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Post subject: Pro Jr Making Spring Like Sound?
Posted: Tue Apr 07, 2015 1:00 pm
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My 1 yr old Pro Jr is now making a loud spring like sound after it warms up. Low E especially gets it going. Check that the tubes are all seated and the spring retainer is not the problem.

Any ideas? Very annoying!

Thanks!


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Post subject: Re: Pro Jr Making Spring Like Sound?
Posted: Tue Apr 07, 2015 2:02 pm
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Tube going microphonic would be my guess
tap the 12AX7 with a pencil eraser with the amp on, if the sound happens you have your culprit
Best of luck

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Post subject: Re: Pro Jr Making Spring Like Sound?
Posted: Tue Apr 07, 2015 2:18 pm
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blues bondsman wrote:
Tube going microphonic would be my guess
tap the 12AX7 with a pencil eraser with the amp on, if the sound happens you have your culprit
Best of luck


I wondered if it might be a bad tube. One music store person told me to only have a qualified tech change the tubes. That true? And thanks - I'll check it tonight.


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Post subject: Re: Pro Jr Making Spring Like Sound?
Posted: Tue Apr 07, 2015 2:46 pm
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honestly, ten minutes on youtube , here and other sites will give you everything you need to change tubes
the tube farthest to the right when looking at the back of the amp is the first stage of gain and likely the culprit
a microphonic tube in that placement causes all kinds on noise issues.

pull with a slight wobble motion and when you replace make sure the gap in the contacts match the way the original came out of the amp.

https://www.youtube.com/watch?v=JOcCMqGMs1Q

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1968 Bandmaster with 2X12 cab C-rex speakers
VHT Special 6 Ultra combo

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Post subject: Re: Pro Jr Making Spring Like Sound?
Posted: Tue Apr 07, 2015 9:27 pm
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NWLars wrote:
...a loud spring like sound...the spring retainer is not the problem...


Are you sure about that? There are two springs on the retainer, and they have been known to be the source of the sound you are describing.

Try something like these to eliminate the spring noises:

Image

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Post subject: Re: Pro Jr Making Spring Like Sound?
Posted: Tue Apr 07, 2015 9:45 pm
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shimmilou wrote:
NWLars wrote:
...a loud spring like sound...the spring retainer is not the problem...


Are you sure about that? There are two springs on the retainer, and they have been known to be the source of the sound you are describing.

Try something like these to eliminate the spring noises:

Image


That's interesting - what are those rings and where do you get them? BTW - I did the tap test as suggested and didn't find anything. However, when I was hearing the spring-sing sound I gently pushed on the first tube on the right (facing the back and without a spring retainer) and the sound stopped. This makes me think it's related to the first tube.


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Post subject: Re: Pro Jr Making Spring Like Sound?
Posted: Tue Apr 07, 2015 11:23 pm
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It does sound more like tube rattle, not microphonic. A microphonic tube would produce an uncontrolled feedback sound. If you grasped the first tube and the sound stopped, you might be correct and the first tube is rattling and should be replaced. It's easy enough to swap with a known good tube, as preamp tubes are plug and play with no worry about biasing.

The rings pictured are tube dampers, and are usually used to dampen a rattling tube (such as it seems you have), but it is better to replace the tube if possible. I use the dampers as a preventative measure in some of my combo amps, and in the case of the BJr output tubes pictured, it also damps the spring vibrations. There can be a slight loss of high end (harmonics) from the tubes when the dampers are used, and sometimes that is a good thing.

I get mine here, there are plenty of other sources.
http://www.ebay.com/sch/mr.rockinger/m.html?_nkw=&_armrs=1&_ipg=&_from=

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Post subject: Re: Pro Jr Making Spring Like Sound?
Posted: Wed Apr 08, 2015 5:05 am
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Yep Shimmilou is right on target, i forget about the el84 amps and those springs
My bad I'm a 6V6 or 6L6 guy :mrgreen:

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Post subject: Re: Pro Jr Making Spring Like Sound?
Posted: Thu May 14, 2015 10:21 pm
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I want to thank everyone for their input. I tried the tap test with a pencil as suggested and found that one of the AX7 tubes was the problem. Bought a new one, popped it in and now it's as good as ever.

Thanks and happy pickin'!


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