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Post subject: Noisy Twin from down under
Posted: Thu Dec 23, 2010 3:09 am
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Joined: Thu Dec 23, 2010 2:47 am
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G'day guys - and Merry Christmas,
Recently purchased a mid-2000 'Twin' (long story). It had a couple of issues that I fixed (foot pedal was working intermitently - the lamp was continually getting dim).
Last issue is the annoying hum. With nothing plugged in the reverb is 'very'noisy - sounds like a ground issue (it's actually a 'G'). The effects loop has the same issue as to be unusable.

I've taken the tank out, checked connections. rebiased it. Taken another tube and replace the stock preamo tubes one by one and still getting the noise. I took the chasis out and checked for anything obvious - sprayed all the tube sockets with contact cleaner etc. (I'm an electrician by day - a little knowledge is dangerous!)

With the tremelo engaged (with out the reverb on) I get a loud pulsing hum as well (but an octave lower than the reverb 'G' hum).

Thanks for any help guys,
Regards,
Kev


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Post subject: Re: Noisy Twin from down under
Posted: Sat Dec 25, 2010 10:41 am
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Joined: Mon Jul 16, 2007 6:51 pm
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Does it hum only when standby is on? Touch the output transformer, does it get very hot? Also look at the tubes are they red plating? Do you know if any other work has been done? You may have a bad filter cap.
However I think it will likely be a bad ground somewhere, where a ground wire got loose or a short somewhere. dont unplug the speakers if you are turning on the amp!

Does it hum when all the knobs are down to 0? Are any of the pots loose? The circuit uses the lugs on the pots to ground to the chassis. Make sure that nothing is loose and be safe while poking around in there! Very possibly a bad ground, check solder joints. Check filter cap pan if your filter caps are stil original. I had one original blow up and the fluid was everywhere.

Good luck and be safe, drain caps and unplug before poking around!

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Post subject: Re: Noisy Twin from down under
Posted: Mon Jan 03, 2011 8:13 am
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@ your PM to me :

Yes, be sure to drain caps and unplug first though!

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Being able to play and enjoy music is a gift that's often taken for granted.

Don't leave home without it!


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