warn you of imminent failure and not after they actually go tits up.
So pursuant to this thread. If cleaning doesn't solve it completely, replace them asap.
As for which; SED =C if you can afford them, JJ if you can't.


As for the bias control on those. The full sweep is in a safe range so just adjust it by ear. You'll probably want to turn it all the way up, but just trust your ears. That is of course if it in original trim. If it's used it may have been modded by the previous owner. Modding for more adjustment is a very common mod.
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Last edited by Cathbard at Nov 28, 2013,