Can I do this with an oscilloscope?

[UsableThought]

After removing every little bit of crackling in the amp due to very small connection issue like imperfect tube socket fit, I was left with only the low frequency distortion/buzzing being created by the amount the V2 tube was being driven past it's optimum curve. This is evidently inherent in the original Fender Deluxe Reverb AB763 circuit design.

Your logic would require that every Fender amp of this design sound the same as that very unpleasant sound clip. They don't. Beyond that, in terms of what a triode at V2 in pretty much any normally operating guitar amp sounds like when it is overdriven, it is nothing like the noise in the clip. "Low frequency distortion/buzzing" as you describe it represents something abnormal going on. That you have failed to find the problem doesn't mean there isn't one.

Rather than try to attempt to apply logic as you have done, only to arrive at an incorrect conclusion, my last suggestion is that you find a good amp repair shop. I'm going to uninvolve myself from further participation as I have not been helpful.

 

[dlgoff]

I'm going to uninvolve myself from further participation as I have not been helpful.

I, for one, have learned from you. Your involvement, I'm sure, has/will help others.

 

[Planobilly]

Sorry guys, I have been away for a couple of days playing guitar and fishing.

Evidently, I was very unclear in my assessment statement. The original fault depicted in the in the audio portion of the video was resolved by replacing the tube socket.

The additional low frequency distortion/buzzing I alluded to is most likely consistent with the design. I say this because the sound I am unhappy with, produced at the plate of V2B, does not occur at the grid of V2B. This "sound" is, I assume normal.

The amp is working "normally" now as far as I can tell. It was played by another guitar player in the band I play in and he thought the amp sounded fine.

It was never my intent to make a "reproduction" of a vintage AB763 Fender Deluxe Blackface or have it sound like one. I own a 1966 original Fender Deluxe Reverb that is completely original except for new filter caps and tubes that have been changed over the years.

The amp that I built is purely an experimental amp. It has given me an inordinate amount of problems due to new components that have failed, whatever the cause of those component failures were.

So...back to the original intent and questions of this thread. I am sure there must be ways to better utilize the scope I own and I obviously need to become better educated in it's use . There is a possibility of using the recording software I have. The filters Jim linked look like a very good idea so the concept I ask about is valid.

I actually found the fault by disconnecting things and listening to individual stages using an audio probe I built. This has been a good exercise in identifying a hard to find fault that did not respond to normal methods. Finding a bad tube socket is normally pretty easy to do. Having a bad tube socket produce this sort of fault is something new to me. Having said that tube amps are world famous for doing strange things.

Anyway, thanks to all of you for the help and education.

Best wishes for the new year,

Billy

 

[dlgoff]

So...back to the original intent and questions of this thread. I am sure there must be ways to better utilize the scope I own and I obviously need to become better educated in it's use .

I actually found the fault by disconnecting things and listening to individual stages using an audio probe I built.

Aren't ear great instruments?
Remember me writing in your original Building a vacuum tube amp from scratch thread ...

I wouldn't have taken on a tube circuit that big; solid state maybe. I've built several solid state audio circuits by just using a VOM and my ear.

bold by me

 

[Planobilly]

"Ears" are certainly easier to use and interpret in a lot of cases.

I find it difficult at times to relate what I see to what I am likely to hear. This is an example of a component change which will change a sound. I find it hard to look at the graph and have a really good idea of what I am likely the hear.

Oscilloscopes seem to be pretty hard to use to display distortion in the audio frequencies. I guess there are high quality scopes that are easier to use than the one I have. For one thing, there is a very limited or no description of some of the FFT functions in the user's manual for my scope.

This whole amp project has been more difficult than normal due to the fact I built everything from the chassis to the wooden case and did the Tolex covering.
I assume I posted a photo of the finished amp somewhere but here it is just in case.

Cheers,

Billy