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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Mon Oct 23, 2017 1:19 am
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BMW2002Ti wrote:
Needs replacing, for sure. Most likely, majority of your hum issue.

Prolly, one tube's heater line shorted --- either internally or the wiring to the socket -- at one time.

NB: Check the fuse in your unit. I believe it's a 3 or 4-amp Slow Blow. Check the schematic.

:)

Good luck!

l


+1

Always check fuse on second hand amp, sometimes it is the wrong one and you 'll damage your amp


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Mon Oct 23, 2017 1:28 am
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mydeadblues wrote:
Here are a few pictures with the chassis out:

Image

!


This amp see some service, ( on 6L6 ) all four 470 ohms are new, one socket have two 1K in parallel.
All 6l6 have 1 ohms to ground to check bias ; good thing.

6L6's
Heater, look carefully and clean wire dress . Look at BMW2002Ti chassis picture.
Check solder.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Mon Oct 23, 2017 3:44 pm
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For now you should be able to disconnect that pot completely and add an artificial CT with two 100 ohm resistors. Put one resistor from each wire (black and white) that were attached to the pot, twist the other ends of the resistors together and run them to ground.

UN


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Fri Oct 27, 2017 11:39 am
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I just placed an order for a replacement hum balance pot. I'm crossing my fingers that this solves the problem. I'll let you guys know how it goes after I install it.

Thanks!


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Fri Oct 27, 2017 11:42 am
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You don't have two 100 ohms resistors in stock ?


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Fri Oct 27, 2017 12:37 pm
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I'll take a look and see what I have lying around. Maybe I'll try alligator clipping them in to test it until the pot comes in.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Fri Oct 27, 2017 12:47 pm
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mydeadblues wrote:
I'll take a look and see what I have lying around. Maybe I'll try alligator clipping them in to test it until the pot comes in.


100 to 200 ohms will work, both should be the same.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Tue Oct 31, 2017 5:55 pm
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Well I installed the new hum balance pot today and the problem is still there. I guess it's back to the drawing board.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Tue Oct 31, 2017 6:13 pm
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Adjusting the hum pot or balance pot doesn't change the hum issue?


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Tue Oct 31, 2017 6:24 pm
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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: Tue Oct 31, 2017 10:57 pm
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Try moving the 6L6GC tubes around. Say, V8 moved to V9 and vice versa. Then, try adjusting the balance pot.

http://ampwares.com/schematics/twin_reverb_aa270.pdf

Trying to see if you have mismatching issues with the output tubes, which the balance pot is having hard time adjusting out.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Wed Nov 01, 2017 1:50 am
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Hum on one channel only as you write before or both ?

One channel, it is not 6L6s issue.
Look a bad lead dress or you make mistake in testing something.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Wed Nov 01, 2017 3:17 pm
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Initially it sounded like a humming noise that was affected by both channels. After replacing the hum balance pot the noise sounds more like static/buzzing. It is primarily on the 2nd channel, but it does increase slightly from channel 1 as well. I read somewhere that the 100k resistors in the preamp section are often culprits for static on these old twins. Should I start replacing resistors or does anyone have any other suggestions that might be causing the problem?

Thanks!


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Wed Nov 01, 2017 3:29 pm
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Not easy to answer without listening the amp.
Old 100 K resistor make more a hiss.

Could be a bad lead dress.


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Post subject: Re: Help 1970's Fender Twin Reverb Silverface Hum/Noise Prob
Posted: Wed Nov 01, 2017 4:02 pm
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I'll try to shoot a video of the noise to help clarify the problem. I was thinking about spraying some freeze spray on various resistors. I've never really used it, but I have read it could be good for isolating symptomatic caps/resistors. Has anyone ever used freeze spray and if so, would you advise trying it on this particular problem?

Thanks,


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