5150 mods... revealed w/ pictures

[droptrd]

gonna do the rest of the mods. Whats the rating on the resistors I need? 1/2 watt? 1 watt?

 

[dawnofdreamx97]

just did the mods, including the bias mod... came out really great. Uploading a clip now... sounds fucking excellent!

here is the link to the video

https://www.youtube.com/watch?v=M4D7YpedL88

 

[sled]

The jury is still out for me. I did the input Cap bypass and 10pf cap on V5B. It's lost some of the top end hair that IMO makes the 5150 or at least my 5150. I'm going to give it another month or so.

 

[Jeff Hilligan]

What are thoughts about this mod to the old 5150's compared to the 5153's? I dig the blue channel on the 3 but the rest of the amp is meh and the masters are fricken a joke unless you want to run at gig levels. I kinda remember the 5150's having the same master issues. Anyway...these tones sound really aggressive compared to the 5153. Anyone got me some comparison?

 

[Shask]

just did the mods, including the bias mod... came out really great. Uploading a clip now... sounds fucking excellent!

here is the link to the video

https://www.youtube.com/watch?v=M4D7YpedL88

Maybe it is just your settings, or style of playing, but that sounds very.... weak... to me compared to how I hear my 5150. What I like about the 5150 is it has over-the-top everything, and it sounds more pissed off than most amps out there. This video kind of sounds more reserved, more like a Marshall to me. It seems like it doesn't have that aggressive edge and massive low end boom to it, which are reasons I keep the 5150 around.... IMO...

 

[Shask]

just did the mods, including the bias mod... came out really great. Uploading a clip now... sounds fucking excellent!

here is the link to the video

https://www.youtube.com/watch?v=M4D7YpedL88

Maybe it is just your settings, or style of playing, but that sounds very.... weak... to me compared to how I hear my 5150. What I like about the 5150 is it has over-the-top everything, and it sounds more pissed off than most amps out there. This video kind of sounds more reserved, more like a Marshall to me. It seems like it doesn't have that aggressive edge and massive low end boom to it, which are reasons I keep the 5150 around.... IMO...

I understand what you are saying...but I believe Nick is not isn't a pedal with the amp. I have NEVER hear a 5150 sound like that without a pedal. Now slap a pedal in front and the amp crushes even more. I wanted a simple mod that keeps the inherent 5150 sound, but tightens up the loose and mush bottom and and get rid of "some" of the fizz. For me this does it. Some people will like it, some won't. No worries, that what make the world go round

Mine will sound like that if I use certain clear pickups, like an EMG 707, but yeah, I generally use some sort of pedal with mine Something Tubescreamer based.

I thought about trying the mods myself, but I am not sure now. I generally keep very low treble settings and use a Tubescreamer, so it stays pretty tight and fizzless on its own. Its not my favorite amp, but these aren't really my main complaints I usually get more annoyed by the over-abundance of mids.

Sort of the same reason why I prefer my Recto to my Mark III. The Mark III is an awesome amp in its own right, I just prefer the super aggressive Recto. I gotta have a destroyer amp

 

[RoidRage]

just did the mods, including the bias mod... came out really great. Uploading a clip now... sounds fucking excellent!

here is the link to the video

https://www.youtube.com/watch?v=M4D7YpedL88

Maybe it is just your settings, or style of playing, but that sounds very.... weak... to me compared to how I hear my 5150. What I like about the 5150 is it has over-the-top everything, and it sounds more pissed off than most amps out there. This video kind of sounds more reserved, more like a Marshall to me. It seems like it doesn't have that aggressive edge and massive low end boom to it, which are reasons I keep the 5150 around.... IMO...

It's because of the Negitive Feedback.... We use this in High Fi amps when we have to...

It makes things clearer, and more controlled... But, takes away dynamics and slam makes it more "Polite"... Good in moderation, but better if not needed.

Roid

 

[Shask]

just did the mods, including the bias mod... came out really great. Uploading a clip now... sounds fucking excellent!

here is the link to the video

https://www.youtube.com/watch?v=M4D7YpedL88

Maybe it is just your settings, or style of playing, but that sounds very.... weak... to me compared to how I hear my 5150. What I like about the 5150 is it has over-the-top everything, and it sounds more pissed off than most amps out there. This video kind of sounds more reserved, more like a Marshall to me. It seems like it doesn't have that aggressive edge and massive low end boom to it, which are reasons I keep the 5150 around.... IMO...

It's because of the Negitive Feedback.... We use this in High Fi amps when we have to...

It makes things clearer, and more controlled... But, takes away dynamics and slam makes it more "Polite"... Good in moderation, but better if not needed.

Roid

These mods don't effect the negative feedback, so it should be pretty big and thumpy in the poweramp on its own, just as it is stock. I generally keep the resonance on about 8 on mine, so it is pretty big and not too tight.

 

[dawnofdreamx97]

just did the mods, including the bias mod... came out really great. Uploading a clip now... sounds fucking excellent!

here is the link to the video

https://www.youtube.com/watch?v=M4D7YpedL88

Maybe it is just your settings, or style of playing, but that sounds very.... weak... to me compared to how I hear my 5150. What I like about the 5150 is it has over-the-top everything, and it sounds more pissed off than most amps out there. This video kind of sounds more reserved, more like a Marshall to me. It seems like it doesn't have that aggressive edge and massive low end boom to it, which are reasons I keep the 5150 around.... IMO...

hmm, it could be the q3 auto setting squashed it a bit, but over here the thing sounds killer. Tons of edge , presence, bite, gain, and punch. . . .

 

[RoidRage]

It's because of the Negitive Feedback.... We use this in High Fi amps when we have to...

It makes things clearer, and more controlled... But, takes away dynamics and slam makes it more "Polite"... Good in moderation, but better if not needed.

Roid

These mods don't effect the negative feedback, so it should be pretty big and thumpy in the poweramp on its own, just as it is stock. I generally keep the resonance on about 8 on mine, so it is pretty big and not too tight.

Ohhh Really?

The 10pf cap creates another negative feedback loop getting rid of some or most of the fizz. I told Mark it "Cameron-ized" the amp. It makes the amp slightly tighter as well. R9 tightens up the amp a lot depending on how low you go with a resistor. ...but too low and you choke out the amp. Too high and the amp is still flubby. Try testing a 68k, 120k and a 220k resistor. Get a feel for what it changes.

Guess I'm reading Wrong.....

Roid RAGE

 

[Shask]

It's because of the Negitive Feedback.... We use this in High Fi amps when we have to...

It makes things clearer, and more controlled... But, takes away dynamics and slam makes it more "Polite"... Good in moderation, but better if not needed.

Roid

These mods don't effect the negative feedback, so it should be pretty big and thumpy in the poweramp on its own, just as it is stock. I generally keep the resonance on about 8 on mine, so it is pretty big and not too tight.

Ohhh Really?

The 10pf cap creates another negative feedback loop getting rid of some or most of the fizz. I told Mark it "Cameron-ized" the amp. It makes the amp slightly tighter as well. R9 tightens up the amp a lot depending on how low you go with a resistor. ...but too low and you choke out the amp. Too high and the amp is still flubby. Try testing a 68k, 120k and a 220k resistor. Get a feel for what it changes.

Guess I'm reading Wrong.....

Roid RAGE

Generally in amp design the "negative feedback loop" is 99.9% the feedback loop on the power amp that makes resonance and presence controls work. His description is theoretically correct, but its not the "normal context".

That cap IMO is just creating a lowpass filter which rolls off some high-highs. I think the same effect would happen if you put a cap across the plate resistor, which is a common design choice.

 

[RoidRage]

It's because of the Negitive Feedback.... We use this in High Fi amps when we have to...

It makes things clearer, and more controlled... But, takes away dynamics and slam makes it more "Polite"... Good in moderation, but better if not needed.

Roid

These mods don't effect the negative feedback, so it should be pretty big and thumpy in the poweramp on its own, just as it is stock. I generally keep the resonance on about 8 on mine, so it is pretty big and not too tight.

Ohhh Really?

The 10pf cap creates another negative feedback loop getting rid of some or most of the fizz. I told Mark it "Cameron-ized" the amp. It makes the amp slightly tighter as well. R9 tightens up the amp a lot depending on how low you go with a resistor. ...but too low and you choke out the amp. Too high and the amp is still flubby. Try testing a 68k, 120k and a 220k resistor. Get a feel for what it changes.

Guess I'm reading Wrong.....

Roid RAGE

Generally in amp design the "negative feedback loop" is 99.9% the feedback loop on the power amp that makes resonance and presence controls work. His description is theoretically correct, but its not the "normal context".

That cap IMO is just creating a lowpass filter which rolls off some high-highs. I think the same effect would happen if you put a cap across the plate resistor, which is a common design choice.

I would agree that in effect that would get rid of the hiss, since it does reside in the top end... Can't see where the traces are going... So I would defer to Mark or either Jerry's to expand on this...

Best,

Roid Rage

 

[glpg80]

That cap IMO is just creating a lowpass filter which rolls off some high-highs. I think the same effect would happen if you put a cap across the plate resistor, which is a common design choice.

low pass filter is correct. i mentioned negative feedback loop myself and was 100% completely wrong - especially wired base to emitter (grid to cathode).

When the frequency of this filter is low, the impedance of the capacitor is high meaning most of the current will flow through the resistor network and into the grid of the tube. As the frequency increases, more current is diverted through the capacitor, less to the grid of the tube. the response is low pass.

but because tubes have miller capacitance internally, the capacitance value is altered depending on the tubes you are using and the independent miller capacitance variable that is also in the pf range. there are many other variables here as well.

across the plate resistor you are creating an RC impedance shift (reactance) of the capacitor, dependent upon the resistor value which will alter the frequency response curve of the capacitor in certain frequencies.

with the capacitor connected from plate to grid (collector to base) you are no longer creating a low pass filter but shifting the frequency response in a manner that bypasses the grid of the tube and passes un-filtered into the following gain stage (phase is important here) to be further amplified in or out of phase, giving a darker tone. since the signal is injected into the grid and not at the anode, the amplified signal will have out of phase cancellation at the impedance falling range where the capacitor begins to filter the desired frequency. current does not flow through capacitors, therefore a negative feedback term is not correct. because a resistor is not in series the reactance of the capacitor is the soul resistance and is forever changing with AC signal generation.

 

[sled]

The jury is still out for me. I did the input Cap bypass and 10pf cap on V5B. It's lost some of the top end hair that IMO makes the 5150 or at least my 5150. I'm going to give it another month or so.

As I've played it I keep coming back to... this thing sounds a lot like another amp... it's my Rev1.

Jury's still out.

 

[Motorpud]

I'm gonna do this to my buddy's 5150

 

[cliffc8488]

That cap IMO is just creating a lowpass filter which rolls off some high-highs. I think the same effect would happen if you put a cap across the plate resistor, which is a common design choice.

low pass filter is correct. i mentioned negative feedback loop myself and was 100% completely wrong - especially wired base to emitter (grid to cathode).

When the frequency of this filter is low, the impedance of the capacitor is high meaning most of the current will flow through the resistor network and into the grid of the tube. As the frequency increases, more current is diverted through the capacitor, less to the grid of the tube. the response is low pass.

but because tubes have miller capacitance internally, the capacitance value is altered depending on the tubes you are using and the independent miller capacitance variable that is also in the pf range. there are many other variables here as well.

across the plate resistor you are creating an RC impedance shift (reactance) of the capacitor, dependent upon the resistor value which will alter the frequency response curve of the capacitor in certain frequencies.

with the capacitor connected from plate to grid (collector to base) you are no longer creating a low pass filter but shifting the frequency response in a manner that bypasses the grid of the tube and passes un-filtered into the following gain stage (phase is important here) to be further amplified in or out of phase, giving a darker tone. since the signal is injected into the grid and not at the anode, the amplified signal will have out of phase cancellation at the impedance falling range where the capacitor begins to filter the desired frequency. current does not flow through capacitors, therefore a negative feedback term is not correct. because a resistor is not in series the reactance of the capacitor is the soul resistance and is forever changing with AC signal generation.

If the cap is connected from plate to grid it is "local negative feedback" and creates a lowpass filter. The plate voltage is out of phase with the grid and is fed back to the grid thereby canceling the grid at high frequencies. It's similar to putting a cap across the plate resistor except that you can use a smaller value cap and therefore reduce bias shifts as the tube goes into/out of clipping since the cap will charge/discharge quicker. So you get the same lowpass effect (smoother, less fizz) as a plate bypass cap without the farting/blocking that can occur with a large cap.

No signal 'bypasses' the grid since the plate amplitude is greater than the grid. Current flows from the plate node through the cap into the grid node. At higher frequencies the capacitor's reactance is lower so more current flows causing more cancellation. The capacitor effectively increases the tube's plate to grid internal capacitance thereby increasing the Miller capacitance.

This is not to be confused with global negative feedback which is around the power amp.

Connecting the cap from grid to cathode won't do much unless the cathode is bypassed. If not bypassed, the cathode is the same amplitude and phase as the grid so connecting a cap between them has almost no effect. If it is bypassed then, again, you create a lowpass filter by effectively increasing the grid to cathode capacitance. Typically, a cap is simply connected from grid to ground but depending upon circuit layout it may be more convenient to connect from grid to cathode. Also, connecting from grid to cathode 'delays' the influence of the cap until the cathode bypass cap's reactance is low thereby allowing more treble peaking whereas a cap from grid to ground would reduce treble peaking slightly. The Mesa MKIV lead circuit uses this approach to boost the midrange and then quickly roll off the highs.

 

[glpg80]

If the cap is connected from plate to grid it is "local negative feedback" and creates a lowpass filter.

the amount of voltage fed back determines the amount of gain reduction and the amount of distortion reduction, as well as the effective output impedance. this is the purpose of negative feedback - stability (and added tonal shaping by cutting frequencies where global NF is concerned) what is being done here is closely linked to negative feedback, but is actually more along the terms of frequency response shaping. with NF - The more voltage fed back, the less distortion, the lower the effective output impedance, the higher the dampening.

The plate voltage is out of phase with the grid and is fed back to the grid thereby canceling the grid at high frequencies. It's similar to putting a cap across the plate resistor except that you can use a smaller value cap and therefore reduce bias shifts as the tube goes into/out of clipping since the cap will charge/discharge quicker. So you get the same lowpass effect (smoother, less fizz) as a plate bypass cap without the farting/blocking that can occur with a large cap.

same thing i mentioned, only in a much simpler explanation. appreciate the clarification Cliff! the plate voltage however is not what is out of phase, the original AC signal imposed onto the tube is what alters the DC bias of the tube internally creating a mirrored output at a higher voltage. current flows from ground to hot, not the opposite way. therefore it is the AC wave that is out of phase.

No signal 'bypasses' the grid since the plate amplitude is greater than the grid. Current flows from the plate node through the cap into the grid node. At higher frequencies the capacitor's reactance is lower so more current flows causing more cancellation. The capacitor effectively increases the tube's plate to grid internal capacitance thereby increasing the Miller capacitance.

once again - DC current does not flow through a capacitor. AC current will be sent back onto the grid in an out-of-phase fashion which is where the dark term comes into play. because the DC bias is not altered or changed its a frequency response alteration. the capacitance does increase the internal grid capacitance because it is in parallel with the triode at this point - doubling the capacitance depending on the tube.

Connecting the cap from grid to cathode won't do much unless the cathode is bypassed. If not bypassed, the cathode is the same amplitude and phase as the grid so connecting a cap between them has almost no effect. If it is bypassed then, again, you create a lowpass filter by effectively increasing the grid to cathode capacitance.

why would it not decrease the capacitance since the AC voltage signal is traveling to ground (or trying) and the capacitor is effectively in series with the bypassed cathode capacitor at that point? explain this for me if you could. i do agree - bypassing it would do no good unless the cathode is bypassed because your AC signal is going to to be imposed on the cathode anyway. how negative the grid is biased by the cathode resistor by making the cathode more positive than the grid dictates how much headroom you have before grid current flows and the tube's internal plate coating wears off. hence why analog valves have to be carefully biased in comparison to SS equivalents - tubes dont like the abuse too much

Typically, a cap is simply connected from grid to ground but depending upon circuit layout it may be more convenient to connect from grid to cathode. Also, connecting from grid to cathode 'delays' the influence of the cap until the cathode bypass cap's reactance is low thereby allowing more treble peaking whereas a cap from grid to ground would reduce treble peaking slightly. The Mesa MKIV lead circuit uses this approach to boost the midrange and then quickly roll off the highs.

i never knew mesa did this. cool trick, thanks for explaining it. never thought of it like this

 

[cliffc8488]

I was going to reply in detail but you really need to study some basic electronics before you go posting stuff like this. Just about everything you wrote is incorrect.

 

[thiswaythatway]

I was going to reply in detail but you really need to study some basic electronics before you go posting stuff like this. Just about everything you wrote is incorrect.

He likes to hear himself talk, or in this case watch himself type.

 

[Mailman1971]

I was going to reply in detail but you really need to study some basic electronics before you go posting stuff like this. Just about everything you wrote is incorrect.

He likes to hear himself talk, or in this case watch himself type.

Yeah.......but how does it sound playing BACK IN BLACK?

Thats the REAL question.........