Other Amps

Buzzing from Vibrolux Reverb

1

I've got a '65 Vibrolux Reverb that when played loud buzzes. It sounds like a vibration. At a certain point when the sound level drops the noise goes away. I've played it through an external cab and also replaced the original speakers and the same thing happens. Is it possible that a component in the chassis could be vibrating through the circuit? I will retube the amp later today; all current tubes test okay in my Orange VT1000 (tube tester for dummies!)

2

I had a musicman 12" for repair that did that. Hard to find rattle. I put a piece of foam beneath the transformer and chassis an that solved it. It's a challenge

3

Thanks - that's why I tried an external speaker cab. I have to spend more time with it, maybe try some different tubes first.

4

Here’s a gratuitous amp photo:

5

Take the chassis out of the cab, flip it over and stand it on a work top. Reconnect the speaker cord and try the amp.

You'll soon find out if it's the amp or the cab or just when the two are fitted together. If you are still not sure and have another amp then connect the amp's speaker cord to the other amp's speaker. That'll nail it down.

6

Every time I build a new combo amp, the first thing I do is chase cabinet rattles. You can quickly differentiate cabinet noise from circuit/microphonic noise by listening closely to the speaker. If it’s comming thru the speaker it’s the amp. Remove the grille. It’s held on by four pieces of Velcro and can often rattle.

Since you’ve tried an external speaker, it’s likely not the cab. With the amp off, lightly tap on each power tube and the rectifier tube. If you hear a jingling sound that’s where I would start. If it’s a tube, you can buy silicone rubbers to try and dampen the microphonics.

Very cool amp by the way!

7

After tapping on each tube, if you're comfortable exposing the chassis with the power connected without shocking yourself, tap on each resistor and soldered connection with a chopstick.

8

You can also check the spider of the speaker for stray nuts and bolts etc. this can be very noisy.

9

Going to a tech, I don't have time to really dig in right now. Hopefully just some dirty tube sockets or a bad solder joint allowing for some vibration. It's a black panel amp so no Velcro on grill. The same noise with different speakers installed in the combo cab and also with just an external cab.

10

Very possibly tube related. The tube itself or the socket needs to be cleaned and tensioned.

11

If it was hardware I would suggest try holding or moving the tilt-back legs.

12

Tighten all of the screws that hold the baffle board in. They loosen over time. No velcro present on a '65, but the Silverface amps had it.

13

It's very possibly oscillation from bad filter caps, especially if it does it more on low notes. I had exactly that issue with a Blues Jr. and a cap job solved it instantly.


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