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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Thu Nov 02, 2017 12:40 am
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Freeze spraying works on intermittent bad components, which problems are heat sensitive.

Try the "chopsticks" test, first. To find bad solder points and defective resistors.

Good hunting!


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Thu Nov 02, 2017 12:54 am
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I use sometimes this stuff, it is not useful for you amp issue.


What about lead dress, ? You never answer about that, you may not know what I mean ?


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Thu Nov 02, 2017 8:23 am
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I did try chopsticking around the board and hit every resistor other than the 4 by the filter caps.

Can you explain how to check the lead dress?

Thanks!


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Thu Nov 02, 2017 8:30 am
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mydeadblues wrote:
I did try chopsticking around the board and hit every resistor other than the 4 by the filter caps.

Can you explain how to check the lead dress?

Thanks!


Lead must be dress in special way, if not, they act like a antenna and make amp noisy.
These amps are know to have poor lead dress to save time ( $$)

How can I explain amp lead dress here ?
I don't know or it will take toooooo much time and need some sketch.

Amp must look clean as close to BMW2002 T picture

Image

Is your amp look clean ? NO
Image


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Thu Nov 02, 2017 8:58 am
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Stratle52 is correct to point out the lead dress of the amp.
The wires from pot to pot are very sensitive. They should not be hanging in the air like that. Push them all tightly against the chassis above the controls and against the metal chassis.
Also, your pics show a difference in thread height on the input jacks on the normal channel.
A common source of hum and noise is loose jack nuts at the inputs. The vibrato pics don't show the nuts, but the face looks like it has separated from the chassis at the Vibrato channel.
I know this sounds too simple, but have you tried tightening the jack nuts yet? I regularly find loose jack nuts on inputs and speakers.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Sat Nov 04, 2017 6:28 pm
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I double checked all of the nuts today and made sure that they are nice and tight. Unfortunately, they are tight and it did not fix the noise issue. I even tried pushing the face plate and the pots around a bit to double check that they are making a good connection. I did figure out that the buzzing sound is predominately coming from the 2nd channel treble pot. If I roll it back it disappears and it increases as I turn it up. I've had scratchy pots before and this does not sound like a scratchy pot. Could the pot have had something internally go wrong and perhaps I need to replace the entire pot? I also chopsticked around a little more today and moved the leads around to try to get the sound to go away, but I wasn't able to get it to disappear.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Sun Nov 05, 2017 3:08 am
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Look not the pot to me.
Ohms reading on pot out of circuit will tell if pot is good or not.

Reading on all pot's lugs and from lugs to pot body.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Sun Nov 05, 2017 4:32 am
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If you look at the photos of the circuits, you'll see that wires which must cross (esp wires carrying signal) --- are at 90-degrees with each other. Or as close to 90-degrees, as possible. This is reduce electro-magnetic coupling between the wires.

:mrgreen:


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Sun Nov 05, 2017 4:48 am
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BMW2002Ti wrote:
If you look at the photos of the circuits, you'll see that wires which must cross (esp wires carrying signal) --- are at 90-degrees with each other. Or as close to 90-degrees, as possible. This is reduce electro-magnetic coupling between the wires.

:mrgreen:


+1 ,
never parallel


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Sun Nov 05, 2017 6:49 am
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mydeadblues wrote:
upnorth2 I did find the other bias pot and started probing around with a chopstick, but I did not find any loose wires/connections.


Did you try adjusting this pot? Did it affect the hum, e.g., made it worse, less, no change?

UN


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Sun Nov 05, 2017 1:33 pm
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upnorth2 wrote:
mydeadblues wrote:
upnorth2 I did find the other bias pot and started probing around with a chopstick, but I did not find any loose wires/connections.


Did you try adjusting this pot? Did it affect the hum, e.g., made it worse, less, no change?

UN


He do ;

Oct 31 ;

" Unfortunately not. I adjusted it to the quietist position, but the problem is still present."


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Sun Nov 05, 2017 1:50 pm
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The reason I asked, he didn't make it clear that he tried adjusting the balance pot as well, just the hum pot. Maybe I missed that, gettin' old.

UN


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Sun Nov 05, 2017 1:58 pm
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upnorth2 wrote:
The reason I asked, he didn't make it clear that he tried adjusting the balance pot as well, just the hum pot. Maybe I missed that, gettin' old.

UN

Sorry I make a mistake, I though you are talking about hum pot :oops:


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Mon Nov 06, 2017 10:03 pm
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I have tried adjusting the secondary pot as well and did not get any better results. I think I might need to bring this one down to my local tech who I trust completely.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Wed Nov 08, 2017 10:15 am
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"The hum goes away when I turn up the treble."
Yes, this is normal. The treble cap doesn't pass 60Hz.
This doesn't mean the pot is bad. Its just doing its job.
Look further upstream at the V2a and Vibrato input jacks.


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