Delta Blues 2-10" problem

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pdivs
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Delta Blues 2-10" problem

Post by pdivs » Wed Sep 07, 2022 6:22 pm

Hi folks,

I'm getting quite a bit of distortion (the bad kind) at all volume levels. I've narrowed the problem down to when I turn the bass past 2. I've tried different speakers and both do it so I'm assuming the problem is a tube or interior electronic problem. Anyone ever experience this and/or have any ideas where to start?

Thanks

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JamesPaul
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Re: Delta Blues 2-10" problem

Post by JamesPaul » Fri Sep 09, 2022 10:30 pm

It could be a microphonic tube. They do not all sound the same. You could try the chopstick/pencil eraser test, but they are not always 100%. Usually when a control is linked to the issue, it will be a tube in front of, or in, that control circuit. The DB is like a C30, so the tone stack should be after V2.

Anymore, I just take a spare preamp tube and substitute it in to test.

Swap V1 out for your spare pre tube. Does the distortion issue still occur? If not, toss the old V1.

If it still occurs, put the old V1 back in and swap your spare with V2. Still have the distortion issue?

Same for V3. Still there?

My EL84s usually go dull/lifeless before they develop any issues. I swap them and V3 at that time. Since you are already swapping, you can try the EL84s. If your EL84s have some time on them, I would just swap the entire set. If they are relatively new, try swapping a spare in V4 through V7. I give some cool down time if I am doing this with power tubes; cool to the touch.

If the distortion issue is still there, it likely is circuit related. You may be able to help your tech with a little more testing.

Does it occur on both channels?

Is it truly not distorting at any volume level when the bass is below 2?

Does activating the Boost make any difference? The Boost on the C30 and DB actually removes part of the tone stack from the signal path.

That is about all I can think of for now.

If you do find it is a tube, please let us know which one it was. Bass above 2 is a relatively specific condition.
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
James Paul's Peaveys
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