Bazaar combo problem: Resolved

[Bob-I]

I don't think there's a solution, and that's not why I'm posting, just sharing.

I have this little Dumble like amp I built in a Princeton chassis and I built a head cab. I saw a 1x10 SS Fender amp on Ebay broken for $25 so I figured a 1x10 combo would be easy to carry around and sound decent.

I put the chassis in, perfect fit, but the stock speaker was damaged. I finally got around to breaking in and installing a Celestion Tube 10. It's still breaking up, not in a good way, like a voice coil rub in one specific frequency, maybe also like crossover distortion.

I checked the bias and yes, it was way low so I adjusted, plugged in the cab with the chassis still out, perfect.

Installed the chassis, nasty noise back. Hmm... maybe the speaker IS bad so I swapped it out with a Weber 10S I have lying around. Same thing.

Took the baffle out, no problem, back in, problem.

Took the chassis out, no problem, put the chassis in, problem.

Here's the REALLY bazaar thing. I recorded a clip with my iPod/Protrack. YOU CAN BARELY HEAR THE PROBLEM. Give a listen. There's a few seconds with the problem, a few seconds without, then a few seconds with again.

I'm thinking the power tubes are too close to the speaker, maybe 1" clearance so there's most likely no solution.

The head is back in the head cab for now.

[briane]

How many watts is it?

I ask, cause I have combos with tubes almost literally touching the speaker, no issues. Those are 25 watters or less though.

I really doubt its due to tubes too close to the speaker. What that does cause is tubes to shake around when played, and thus the tubes have a shorter life.

[Bob-I]

How many watts is it?

I ask, cause I have combos with tubes almost literally touching the speaker, no issues. Those are 25 watters or less though.

I really doubt its due to tubes too close to the speaker. What that does cause is tubes to shake around when played, and thus the tubes have a shorter life.

It's like 15 watts. I retensioned the tube sockets as well.

[JimiB]

did you try with different power tubes? Sounds like a tube to me - could be pre or power but the vibration of the speaker can do this as mentioned above.

[Structo]

How close are the transformers to the speaker?

Maybe there is some cross talk going on there.

[Bob-I]

Well, I have a gig tomorrow afternoon so it's in the head cab for now. I didn't think about tubes but dummy me, I forgot rule #2

Rule #1) 95% of amp problems are because the user has no clue how to use the amp.

Rule #2) 95% of the remaining 5% are tube problems.

Since I tried all the knobby things I can forget about rule #1 so it may be rule #2. Funny that it works perfectly even sitting on top of a speaker cab. Maybe I'll be able to check it out Sunday.

[Bob-I]

How close are the transformers to the speaker?

Maybe there is some cross talk going on there.

I don't think so. They're like 3-4" away.

[heisthl]

I've built 50 watt amps with both transformers and both tubes touching some part of the speaker with no issues. That is probably not your problem.

[Bob-I]

I've built 50 watt amps with both transformers and both tubes touching some part of the speaker with no issues. That is probably not your problem.

I have too, which just makes this more bazaar. The wierd thing is I can sit the baffle in the cab and at whisper levels the problem happens, take it out and I can dime it with no problem, same speaker, happens with multiple speakers.

[talbany]

I myself have built amps where the tubes are almost touching the speaker with no issues.. It would take a speaker with a pretty high gauss rating to effect the electron flow..


Tony VVT

[Bob-I]

Thx everyone for keeping me on this problem. It turned out to be an intermittant treble pot

I put the amp back into the cabinet and tried 4 different speakers. I can't get the problem to occur again after replaing the pot. The best sounding speaker so far is a cheep Pyle. The cone had a tear that I fixed with tissue paper and wood glue, and it's got an aluminum dust cap. It sound richer and deeper than a Celestion tube 10, Jensen C10Q and a Weber 10S. Go figure.

Now I have a Princeton sized Dumble for small gigs and practices.

[Blindog]

Glad you got it fixed Bob. Sounds like a cool amp. I'd like to try something like that myself.

I was curious as to what led you to the the treble pot to be bad.

Thanks for posting your problem, this stuff is interesting.

Mark

[Bob-I]

Glad you got it fixed Bob. Sounds like a cool amp. I'd like to try something like that myself.

This is most likely the original D-Lite. Norm and Moss were impressed at my little bitty amp so they decided to build a minimul Dumble.

I don't usually like 10" speakers but I figured if a Princeton can sound good, so can this one.

I was curious as to what led you to the the treble pot to be bad.

When folks said that the speaker shouldn't interfere I replaced the tubes, then when that didn't fix it I started chopsticking. Moving the treble pot lugs caused the noise, bingo.

[heisthl]

If you make them small enough you don't need a car to get to the job:

[Bob-I]

If you make them small enough you don't need a car to get to the job:

I figure when I'm heading to the gig I can just put it in my pocket with my house keys and picks.