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Post subject: Blues Jr Volume Fade
Posted: Fri Apr 27, 2012 7:05 pm
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Hey guys,
apologies for my description, i don't really know much about amps, their circuitry and what not so may not be using the correct terminology, but will endeavour to describe them the best i can.
So today i was just jamming to some backing tracks with my standard version 2 blues jr. volume was moderate bedroom levels (volume 6, master 4) and an overdrive pedal between guitar and amp.
Here's my problem, after playing for a while the volume would fade a bit, not completely, but a noticable amount. After maybe 5 to 10 seconds of this lowered volume, the full volume would surge back. and then id play some more for maybe a few minutes and it would fade out again, only to surge back after a bit.
Is this just a sign of needing new tubes? i havent replaced the stock ones since i bought it a year or so ago and its only been for bedroom use so not loud, but used everyday. It was a store floor model so may have been used a bit already when i got it. Also, the tubes are all still glowing.

I know its difficult to diagnose problems over the internet via the description, but it would help for me to describe the next step. Ill most likely just end up taking it to a tech, but it would be nice to have some idea about what im dealing with in the mean time.

Thanks alot, Ray.


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Post subject: Re: Blues Jr Volume Fade
Posted: Fri Apr 27, 2012 7:22 pm
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It could be a tube, but sounds to me as if it is poor solder joint(s), possibly on one of the screen grid resistors and/or tube socket connections.

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Post subject: Re: Blues Jr Volume Fade
Posted: Fri Apr 27, 2012 8:16 pm
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Are you leaning on the volume knob? :wink:

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Post subject: Re: Blues Jr Volume Fade
Posted: Sun Apr 29, 2012 8:21 pm
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Cheers Shimmi.
Ahhh Adey, if only i were, it would mean there was an easy remedy :)

Does anyone else have any input? I initially thought it was tubes, because i figured the fade in and out of volume seemed like something tubes would do, and that if it were wiring slash electrical etc, the changes in volume would be more abrupt and instant and the sound would cut altogether?


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Post subject: Re: Blues Jr Volume Fade
Posted: Mon Apr 30, 2012 4:21 am
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A WAG might be the output tubes are biased too hot. And their gain drops as they overheat. Then, comes back as you allow them to cool a bit. Try a small floor fan pointed UP, behind the amp, to allow heat to rise out of the cab. And see if this helps. If this happens, may want a tech to checked their idle bias.

Second guess would be worse situation. Parasitic oscillation. An instability that sets in motion supersonic output that robs sonic power from your amp. Overheats it & can eventually lead to failure. Tech needed.


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