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Post subject: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 2:50 am
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I've had my 68 Custom Vibrolux Reverb for a couple of years now and I absolutely love it. I bought it new and I've gigged with, recorded with it and it keeps getting and better, especially now that the speakers have seen some miles.

I recently discovered a rattle noise when I hit certain frequencies. It is not a string buzz noise, but reminiscent of a lose piece of metal vibrating. I've had a look at the back but I can't see any obvious source for the noise. Strangely it only happens on certain frequencies - the A note seem to accentuate it (especially low A).
This comes through when I play clean and I am not sure I am not imagining that the noise increases with volume.

Any thoughts / tips / suggestions?


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 3:25 am
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You may have fried a speaker. Try disconnecting them one at a time and see if the symptom persists. If both speakers produce the same noise, try connecting an alternate cab to the amp in lieu of the internal speakers.

Another possible source of the problem could be a loose screw -- either a speaker stud or a mounting fastener for one of the amp's transformers.

Finally, it's possible that one or more of the tubes has become microphonic. With the amp on and the volume control somewhere north of zero, try gently tapping each bottle with a chop stick, popsicle stick, or other non-conductive probe. Any tube that produces an audible "tink" when tapped is probably ready for replacement.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 3:48 am
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Thank you very much for this Arjay
I will carry out these tests tonight and report back. I definitely know there is no loose screw connecting the speakers, but i will have to check the others avenues you suggested.


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 6:36 am
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Don't tight too much speaker screws, neither other screw.

Noise ; check you guitar carefully . Something may move in your room . Tubes ?

Follow Retroverbial advice and try another speaker cab.


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 9:58 am
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I had this exact same problem with my DRRI and traced it to a faulty power tube.


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 4:07 pm
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So I've run all the tests suggested. Neither one revealed a cause.
I disconnected each speaker - on by one - still rattle.

Then checked the tubes. Still rattle. All screws are in place.

The rattle comes from the top left hand side (looking at the back the amp) - from the area of where the power tubes are. Yet, there is nothing that is loose in that area. The tubes themselves are fine. I took them out - one by one - still rattle.

It only happens on specific notes - i.e. a particular frequency. All other notes don't cause any rattle. I checked the guitar for some fret buzz but the noise is definitely coming from the amp.

I would normally not get too fussed about this sort of noise, but this one is really annoying when playing clean and I fear it may ruin recordings if left unsolved.


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 4:12 pm
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I still suspect a microphonic power tube (the chopstick test is not necessarily definitive). Do you have an alternate pair of 6L6's to try?

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 4:29 pm
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Retroverbial wrote:
I still suspect a microphonic power tube (the chopstick test is not necessarily definitive). Do you have an alternate pair of 6L6's to try?

Arjay


Unfortunately not


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 4:37 pm
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As I said before, I had this same problem with my DRRI only in my case the offending note was B, specifically on the 5th and 6th strings.

Try tapping the tubes with the eraser end of a pencil or the flat of your finger nail. If one of the tubes is microphonic it will sound very different to the good tube(s). I can't remember if the amp needs to be switched on for this test to work so try it both on and off.


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 4:45 pm
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tremolo arm wrote:
Retroverbial wrote:
I still suspect a microphonic power tube (the chopstick test is not necessarily definitive). Do you have an alternate pair of 6L6's to try?

Arjay


Unfortunately not


You have this amp since couple years , a new set of 6L6 is not a big expense.


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Thu Feb 18, 2016 4:57 pm
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The "tap test" is best done with a wooden chopstick or nail orange stick and must be done with the amp powered up and read to play. A fingernail invites a painful burn around power tubes (the larger ones), not nearly as bad from preamp (small) tubes.


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Fri Feb 19, 2016 8:12 am
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Sounds like swapping tubes is the only way to be certain.
Should I go for the same type/brand or has anyone any experience with tubes which make the tone better (though I realise "better" is a subjective word in this context)?
I noticed Groove offer several types of 6L6s...


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Fri Feb 19, 2016 9:22 am
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You can pull one power tube at a time. It won't hurt the amp. It will sound funny.
It will reveal differences between the power tubes if only one rattles.


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Fri Feb 19, 2016 11:01 am
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TimsAudio wrote:
You can pull one power tube at a time. It won't hurt the amp. It will sound funny.
It will reveal differences between the power tubes if only one rattles.


I don't want to doubt what are you saying, but I've heard that by removing one power tube you're bound to unbalance the primary side load the tubes place on the transformer, and it will leave one side of the primary completely unloaded thus putting te transformers at risk.

Is that not applicable to the 68 CVR?


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Post subject: Re: 68 CVR rattling noise in certain frequencies
Posted: Fri Feb 19, 2016 11:16 am
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tremolo arm wrote:
I don't want to doubt what are you saying, but I've heard that by removing one power tube you're bound to unbalance the primary side load the tubes place on the transformer, and it will leave one side of the primary completely unloaded thus putting te transformers at risk.

Is that not applicable to the 68 CVR?


For purposes of a brief test, there is no risk.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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