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Lumpy
 
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Default What's this ground symbol? Resistor?

Help with this symbol and component, please.

Peavey Classic 20 guitar amp...

Schematic:
http://www.blueguitar.org/new/schem/peavey/c20schem.gif

PC Board Layout:
http://www.blueguitar.org/new/schem/peavey/c20laygr.jpg

R32, lower right corner of the schematic,
tucked under VR1, lower right corner of PC board.

Component is a fixed resistor with a value of "47FP".
What is that?

Also, the two ends of the resistor
go to ground. One ground symbol is
the traditional inverted triangle,
the other is the same triangle contained
within a circle.
What is that?

TIA - Craig


  #2   Report Post  
Phil Allison
 
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"Lumpy"

Help with this symbol and component, please.

Peavey Classic 20 guitar amp...

Schematic:
http://www.blueguitar.org/new/schem/peavey/c20schem.gif

PC Board Layout:
http://www.blueguitar.org/new/schem/peavey/c20laygr.jpg

R32, lower right corner of the schematic,
tucked under VR1, lower right corner of PC board.

Component is a fixed resistor with a value of "47FP".
What is that?



** 47 ohms " Flame Proof " type.

The resistor will not combust if overloaded , but simply go open .


Also, the two ends of the resistor
go to ground. One ground symbol is
the traditional inverted triangle,
the other is the same triangle contained
within a circle.
What is that?



** The circled one means PCB ground, the other is the usual chassis
metalwork.




........... Phil




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Lord Valve
 
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Default

Means circuit ground is 47 ohms over chassis (earth) ground.
Sometimes done to prevent loops.

LV



Lumpy wrote:

Help with this symbol and component, please.

Peavey Classic 20 guitar amp...

Schematic:
http://www.blueguitar.org/new/schem/peavey/c20schem.gif

PC Board Layout:
http://www.blueguitar.org/new/schem/peavey/c20laygr.jpg

R32, lower right corner of the schematic,
tucked under VR1, lower right corner of PC board.

Component is a fixed resistor with a value of "47FP".
What is that?

Also, the two ends of the resistor
go to ground. One ground symbol is
the traditional inverted triangle,
the other is the same triangle contained
within a circle.
What is that?

TIA - Craig




  #4   Report Post  
 
Posts: n/a
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Lord Valve wrote:
Means circuit ground is 47 ohms over chassis (earth) ground.
Sometimes done to prevent loops.

LV



Lumpy wrote:

Help with this symbol and component, please.

Peavey Classic 20 guitar amp...

Schematic:
http://www.blueguitar.org/new/schem/peavey/c20schem.gif

PC Board Layout:
http://www.blueguitar.org/new/schem/peavey/c20laygr.jpg

R32, lower right corner of the schematic,
tucked under VR1, lower right corner of PC board.

Component is a fixed resistor with a value of "47FP".
What is that?

Also, the two ends of the resistor
go to ground. One ground symbol is
the traditional inverted triangle,
the other is the same triangle contained
within a circle.
What is that?

TIA - Craig


Of course LV's right; the circled earth ground symbols are 47 ohms from
'true' chassis/earth ground; two 'slightly isolated' (by 47 ohms)
return paths (the other with no circle, straight to chassis) to reduce
ground looping (power supply noise in the signal path.)

....and 'FP' stands for 'flame proof' (to use the type of resistor that
quietly opens up when it's had enough, instead of spewing smoke and
charring the PC board like in the good old days ;-)

Also check out the 'secret capacitor' (not shown on the schematic)
between pins 1 and 2 of V1 (visible on the board layout as two meshing
'combs'); guessing ~20 pf, to stabilize the first stage preamp from
oscillation.

-Robert
QTS
http://www.Braught.com
real email addy : (remove NoSpam to reply :
Duh!)

"Aye sir, the more they overtech the plumbing, the easier it is to stop
up the drain." -- Scotty, Star Trek III

  #5   Report Post  
Lumpy
 
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Lumpy asked:
Component is a fixed resistor with a value of "47FP".
What is that?


Also, the two ends of the resistor
go to ground. One ground symbol is
the traditional inverted triangle,
the other is the same triangle contained
within a circle.
What is that?


Thanks very much Robert, Phil, LV.


craig


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