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Post subject: Very Quiet Static comming from 77 Bassman
Posted: Thu Aug 14, 2014 10:36 am
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Hi Everyone, I have a very quiet static coming from my 77 Fender Bassman 50 watt. I use monster cable to connect my head to my speaker, in the 2nd Channel in the 2nd input. The static sounds like the hearing the beach a mile away. The 1st input in the 2nd channel has no static, however it is quiet from my guitar. I just replaced to the 2 6LS with a new matched pair and had it biased by a pro with a oscilloscope. He said all the caps and resistors were still in good order. Maybe a 12ax7 is going? Or Could it be grounding in my apartment? I have a newerish blues Jr, and it has the same static with the reverb off.

Again the static is extremely miniscule, you cant hear it at all when playing with a band, or even playing the guitar itself. It's only when the room is very quiet and no guitar is playing.
I hope to use this amp in a studio, so ultimately I'm worried that the static could get in the way.


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Thu Aug 14, 2014 10:50 am
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Static ; what do you call static ? Shhhh ?

1- Do you hear it with nothing connected to the amp ? This is the test to do

2- Check all 12XX7 tubes , nothing to do with output tubes

3- Check input shorting jack's contact to ground

4- Replace 12XX7 plate resistors


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Thu Aug 14, 2014 12:02 pm
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Yes it is a very quiet shhhhh, it happens when nothing is connected to the amp except the speaker


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Thu Aug 14, 2014 1:05 pm
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mikeph0210 wrote:
Yes it is a very quiet shhhhh, it happens when nothing is connected to the amp except the speaker



Ok you must check what I said


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Thu Aug 14, 2014 1:58 pm
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I would begin by looking for an aging carbon-comp resistor that's long overdue for replacement, possibly somewhere within the phase-inverter circuit. As these types of components age they become porous and absorb moisture which can cause the symptom you describe.

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: Very Quiet Static comming from 77 Bassman
Posted: Thu Aug 14, 2014 2:00 pm
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What do you mean by:
stratele52 wrote:
Static ; what do you call static ? Shhhh ?
3- Check input shorting jack's contact to ground

?


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Thu Aug 14, 2014 3:48 pm
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mikeph0210 wrote:
What do you mean by:
stratele52 wrote:
Static ; what do you call static ? Shhhh ?
3- Check input shorting jack's contact to ground

?


http://angela.com/inputjacks.aspx


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Thu Aug 14, 2014 4:57 pm
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If you have a spare 1/4-inch plug, just solder a jumper from the (+) side to the (-) side. Turn on amp and insert this shorted plug into each input jack. See if this drops the background noise. If it does, you have a dirty jack that needs some Deoxit.


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Fri Aug 15, 2014 1:15 am
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BMW2002Ti wrote:
I If it does, you have a dirty jack that needs some Deoxit.



You must use some burnishing tool to remove the "dirt" from the contact because jack's contact is not a slide one , it can't be clean just with contact cleaner.

You may use a corner of dollar paper too . Never use rough sand paper , it may destroy protective coat .

http://www.tubesandmore.com/products/S-T9338


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Fri Aug 15, 2014 7:23 am
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Do you guys really think it could be a input jack? I don't have an instrument plugged in to the input. The only input jack being used is the speaker jack.


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Fri Aug 15, 2014 8:04 am
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mikeph0210 wrote:
Do you guys really think it could be a input jack? I don't have an instrument plugged in to the input. The only input jack being used is the speaker jack.




Defective ground contact on input jack do some noise with no guitar plug in like if you plug a guitar wire in the amp with no guitar at the other end.

Can't say where is problem , could be many thing as I write few days ago ;



2- Check all 12XX7 tubes , nothing to do with output tubes

3- Check input shorting jack's contact to ground

4- Replace 12XX7 plate resistors


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Fri Aug 15, 2014 6:43 pm
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Do I check the resistors and input jacks with a meter?


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Sat Aug 16, 2014 1:43 am
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mikeph0210 wrote:
Do I check the resistors and input jacks with a meter?



Plate resistors do some noise because humidity inside because they are old . Meter can't read that . You must take chance and replace them all .
Qualified tech can say if they need to by listen the amp .

Jacks contact may read good with a meter but need to be clean ; test with guitars plug in all input in same time will tell you .
Guitars volumes to 0
Amp must now be quiet if it is jack contact issue

A defective input jack contact act like a antenna . By plug few guitars ( vol to 0 )in all jacks in same time "remove" this antenna .


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Sat Aug 16, 2014 3:30 am
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Stratele, one little trick I learned wrt noisy cc resistors. If you get a hair dryer and heat the suspected resistors --- and the noise drops --- replace those suspected resistors.

FWIW. :mrgreen:


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Post subject: Re: Very Quiet Static comming from 77 Bassman
Posted: Sat Aug 16, 2014 3:35 am
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BMW2002Ti wrote:
Stratele, one little trick I learned wrt noisy cc resistors. If you get a hair dryer and heat the suspected resistors --- and the noise drops --- replace those suspected resistors.

FWIW. :mrgreen:



I know this trick and if you leave the amp ON few hours it could do the same with its own heat .

With my experience and knowledge I don't kneed to do that , just hear the amp and do some tests


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