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Post subject: A couple questions for the amp guys - My Red Knob Twin
Posted: Tue Jun 26, 2012 6:04 pm
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Aspiring Musician
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I wanted to open up my red knob twin just to see how things look inside there before I put new tubes in it.It hasn't been opened since 1990 when it was built.Heres a couple photos.I'm obviously not an amp tech and I do know there are lethal voltages in there.I was extremely careful pulling it out.Does anything jump out at any of you besides the fact its a red knob twin and I know most of you guys could really care less cause of whatever reasons you have .I am just asking for some honest input.
In this first picture
a. Exactly what is encased in the white rectangular bar looking thing?
B. Exactly what may have caused this to crack?
Thanks for any help in advance[img]
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1992 Fender Newporter - Acoustic
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2011 Fender Blacktop Jazzmaster -Sunburst
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Post subject: Re: A couple questions for the amp guys - My Red Knob Twin
Posted: Tue Jun 26, 2012 9:36 pm
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That is a resistor, looks like R128. If I am looking at the correct schematic, R128 is a power supply resistor, first in line for the supply for the preamp tubes' and PI tube Plates. Resistors can crack if too much current flows through them. Any number of possibilities, including bad caps or a faulty preamp or PI tube. The smaller one in the third picture, is a resistor too, in another section of the power supply, looks like R306 for channel and reverb switching.

I would check all power supply caps, all electrolytic caps for that matter, and replace any bad resistors before/while replacing tubes.

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Post subject: Re: A couple questions for the amp guys - My Red Knob Twin
Posted: Wed Jun 27, 2012 9:01 am
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Shimmilou thank you...I kind of figured it was a resistor but why is it unlike other resistors and is encased in like it is.It almost looks like drywall mud that is dried up...really weird..Thanks you for your reply.I appreciate it
shimmilou wrote:
That is a resistor, looks like R128. If I am looking at the correct schematic, R128 is a power supply resistor, first in line for the supply for the preamp tubes' and PI tube Plates. Resistors can crack if too much current flows through them. Any number of possibilities, including bad caps or a faulty preamp or PI tube. The smaller one in the third picture, is a resistor too, in another section of the power supply, looks like R306 for channel and reverb switching.

I would check all power supply caps, all electrolytic caps for that matter, and replace any bad resistors before/while replacing tubes.

_________________
1986 Fender Sidekick Reverb 35
1990 Fender Red Knob - "The Twin"
1992 Fender Newporter - Acoustic
2000 Fender American Series Strat - Natural ash
2010 Fender Mustang 1
2011 Fender Blacktop Jazzmaster -Sunburst
2012 Fender Champion


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Profile
Post subject: Re: A couple questions for the amp guys - My Red Knob Twin
Posted: Wed Jun 27, 2012 10:25 am
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Basically, it is this way because it is a higher wattage resistor, in this case 10 watts for the big one, and 3 watts for the smaller one. The 2 watt and smaller resistors are the ones that look more like what you're used to seeing.

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Post subject: Re: A couple questions for the amp guys - My Red Knob Twin
Posted: Wed Jun 27, 2012 11:28 am
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Thanks again my friend....all my questions answered and I'm stoked you could help me out.My amp is 22 years old now and believe it or not it has not ever givin me a problem till now.( Knock on wood) I think thats a pretty good run.I know alot of the amp guys put down the red knobs for whatever reasons.I'm guessing that cause it was the first amp series that Fender starting using PCB 's and strayed from point to point...I'm not sure.I mainly use her for the clean channel.The gain channel is just ok ..... but I don't play with alot of gain anyways so its actually just right for my needs.I have treated it good and it has always ran like a top for me.This thing is louder than loud.I'm gonna change out a few resistors.. check the caps and probably replace whats needed and put new tubes in her and cross my fingers I get another 22 years out of her.Thanks bro
shimmilou wrote:
Basically, it is this way because it is a higher wattage resistor, in this case 10 watts for the big one, and 3 watts for the smaller one. The 2 watt and smaller resistors are the ones that look more like what you're used to seeing.

_________________
1986 Fender Sidekick Reverb 35
1990 Fender Red Knob - "The Twin"
1992 Fender Newporter - Acoustic
2000 Fender American Series Strat - Natural ash
2010 Fender Mustang 1
2011 Fender Blacktop Jazzmaster -Sunburst
2012 Fender Champion


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Profile
Post subject: Re: A couple questions for the amp guys - My Red Knob Twin
Posted: Wed Jun 27, 2012 11:53 am
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I love mine also but its just so heavy and loud even on 25 watt. But it sounds great.


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