What sounds like a blown speaker but isn't a blown speaker? - Fixed!

[Mapleneck]

Got 4 sets of speakers and they all do the same thing (rather suddenly) in my old Vibrolux. Rattles like a blown speaker, especially on low notes. This isn't the ordinary Fender fart out. It sounds blown. But the speakers are fine, in fact there is an attenuator in line (a Dr Z Brake Lite). (Assuming its not the attenuator) Will a fried tranny or output tubes sound like that? Tell me where to look and I'll start debugging. Thanks

[Jimmy P]

I know you said assuming its not, but did you try bypassing the attenuator for a minute or two?

[WaltC]

bad solder joint(s) in the circuit, bad solder joint on one of the several speaker connecting plugs between the amp, the attenuator and the speakers, bad jack or plug on one of the wires, just to start...

[Tone Meister]

In addition to the ideas above, try swapping the phase inverter tube. Yours could be oscillating.

[Blue Strat]

Originally Posted by Tone Meister

In addition to the ideas above, try swapping the phase inverter tube. Yours could be oscillating.

...or one half could be bad.

Since we don't know what you're hearing...it could be ANYTHING. Definitely take the attenuator out. Run to an extension cab for confirmation.

[Faraldi]

Does the issue happen right away or is it after the amp has been on for a while?

I had issues with bad solder joints with two big electrolytic capacitors on a Deluxe 90. Made a real farty sound when it warmed up.

[Jerry Glass]

Loose internals in a power tube can sound like a blown speaker.

[Mapleneck]

Awesome, I knew you guys would come through for me. I needed a laundry list of things to check and I have a good start on one here. It will be the weekend probably before I dig into it, but I was going to yank the Brake Lite. I know the speaker clips are flimsy, one broke off the other day at a gig, and I had to hurriedly solder the clip back on to the wire (I hate soldering wires to the speaker) just to finish the night. I have some spare tubes to switch in.

The problem happens immediately, and worse on lower loud notes. Just like a blown speaker. And it seems to come from both speakers equally. Really annoying sound. As long as it is something easy like a speaker spade, wire, solder, tube etc, and not a transformer or something, then I am golden. I'll eventually weed it out. Just wanted to shave a little time by picking TGP brains first. I'm a single dad (x3). Time is what I don't have! Thanks to all for your input!

[Ronsonic]

Tubes, filter caps, it's pretty much, start going through the amp and fixing whatever you find time.

[mark norwine]

What sounds like a blown speaker but isn't a blown speaker?

Blocking distortion.

[Pete Cage]

Is it a Vibrolux Reverb?

[Mapleneck]

Originally Posted by Pete Cage

Is it a Vibrolux Reverb?

Yes. 1970.

[Mapleneck]

Originally Posted by mark norwine

What sounds like a blown speaker but isn't a blown speaker?

Blocking distortion.

Any common causes?

[Pete Cage]

Something easy to try: Pull out V3 (12AT7 reverb driver tube) and see if the problem goes away.

[Mapleneck]

Originally Posted by Pete Cage

Something easy to try: Pull out V3 (12AT7 reverb driver tube) and see if the problem goes away.

Awesome, I'll try that tonight. Will that indicate a problem in the circuit or the tube or inconclusive? In case I didn't describe it well, this is a very high freq crackle, that gets worse with louder lower notes. Just like a couple blown speakers I have heard. Dang I wish I could make clips.

I did run home at lunch to let the dog out, and I checked the speaker spades. Even the one I performed emergency surgery on the other night seems sound. Peaked under the "F" cap, and everything seemed well connected.