so I just sold my peavey 6505+ combo, and the guy is having massive issues with noise from it. I never had any serious issues, but I haven't really played the amp in almost a year. I want to try and help the kid find a solution.

Anyways, the noise is a very loud, abrasive hum. It definitely isn't normal tube noise. It happens any time the amp is switched from standby, regardless of any settings, including volume or gain. The sound happens when it is played through another cab, and when the DI on the amp is used. We have tried different outlets, different rooms, different cables, and tube interchanges (swapping 1 pre-amp tube at a time, borrowing a duet of power tubes from another amp). Noting helped.

I'm really at a loss as to what could cause this. I used to play Vox AC30's, so I'm pretty familiar with tube amps, but I just cannot figure out what this is. I hope it isn't serious.

Quote by Wisthekiller
The guitar? If he's using single coils, if the pickups aren't potted correctly, bad ground, etc...?

even when the lead isn't plugged into the amp, the thing hums.

its absolutely constant regardless of any variables we've thought to manipulate.

I'm wondering if it could be an electrical component (I'm good with tube issues and biasing, not so good with caps and transformers)
lol Looks to me like i'm that kid you're speaking of... guess we both have to result to ultimate-guitar

http://www.youtube.com/watch?v=zhsBgozsIp4 Video of problem
http://soundcloud.com/howang/peavey-sadlife Recording through DI

I took a vidoe of the problem(see link below).

The buzzing appears WHEN:
-The amp is on from stand by to on....
-All knobs turned to zero
-Input jack is disconnected or connected

The buzz is NOT present when:
-The amp is off (duh)
-On standby mode
- When I disabled the pre-amp, and plugged the speakers through another head (an orange tiny terror)

-So i know for sure it's an issue from the pre-amp.
-So here I have recorded through the XLR DI and the buzzing is present as well! I have decided to take off the grill and check out the tubes:

*I am not experienced with this so my observations may not be accurate, but i'll try my best to describe it*

- The very left pre-amp tubes and very right one seems to be whiter than the others (others only has a red glow in the dark)
- when tapped with a pencil, the pre-amp tube at the far left seems to make the most noise... but just hearing it doesn't seem to be that abnormal to me...
-After swapping the tubes two at a time (with working tubes I borrowed from another amp head) the buzz is still around

Any suggestions would be greatly appreciated.
Last edited by howangcturtle at Mar 26, 2012,
I'm working from a 6505+ 112 combo schematic from 2009. I don't believe a lot has changed in these amps. So, hopefully we'll get this figured out.

Start off by pulling the first tube (V1) and turning the amp on.

Does the problem go away?

If not, put V1 back in and remove V2.

Continue this process until V4. If the problem doesn't go away with any V1-V4 removed, you have a problem in your power amp or power supply.

Let me know the results of this little test before I go on.
Do you have a copy of the schematic (the amp was purchased in 2010, so it could have been made in 2009) or a tube task chart so that he can identify the tubes positions?

also, that you for your help
K i just did it and problem is still there. i'm assuming i'm only supposed to do that with the V1- V4 tubes, which are located at the very front. Shouldn't try it with the power tubes and pre-amp tube in the middle?

PS: I tried to plug in a cable to complete the send and return circuit, somehow the buzzing cut off by about 20%
So, my guess was wrong. I thought you'd have a grounding issue at the input (which is very common).

Now we've ruled out most of the preamp. Now pull V5 which will be kinda close to the output tubes. If the buzzing stops, your problem will be either in your reverb circuit or in your effects loop circuit. Or it could actually be in the phase inverter.

Otherwise, it is a power amp problem.
Could the issue be a bad power tube or 2? the amp is pushing 2 years, and I've read that the stock tubes are pretty average.

Could that be the source? I have a couple 6l6 powered amps, so finding a matched set should be easy
Is the hum present when you plug something into the FX loop
Tastes like chicken, if chicken was a candy.
so, when he pulled the V5 out, the amp became much quieter (only normal tube noise)

any ideas?
Noise goes away after pulling V5, but SWAPPING new tubes in doesn't help (i swapped an 12AX7 from an orange tiny terror).

I also tried disconnecting the reverb tank, and the buzz is still there. When I touched one of the cable for the reverb tank it makes a huge sqeak, not sure if that's normal.
The huge squeak is normal. So, my initial thinking is there is an issue with your effects loop jacks. Most issues I've come across in PCB boards is due to an input jack with a some broken solder joints. Or the switching in the jacks may not be working properly.

Your power supply is odd. Normally I'd warn you about the danger in the high voltage circuit, but there is a bleeder resistor there to drain off the residual voltage. The heater voltage is DC, so there is some very large caps here. This will bleed off too through the tube's heater. The other power supply goes to the SS components which should sufficiently drain that power supply.

Just unplug the power cord from the wall, and let it sit for a good 30 minutes. Then you should be able to work on it. Confirm this with a voltage meter. Then simply reflow the solder joints around on the Send and Return jacks. You way also check that they are switching properly while you have them exposed.

If you don't feel comfortable doing this, consider taking it to someone you feel to be more competent. You're not working around an integral circuit of your amp, but opening and working on an amp could be a daunting task if you are unfamiliar with what is going on inside of it.
Yep. Your FX loop is always in the circuit. If the switch in the jack isn't working properly, you could get some weird hum. Since you said jumpering across helped, I believe your problem has got to be somewhere around there.
Cool, thats probably the sort of thing that is better left to an authorized repair center (the shop I bought it at closed down, but there is a repair center in town)?

is there any way to narrow it down further than that, or just take it in and explain to the tech whats been going on?
If the tech is reasonable with his bench fee, I'd just let him go through it. If it's someone that wants $50 every 20 minutes plus a $60 bench fee (besides telling him where he could kindly insert his bench fee), I'd explain to him in the fullest detail possible before letting him open it up.

Authorized repair centers are a double edged sword (I'm a Peavey authorized repair dude myself). They're great if something big goes out. Then you can just order a whole new board and not have to deal with the delicate traces that are on the PCBs. However, that also means that if it isn't under warranty, you'll have to pay Peavey's prices for that board.

Since this is a minor problem that is most likely due to some cracked solder joints, I wouldn't be too scared to take it in to your local repair shop.
Given that you're familiar with peavey's policies (I liked some of the amp designs you had on your website too, btw), would you figure this could be a warranty issue. I realize its impossible to be certain without having seen the amp, but im curious anyways (amp was purchased june 22, 2010, I have proof of purchase)
You can extend your warranty for free to five years, but it should be two years by default. It is supposed to be for the original purchaser, but usually we just look at the receipt or the serial number and go. You should be good and get it covered free since you have proof of purchase.


Just like to update everyone on what the real issue was. After comparing it to another identical 6505+, it turns out the shielding paint on my 6505 was virtually non-existant. Took a long time to track, but that was the main problem. The power tube socket was also on the recall list and was replaced. So before you buy a 6505 and thought that they're supposed to buzz like crazy when you purchase it, think twice and inquire a technician and do a few comparisons around town.

The tech was a certified peavey technician and had really great customer service. Props to him! That is all.