Awful Breakup Noise, could this be power tubes?

[ryanf]

I have a 50 watt SLO Clone (El-34), and when I turn it up to a certain volume, and pick hard, it makes an awful clipping noise. there is a huge volume jump when this happens. I am fairly sure it is not in the preamp, as it does this when I go through the FX return. I dropped a power tube onto a concrete floor without it breaking, so I am thinking that this may be the problem.

I'll try and scope it out when I get some time, but I was just wondering if this could be the problem.

[ThePRNDL]

Tubes are the first thing to check, and dropping them isn't good.

The next suspect is electrolytic caps in the power supply. Sometimes they can do this when beginning to fail.

I've also found coupling caps to do this, but that's fairly rare.

[mat]

On my case it was one of the main filter caps: https://tubeamparchive.com/viewtopic.ph ... highlight=

[mat]

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[mat]

deleted triple post

[Bob-I]

I have a 50 watt SLO Clone (El-34), and when I turn it up to a certain volume, and pick hard, it makes an awful clipping noise. there is a huge volume jump when this happens. I am fairly sure it is not in the preamp, as it does this when I go through the FX return. I dropped a power tube onto a concrete floor without it breaking, so I am thinking that this may be the problem.

I'll try and scope it out when I get some time, but I was just wondering if this could be the problem.

It could be bias also. Crossover distortion sounds like you describe. Make sure the bias is in the area of 60-70% total dissipation.

[ryanf]

When one El-34 is running at .04 A the other is at .03 A. They were supposed to have been matched, and I dont remember them being this drastically different before.

Is this indicative of a broken tube, or could mismatched tubes do this?

[Chicken Head Red]

I have a 50 watt SLO Clone (El-34), and when I turn it up to a certain volume, and pick hard, it makes an awful clipping noise. there is a huge volume jump when this happens. I am fairly sure it is not in the preamp, as it does this when I go through the FX return. I dropped a power tube onto a concrete floor without it breaking, so I am thinking that this may be the problem.

I'll try and scope it out when I get some time, but I was just wondering if this could be the problem.

Problem?! You have to teach the rest of us how to drop a power tube on a concrete floor without breaking it! ':shock:'
Here's a trick I was reminded of this week after replacing damn near every component in an SE design trying to eliminate what sounds like perhaps a similar problem. Remove the chassis from the cab, place it on your well lighted workbench, turn it on, plug in you guitar, then, TURN OFF ALL YOUR LIGHTS! Now bash your guitar and look for the spark in the dark. I could've saved myself hours of time had I remembered this trick when I started. Maybe I can save you some
Good Luck

[Structo]

Arcing socket?

[ryanf]

Well, I replaced the power tubes, and discovered that between the cathode follower and the master volume that the wave is clipping abnormally. I noticed this occuring across the treble capacitor, so I replaced it. Although it looks better across this particular cap, the breakup noise still occurs. I can make it happen by putting a signal in through the effects in and turning up the master volume. Its a distorted wave with an infinite slope. I will do some more testing later, when my frustration dies down.

[drz400]

Well, I replaced the power tubes, and discovered that between the cathode follower and the master volume that the wave is clipping abnormally. I noticed this occuring across the treble capacitor, so I replaced it. Although it looks better across this particular cap, the breakup noise still occurs. I can make it happen by putting a signal in through the effects in and turning up the master volume. Its a distorted wave with an infinite slope. I will do some more testing later, when my frustration dies down.

Put 1 ohm 3W 1% resistors from pin 8 to ground, measure across them, also measure across the screen resistor. IF the power tubes are good
SLO does not have symetrical clipping and to look at a sine wave going into a SLO effects return without getting the ramp looking waveform you must turns bass on 10 and all other tone controls on 0 and careful how much input level you hit it with.
What layout did you use? Layout is very important in high gain amps, did you put all series grid resistors right at the socket pins? I know the amps well and have owned a few over the years if you want to send me the schematic / layout you used I'll look it over.

Sounds like you have blocking distortion, cause by layout or a missed component.

[drz400]

double post cant find the delete button

[ryanf]

I used the schematic and layout here (click on slo docs): http://homepage.mac.com/WebObjects/File ... US&lang=en

For the power tubes, the screen and grid resistors are on the tube. For the others, they are on the board. The clipping isnt normal. After the master volume, as it is turned up there is a dip in the peak, and it goes wild when you turn it up. I'll try and get some shots of the scope or maybe a video if that helps.

I appreciate it,

-Ryan

[drz400]

It will take me the weekend to go through the documents, certainly not a SLO layout, do you know others using this same layout with no issues?

One problem , any grid stopppers should really be right on the socket or you could be picking up some bad osciallations and freak out, they also wont do their job. R8 and R21 need to be moved right at the pin of the tube, I'm sure Soldano would tell you this. If this doesnt fix it disconnect the clean channel altogether and double check all grids have a ground reference and you havent missed anything, you presence control works correctly ? it doesnt affect the noise right? Just a long shot you have the primary not reversed. Definately moe the grid resistors to the sockets first, also are you using shielded cable where needed?

Any pictures of the actual build? Remember with high gain circuits layout and using shielded cable where needed is critical

[ryanf]

Yes others have used this layout with good results. The noise is occurring in the power stage, as it happens when I plug into the effects return, and the signal coming from the preamp sounds fine. Other than the breakup, the amp is quiet. There was a time when it was working and sounded fine. Shielded cable was used where needed. Presence and depth seem to be working, but they arent very apparent with the awful noise.

What do you mean about the primary? I did get an awful squealing sound until I reversed the leads of the OT primaries.