Triple XXX head pops, cracks, and hums. HELP

[CoopDaKill]

My Peavey Triple XXX head started making poping noise, crackleing noise a few weeks ago. Now it is also starting to hum. I am using Ruby 6L6's that are less than 4 months old, with moderate usage. I'm thinking that one of the tubes are week? The first three from the left are glowing kind of blue, but the fourth win is just orange. The preamp tubes are only 4 months old too. I've tried different bias settings, but does not help. What is the proper bias setting for me? I have read that Peavey made this amp to run the bias wide open, if you want. with no damage. I played a gig before the amp noise started, where the club was having some electrical and ground problems. Could I have had some damage then? Any help or advise will be appreciated. Thanks,
Coop

[Chuck H]

It does sound by your description like one of your power tubes could be failing. It's a simple enough matter to test the tubes themselves. You just need to find someone/someplace with a tube tester.

Shift the power tube socket positions and see if the one odd tube still looks different than the others or if the problem stays with the same socket. That could help narrow down the problem. If the problem stays with the socket it could be a bias feed resistor, a screen grid resistor or just a dirty tube socket. If it's a dirty socket the problem may go away temporarily when you swap the tubes around. Try holding the tube in that socket (with a pot holder or cotton cloth) and rocking it gently in a rotating motion. If you hear cracks, pops and intermittant humming try cleaning the socket.

If the problem follows the tube, that is, the same tube that looks different now still looks different in another socket, pull it and one other tube. If the suspect tube is in the inner pair, pull the two inner tubes (2 and 3). If it's in the outer pair pull the two outer tubes (1 and 4). Then set your impedance selector for half the impedance it's set to now (if the impedance is set for 8 ohms change it to 4, if it's set for 16 ohms change it to 8). Now play the amp. Did the problem go away??? Now exchange the two tubes that are in the amp for the two you pulled, still only two tubes in the amp. Did the problem return??? If it goes like this, replace the tubes.

Chuck

[Enzo]

Don't even need a tube tester. Pull that odd power tube out of the amp and try the amp with only 3 power tubes.

If the noises go away, it was a bad tube.

Tubes can fail at any time, new or old. I'd be betting on a bad power tube.

if you need to, you can remove each tube one at a time and try with the remaining three. FOur tries and you have tested the amp without each tube. if one is bad, the amp should act different when it is out.

The bias on these is not critical, set it to the middle for now. Once all your issues are sorted out, then you can fiddle with it. Set it by ear.

[CoopDaKill]

Thanks for the help guys (Enzo & Chuck)... I moved around the power tubes and the popping/crackling noise seems to have gone away, but the amp just does not have the volume that it used to. It's loud, just not as loud as it used to be or should be. No where near my 5150 head. I opened up the XXX and noticed that one of the two big round caps has the plastic coming off of it. It doesn't look like it's leaking, but I am curious if this could be part of the problem. Also I check it out in the dark and seen no arcing at all. I did notice that when I twist the 1 12ax7 preamp tube, I did hear a little noise. I am pretty sure some new power tubes would help, but I want to make sure there are no other issues first. Any help and advise would be greatly appreciated. Thanks. Coop

[Enzo]

You still have not determined if all your power tubes are working.

Moving them around is fine and may refresh funky socket contact, but it won't restore a dead tube.

Sit down with the amp and take the back off. Pull all four power tubes. Now put ONE tube in the end socket and fire up the amp. Sound may not be perfect, and power will be reduced, but it should work. Now pull that tube and try the next in the same socket. Sound about the same? Now try #3, then try #4. If they all work about the same, then they are probably all OK. If one acts different from the others, then it is likely bad.

If no tube worked in that socket, then the amp has a problem.

OK, now we know if we have a bad tube. But we still don;t know about the amp. Assuming that first socket worked, empty it again. Now take one of the tubes we know works and plug it into socket #2. Does that work about the same as the first socket? We don;t have to try multiple tubes, we already know which ones are good or bad. Then move the tube to socket #3, and finally to socket #4. Do any of the sockets sound different from the others?

I am not looking for some tiny difference or subtle change. I am looking for any night and day differences. If one socket just works completely different from the others, it has a problem. If the same tube sounds the same in all four sockets, then they are probably OK.

There you go, a poor man's tube tester. You should now know if all four tubes are good and if all four sockets work.

[CoopDaKill]

Thanks Enzo. You are the man. I will do the tube test later today and let you know the results. Can you give me your opinion on that big cap that has the plastic covering coming off of it? Is it a sign of a problem? Thanks Again.

[Enzo]

Probably fine. Slice away the plastic and look at the actual metal cap body underneath. if that is still flat, the cap is fine, the plastic just warped from heat. If the cap body is bulged, then it is bad.

[CoopDaKill]

Tube Test Results. Hi Enzo. I done the poor mans tube test exactly as you instructed. All tubes performed good. What I discovered was that the #2 socket, did NOT work (from the right, looking at the back of the amp). I could only hear a very faint signal and it was real crackly sounding. All 3 other sockets had pretty good volume and sounded the same. What does this mean? How can I fix it? Is the socket bad? Thank You for your help, advise, and knowledge. Mike

[pecorporation]

Enzo, I like your poor mans tube tester! I learn something new everyday here.

[CoopDaKill]

Open Screen Resistor ????

I talked to Gene at Peavey today. He said it sounds like an open screen resistor. I'll try to find some resistors and replace them. Let me know what you think. Nothing seems loose on the power board, so I hope this is the problem. Thanks for your help. I have really learned a lot from this great forum. Mike

[CoopDaKill]

Problem Solved - Peavey Triple X Head

I replaced the suspected open (bad) screen resistor and problem solved. The volume is back to what it should be and the popping and crackling noise is gone. This amp will melt your face, now. If anyone else has this same problem, just follow the instructions on Enzo's Poor Man's Tube Test, to find out if you have a bad power tube and/or a non-working power tube socket. The screen resistor for this amp is: 100 ohm/5 watt/wire wound/Axial leads (Cement- long white rectangular shape) power resistor. 5% - 10% tolerance. The XXX had 10% tolerance resistors, but I was told that 5% is probally even better. Tolerance is not a critical factor. Thanks to everyone,Gene at Peavey, Chuck, Music Electronics Forum and especially, Enzo. I am eternally grateful for all the help and knowledge. Rock On.

[CharlieP]

Just remember that the poor man's method won't work on an amp with heaters wired in series. XXX works fine tho!