frying bacon noise in ch #1 of 1959 (with sound sample)

grainman

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(intermede) ...man I dunno if you guys try these out ....but the alnico cream celestions are quite something...
 

ampmadscientist

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yes it varies both of em without no cord plugged.... vol 1 varies the noise..not vol2

The frying bacon noise is normal, especially with carbon resistors.
There is no noisier resistor that a carbon resistor.
This will show up more in the bright channel which is also normal.

The noise actually comes from the grid resistor which is 68K or 33K.
You can use a bulk metal foil resistor which is at least 40 dB quieter than a carbon resistor.

Marshall used 2 basic methods to quiet down the noise.
A. plate to grid capacitor. The cap is 7 pf 1000 volt.
B. Hot shield.
These are the factory methods for this design.

However changing the input to capacitor coupled will work much better than a resistor.

Changing the plate resistor might help slightly, but with carbon resistors you are still underwater with mega-noise.

I have seen this many times and the best solution was capacitor coupling instead of a resistor.

2205input.png
 
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ampmadscientist

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The grid resistors must always read 34k in circuit due to the switching jacks, only way to get the correct 68k is by desoldering wires.
That is why mickeydg5 suggested that one of your switching jacks is not making a circuit, either that one of the 68k grids is open circuit - which I doubt.

It is extremely doubtful that the 68K resistor is open.
Changing it won't really solve anything unless he changes the type of resistor.

The noise of the carbon resistor is introduced at the input of the amp.
Then this noise is increased by the rest of the amplifier stages.
 
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neikeel

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It is extremely doubtful that the 68K resistor is open.
Changing it won't really solve anything unless he changes the type of resistor.
The noise of the carbon resistor is introduced at the input of the amp.
Then this noise is increased by the rest of the amplifier stages.

Frying bacon noise is not normal in this amp. Something is faulty.
Mickey's point re the switching jacks being faulty is valid because if your grid resistors are on the board, in parallel (facilitated by the switching jacks) you will only ever measure them with a meter at half that, ie 34k. If one of the switching jacks is open the grid resistor is no longer connected and will read 68k or thereabouts.
Yes, you will get some noise from a carbon film (or even worse a carbon comp) and less from metal film variants under higher signal conditions but not a frying bacon sound.
This is why I suggested getting the jacks sorted and then consider replacing the plate resistors, not because of their type but because one is probably faulty.
However the OP seems to be distracted by speaker shopping now rather than addressing the issue, so it might be time to grab the popcorn and sit back!
 

ampmadscientist

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Frying bacon noise is not normal in this amp. Something is faulty.
Mickey's point re the switching jacks being faulty is valid because if your grid resistors are on the board, in parallel (facilitated by the switching jacks) you will only ever measure them with a meter at half that, ie 34k. If one of the switching jacks is open the grid resistor is no longer connected and will read 68k or thereabouts.
Yes, you will get some noise from a carbon film (or even worse a carbon comp) and less from metal film variants under higher signal conditions but not a frying bacon sound.
This is why I suggested getting the jacks sorted and then consider replacing the plate resistors, not because of their type but because one is probably faulty.
However the OP seems to be distracted by speaker shopping now rather than addressing the issue, so it might be time to grab the popcorn and sit back!

I don't think that new resistors are going to do anything significant.

There is the possibility that what the OP hears is high frequency oscillation. I think this is more likely than the resistors...
 

grainman

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Frying bacon noise is not normal in this amp. Something is faulty.
Mickey's point re the switching jacks being faulty is valid because if your grid resistors are on the board, in parallel (facilitated by the switching jacks) you will only ever measure them with a meter at half that, ie 34k. If one of the switching jacks is open the grid resistor is no longer connected and will read 68k or thereabouts.
Yes, you will get some noise from a carbon film (or even worse a carbon comp) and less from metal film variants under higher signal conditions but not a frying bacon sound.
This is why I suggested getting the jacks sorted and then consider replacing the plate resistors, not because of their type but because one is probably faulty.
However the OP seems to be distracted by speaker shopping now rather than addressing the issue, so it might be time to grab the popcorn and sit back!
I saw a guy on the net with the exact same problem (frying bacon noise on a 1959slp) and he tried everything to stop the noise till he found a tech and when he got it back the tech just changed 4x input jacks and a faulty tube....I taught my jacks were ok cause the amp doesn't have lots of mileage but who knows maybe the jacks are [email protected]#$% or getting there...caus its started after blowing few power tubes and fuses (hum balance circuit fried too) input jacks..I might give it a try
 
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ampmadscientist

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I saw a guy on the net with the exact same problem (frying bacon noise on a 1959slp) and he tried everything to stop the noise till he found a tech and when he got it back the tech just changed 4x input jacks and a faulty tube....I taught my jacks were ok cause the amp doesn't have lots of mileage but who knows maybe the jacks are [email protected]#$% or getting there...caus its started after blowing few power tubes and fuses (hum balance circuit fried too) input jacks..I might give it a try
I saw a guy on the net with the exact same problem (frying bacon noise on a 1959slp) and he tried everything to stop the noise till he found a tech and when he got it back the tech just changed 4x input jacks and a faulty tube....I taught my jacks were ok cause the amp doesn't have lots of mileage but who knows maybe the jacks are [email protected]#$% or getting there...caus its started after blowing few power tubes and fuses (hum balance circuit fried too) input jacks..I might give it a try

1959 input.png
 

john hammond

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i think its reasonable , seeing that all/most of the postulating, extrapolating.. hypothesizing has been dispensed with regarding this repair..to now suggest, albeit tentatively, that this amp be pulled from its casing and actually examined, that things be measured...we are all ready.
thankyou.
 

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