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Post subject: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Fri Jul 22, 2016 6:13 am
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Roadie
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I'm working on a 76' twin someone. I traced the problem to the Master volume circuit where it ties into the reverb. There is a 12K resistor tied to a .01 cap tied into a 1 meg resistor that goes to an eyelet half way up the board. There is another resistor ? that ties into the 470K coming from the reverb circuit. What is the value of that resistor. I have a 1K in there now. Does anyone know the correct value of that resistor. Thanks, Chris
[img][IMG]http://i1335.photobucket.com/albums/w669/krankster6/Twin%20MV_zpst7jcvuxh.jpg[/img][/img]


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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Fri Jul 22, 2016 7:27 am
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Can you point out where on the layout diagram you are discussing?

Thanks!

Image

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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Fri Jul 22, 2016 8:04 am
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Roadie
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Beemer
In 1976 they were switching to UL models. This is still a 100 watt, but the MV circuit is more like a 1977. Instead of the 2700 ohm resistor there is a 1 meg resistor from the .01 cap to another resistor that ties into the 470K from the reverb. Here's another pic, bit it's hard to see.

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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Fri Jul 22, 2016 8:24 am
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Roadie
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Here's a better image. It's a rats nest.

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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Sat Jul 23, 2016 3:55 pm
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If its the one going from the plate to ground, it should be 820 ohms. The schematic you need may be the aa270. That one has the master volume and all the values are visible.

Hope this helps.

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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Sat Jul 23, 2016 5:24 pm
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Roadie
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It's not the aa270, it's the 100 watt master volume on amp wares, but it's more like the 1977 UL model. It's next the the reverb circuit. There are two resistors connected to the .01 cap. The first is a 1 meg. I need the second which goes from that one to ground. I can't find it on the 135 watt schematic.


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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Sun Jul 24, 2016 2:31 am
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Krankster wrote:
It's not the aa270, it's the 100 watt master volume on amp wares, but it's more like the 1977 UL model. It's next the the reverb circuit. There are two resistors connected to the .01 cap. The first is a 1 meg. I need the second which goes from that one to ground. I can't find it on the 135 watt schematic.



135 watts schematic
http://bmamps.com/Schematics/fender/twi ... _schem.pdf

More schematic here but it is free for all... :lol:
http://bmamps.com/Tech_sch.html


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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Sun Jul 24, 2016 3:54 am
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I think this may be the applicable schematic......

http://bmamps.com/Schematics/fender/twi ... _schem.pdf

Arjay

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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Sun Jul 24, 2016 10:03 am
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Roadie
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So it looks like the 1K resistor is correct. It's connected to the 470k from the reverb. Is that your take on it? Thanks, Chris


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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Sun Jul 24, 2016 11:46 am
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If your referring to the part of the circuit labeled (a), yes. You threw me off a bit when you mentioned the master volume and the 12k resistor tied to the .01uf cap (b). But the cap tied to the 470k resistors is a .01nf.

Image

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Post subject: Re: 1976 Twin Reverb Master Volume circuit resistor values
Posted: Mon Jul 25, 2016 6:57 am
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Ok, got it. Does the "Delta-5" note = feeding signal into NORMAL channel from VIBRATO input? For a CLEAN tone?

http://bmamps.com/Schematics/fender/twi ... _schem.pdf


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