The 5150 III EL34 50 watt head C137 mod, and taming the red channel

[Desertdweller]

So I did a couple of mods to the 5150 III 50w EL34 a couple years ago that really make the amp quite a bit better. I posted this on another forum then, but it's a dead now so I figure why not update it and post it here?

Blue Channel C137 Mod
I have yet to hear anyone that truly likes the stock blue channel on the 50w EL34 amp, which is an absolute shame because all the other 5150 III heads have an amazing blue channel. Fender put in a fail-safe to fix this thankfully, and I'm not the first to do this simple and great mod. Simply snipping a small capacitor fixes this.

This is the easiest mod one can make to this amp. However, if you're not tech savvy at least a bit, hire a tech to do this. Innards of amplifiers have enough current to kill, so DO THIS AT YOUR OWN RISK as always. What I did is just snip out capacitor 137 and the blue channel comes to life, making it just as great as the blue channel on the other 5150 III amps.

Now that I've modded that blue channel, I screwed the amp back into the chassis and kept the front off so I could mess with tubes to modify the sound of the red channel.

Red Channel Gain kick-down through tube selection
This will be way easier, as it's just tube preference, they're preamp tubes so there's no worry about biasing, these tube changes will:

1) Make the gain knob more of a usable sweep so it doesn't hit full saturation at 10 o'clock, and
2) Get rid of the squeaky midrange the red channel can sometimes have.

I wound up with this configuration that accomplished both:

V1: First driver for all 3 channels. I used Mesa SPAX7-A (a decently high-end 12AX7) originally and now have a Tung Sol 12ax7 in there. I usually use Tung Sols in V1 of all my amps, just my preference, I can hear a difference even if Glenn Fricker can't. Lower noise floor and it just punches harder IMO.

Red channel specific tubes, V2-4 are all the additional gain stages for the red channel:
V2: JJ 12au7, much lower gain tube, makes the gain knob sweep come to life. 40 is the new 30, right? Well 2 or 3 o'clock is the new 10 o'clock on the dial.
V3: Sovtek 12ax7LPS, to sweeten the midrange and make the channel sound more balanced
V4: Mesa 12ax7A, just a good tube! A Tung Sol would do nicely here too.

Conclusion: made an already awesome amp a lot better with a few small tweaks. Slightly lower noise all around, tighter/thrashier blue channel, and a singing lead red channel that now has some variation.

 

[KingsXJJ]

Excellent detective work. I’d like to see similar observations on the 6L6 50 watt head and 100 watt head if anyone has been so bold!

 

[sleewell]

Hell yea. Nice!


My 5153 was Kruse modded before I got it. Amp is killer stock but w some mods its downright nasty.

 

[Desertdweller]

Excellent detective work. I’d like to see similar observations on the 6L6 50 watt head and 100 watt head if anyone has been so bold!

Great idea! For the 6L6 variants, the blue channel mod wouldn't be necessary as those amps come stock with the right-sounding blue channel to begin with. They would both probably benefit from the red channel being de-gained a bit though, and that 12au7 in V2 would be a great place to start. Even with it in there, the channel has plenty of gain.

 

[Orvillain]

Stock blue channel is amazing, and I've seen loads of people saying that. It actually surprises me you haven't tbh! It's pretty famous for being a great sound, to the point where loads of us wish the amp had 1 green channel and 2 blue channels! The red channel on that amp is faaaaaar too gainy and brittle sounding IMHO.

 

[Desertdweller]

Stock blue channel is amazing, and I've seen loads of people saying that. It actually surprises me you haven't tbh! It's pretty famous for being a great sound, to the point where loads of us wish the amp had 1 green channel and 2 blue channels! The red channel on that amp is faaaaaar too gainy and brittle sounding IMHO.

My experience is quite different with the blue channel. It sounds great on every EVH head except the 50w EL34 amp, which is tubby and undefined. That's why the C137 mod is growing in popularity. Just snipping one cap and it's the bold and beautiful EVH blue channel we all love.

Agreed somewhat on the red channel. I don't find it brittle at all, but it is too gainy, which is why I stepped the gain down a touch to make better use of the full range of the gain knob.

 

[Deadpan]

It was said that Eddie wanted more low mids on the blue so they add C137. Turned it into a doom machine but that's not my thing. Clipping one leg and it is fantastic.

Note this is 50 watt el34 only.

 

[Hightech8988]

So I did a couple of mods to the 5150 III 50w EL34 a couple years ago that really make the amp quite a bit better. I posted this on another forum then, but it's a dead now so I figure why not update it and post it here?

Blue Channel C137 Mod
I have yet to hear anyone that truly likes the stock blue channel on the 50w EL34 amp, which is an absolute shame because all the other 5150 III heads have an amazing blue channel. Fender put in a fail-safe to fix this thankfully, and I'm not the first to do this simple and great mod. Simply snipping a small capacitor fixes this.

This is the easiest mod one can make to this amp. However, if you're not tech savvy at least a bit, hire a tech to do this. Innards of amplifiers have enough current to kill, so DO THIS AT YOUR OWN RISK as always. What I did is just snip out capacitor 137 and the blue channel comes to life, making it just as great as the blue channel on the other 5150 III amps.

View attachment 4161

Now that I've modded that blue channel, I screwed the amp back into the chassis and kept the front off so I could mess with tubes to modify the sound of the red channel.

View attachment 4162

Red Channel Gain kick-down through tube selection
This will be way easier, as it's just tube preference, they're preamp tubes so there's no worry about biasing, these tube changes will:

1) Make the gain knob more of a usable sweep so it doesn't hit full saturation at 10 o'clock, and
2) Get rid of the squeaky midrange the red channel can sometimes have.

I wound up with this configuration that accomplished both:

V1: First driver for all 3 channels. I used Mesa SPAX7-A (a decently high-end 12AX7) originally and now have a Tung Sol 12ax7 in there. I usually use Tung Sols in V1 of all my amps, just my preference, I can hear a difference even if Glenn Fricker can't. Lower noise floor and it just punches harder IMO.

Red channel specific tubes, V2-4 are all the additional gain stages for the red channel:
V2: JJ 12au7, much lower gain tube, makes the gain knob sweep come to life. 40 is the new 30, right? Well 2 or 3 o'clock is the new 10 o'clock on the dial.
V3: Sovtek 12ax7LPS, to sweeten the midrange and make the channel sound more balanced
V4: Mesa 12ax7A, just a good tube! A Tung Sol would do nicely here too.

Conclusion: made an already awesome amp a lot better with a few small tweaks. Slightly lower noise all around, tighter/thrashier blue channel, and a singing lead red channel that now has some variation.

Does anyone know how this Mod works with the blue channel where people add a Switch to it so u can go back and forth between the vocings rather then cut the leg of C137?
I seen peoples amps and a video where people add a switch and like i said you can go back and forth i just dont know how to do it.
If someone does and shows what it looks like on the Board i would take a chance at trying it.

 

[RaceU4her]

just got this amp and havent even played it yet, actually planned to jam on it tomorrow as its supposed to pour all day. i might just do this right off the bat. am i gonna be safe if i wear some rubber gloves or some shit while cutting the thing?

 

[mavrick102000]

Seriously, If you don't have a mentor, and you don't know what your doing , stay out of the inside of the amp. If you make a mistake, even if it doesn't kill you it can end your playing days very quickly.

I've seen some injuries from guys modifying tube amps for amateur radio, and it can be brutal - i.e. missing chunks of finger or a portion of their hand.

1000-3000 volts can do some serious tissue damage at a minimum.

 

[RaceU4her]

Aren’t there ways to discharge the amp so it’s safe?? A tech had me pull the power chord once with the amp on to poke around with a chop stick?

 

[Deadpan]

If the amp has been shipped and not plugged in for days there should be no charge in the caps. The main thing is you don't want to touch the caps. Pulling the chassis and putting it back can be tricky. Be sure tonfinger tighten the bolts when reassembling to avoid cross thread.

Clipping one leg on c137 isn't hard but it's small and I couldn't imagine doing it with gloves on.

You are always at your own risk but there really isn't much to it.

 

[Bob Zaod]

So I did a couple of mods to the 5150 III 50w EL34 a couple years ago that really make the amp quite a bit better. I posted this on another forum then, but it's a dead now so I figure why not update it and post it here?

Blue Channel C137 Mod
I have yet to hear anyone that truly likes the stock blue channel on the 50w EL34 amp, which is an absolute shame because all the other 5150 III heads have an amazing blue channel. Fender put in a fail-safe to fix this thankfully, and I'm not the first to do this simple and great mod. Simply snipping a small capacitor fixes this.

This is the easiest mod one can make to this amp. However, if you're not tech savvy at least a bit, hire a tech to do this. Innards of amplifiers have enough current to kill, so DO THIS AT YOUR OWN RISK as always. What I did is just snip out capacitor 137 and the blue channel comes to life, making it just as great as the blue channel on the other 5150 III amps.

View attachment 4161

Now that I've modded that blue channel, I screwed the amp back into the chassis and kept the front off so I could mess with tubes to modify the sound of the red channel.

View attachment 4162

Red Channel Gain kick-down through tube selection
This will be way easier, as it's just tube preference, they're preamp tubes so there's no worry about biasing, these tube changes will:

1) Make the gain knob more of a usable sweep so it doesn't hit full saturation at 10 o'clock, and
2) Get rid of the squeaky midrange the red channel can sometimes have.

I wound up with this configuration that accomplished both:

V1: First driver for all 3 channels. I used Mesa SPAX7-A (a decently high-end 12AX7) originally and now have a Tung Sol 12ax7 in there. I usually use Tung Sols in V1 of all my amps, just my preference, I can hear a difference even if Glenn Fricker can't. Lower noise floor and it just punches harder IMO.

Red channel specific tubes, V2-4 are all the additional gain stages for the red channel:
V2: JJ 12au7, much lower gain tube, makes the gain knob sweep come to life. 40 is the new 30, right? Well 2 or 3 o'clock is the new 10 o'clock on the dial.
V3: Sovtek 12ax7LPS, to sweeten the midrange and make the channel sound more balanced
V4: Mesa 12ax7A, just a good tube! A Tung Sol would do nicely here too.

Conclusion: made an already awesome amp a lot better with a few small tweaks. Slightly lower noise all around, tighter/thrashier blue channel, and a singing lead red channel that now has some variation.

How did the build itself look inside? I recently watched a video of a Tech that claimed it was shoddy on those, complete with video. It was one reason I recently passed on an EL34 50w head for 600 smackers locally.

 

[Blix]

just got this amp and havent even played it yet, actually planned to jam on it tomorrow as its supposed to pour all day. i might just do this right off the bat. am i gonna be safe if i wear some rubber gloves or some shit while cutting the thing?

Just don't do it barefoot on a wet floor while holding on to a copper conduit with the other and and you'll be fine. Snipping a cap is easy. :)

 

[Bob Zaod]

Does anyone know how this Mod works with the blue channel where people add a Switch to it so u can go back and forth between the vocings rather then cut the leg of C137?
I seen peoples amps and a video where people add a switch and like i said you can go back and forth i just dont know how to do it.
If someone does and shows what it looks like on the Board i would take a chance at trying it.

Yes that would absolutely work. It's just a capacitor it can be taken in and out of the circuit with a switch.

 

[Bob Zaod]

So I did a couple of mods to the 5150 III 50w EL34 a couple years ago that really make the amp quite a bit better. I posted this on another forum then, but it's a dead now so I figure why not update it and post it here?

Blue Channel C137 Mod
I have yet to hear anyone that truly likes the stock blue channel on the 50w EL34 amp, which is an absolute shame because all the other 5150 III heads have an amazing blue channel. Fender put in a fail-safe to fix this thankfully, and I'm not the first to do this simple and great mod. Simply snipping a small capacitor fixes this.

This is the easiest mod one can make to this amp. However, if you're not tech savvy at least a bit, hire a tech to do this. Innards of amplifiers have enough current to kill, so DO THIS AT YOUR OWN RISK as always. What I did is just snip out capacitor 137 and the blue channel comes to life, making it just as great as the blue channel on the other 5150 III amps.

View attachment 4161

Now that I've modded that blue channel, I screwed the amp back into the chassis and kept the front off so I could mess with tubes to modify the sound of the red channel.

View attachment 4162

Red Channel Gain kick-down through tube selection
This will be way easier, as it's just tube preference, they're preamp tubes so there's no worry about biasing, these tube changes will:

1) Make the gain knob more of a usable sweep so it doesn't hit full saturation at 10 o'clock, and
2) Get rid of the squeaky midrange the red channel can sometimes have.

I wound up with this configuration that accomplished both:

V1: First driver for all 3 channels. I used Mesa SPAX7-A (a decently high-end 12AX7) originally and now have a Tung Sol 12ax7 in there. I usually use Tung Sols in V1 of all my amps, just my preference, I can hear a difference even if Glenn Fricker can't. Lower noise floor and it just punches harder IMO.

Red channel specific tubes, V2-4 are all the additional gain stages for the red channel:
V2: JJ 12au7, much lower gain tube, makes the gain knob sweep come to life. 40 is the new 30, right? Well 2 or 3 o'clock is the new 10 o'clock on the dial.
V3: Sovtek 12ax7LPS, to sweeten the midrange and make the channel sound more balanced
V4: Mesa 12ax7A, just a good tube! A Tung Sol would do nicely here too.

Conclusion: made an already awesome amp a lot better with a few small tweaks. Slightly lower noise all around, tighter/thrashier blue channel, and a singing lead red channel that now has some variation.

I opened mine up to check BIAS and it was ice cold (34mV). Set it to 58mV and saw C137 on my way out so I carefully snipped it so I could just put some solder there to put it back if I want. Cant test at volume right now wife is sleeping but with the volume low I don't notice anything different. I am sure I will when I can turn it up tomorrow...err umm today I guess at this point.

 

[Desertdweller]

I opened mine up to check BIAS and it was ice cold (34mV). Set it to 58mV and saw C137 on my way out so I carefully snipped it so I could just put some solder there to put it back if I want. Cant test at volume right now wife is sleeping but with the volume low I don't notice anything different. I am sure I will when I can turn it up tomorrow...err umm today I guess at this point.

The Blue channel should be dramatically tighter with the C137 snip. It does not affect any other channels.

 

[frankerector]

So I did a couple of mods to the 5150 III 50w EL34 a couple years ago that really make the amp quite a bit better. I posted this on another forum then, but it's a dead now so I figure why not update it and post it here?

Blue Channel C137 Mod
I have yet to hear anyone that truly likes the stock blue channel on the 50w EL34 amp, which is an absolute shame because all the other 5150 III heads have an amazing blue channel. Fender put in a fail-safe to fix this thankfully, and I'm not the first to do this simple and great mod. Simply snipping a small capacitor fixes this.

This is the easiest mod one can make to this amp. However, if you're not tech savvy at least a bit, hire a tech to do this. Innards of amplifiers have enough current to kill, so DO THIS AT YOUR OWN RISK as always. What I did is just snip out capacitor 137 and the blue channel comes to life, making it just as great as the blue channel on the other 5150 III amps.

View attachment 4161

Now that I've modded that blue channel, I screwed the amp back into the chassis and kept the front off so I could mess with tubes to modify the sound of the red channel.

View attachment 4162

Red Channel Gain kick-down through tube selection
This will be way easier, as it's just tube preference, they're preamp tubes so there's no worry about biasing, these tube changes will:

1) Make the gain knob more of a usable sweep so it doesn't hit full saturation at 10 o'clock, and
2) Get rid of the squeaky midrange the red channel can sometimes have.

I wound up with this configuration that accomplished both:

V1: First driver for all 3 channels. I used Mesa SPAX7-A (a decently high-end 12AX7) originally and now have a Tung Sol 12ax7 in there. I usually use Tung Sols in V1 of all my amps, just my preference, I can hear a difference even if Glenn Fricker can't. Lower noise floor and it just punches harder IMO.

Red channel specific tubes, V2-4 are all the additional gain stages for the red channel:
V2: JJ 12au7, much lower gain tube, makes the gain knob sweep come to life. 40 is the new 30, right? Well 2 or 3 o'clock is the new 10 o'clock on the dial.
V3: Sovtek 12ax7LPS, to sweeten the midrange and make the channel sound more balanced
V4: Mesa 12ax7A, just a good tube! A Tung Sol would do nicely here too.

Conclusion: made an already awesome amp a lot better with a few small tweaks. Slightly lower noise all around, tighter/thrashier blue channel, and a singing lead red channel that now has some variation.

My brother bought me a 5150iii 212 combo amp with el34s.

I am new to this type of beast.
I love the sound so far and looked at the tweaks and mods.

Is there anything I could do to it right out of the box
Like snip that resistor at 137?

I’m very handy with a multimeter and i believe I’d easily preform these mods.

Any help or input is fully appreciated.

Frank

 

[deadpool_25]

My brother bought me a 5150iii 212 combo amp with el34s.

I am new to this type of beast.
I love the sound so far and looked at the tweaks and mods.

Is there anything I could do to it right out of the box
Like snip that resistor at 137?

I’m very handy with a multimeter and i believe I’d easily preform these mods.

Any help or input is fully appreciated.

Frank

Play it for a bit and see how you like it. Some people do like the amp as is. The C137 resistor was mistakenly added to the circuit and Eddie said he liked it that way so they were all but forced to leave it that way even though Howard Kaplan (the designer) didn’t want to.

Eddie wasn’t the only one who liked it that way either; I’ve seen people in person and on forums who like it as-is. It makes the blue channel kinda loose and wooly. Personally, I didn’t hate it but it was me least favorite channel throughout the entire 5150 range.

I had all three 50w heads at the same time. I decided to sell one off and the EL34 was the one I decided to let go of. I never did the C137 mod myself but I looked into it, going as far as to pull the amp chassis and locate that capacitor. I could see it would be a super easy mod and would’ve done it if I was going to keep the amp.

So again, I’d say play it a bit and see what you think. You might like it as-is. If you find the blue channel a bit too dark and wooly, then go ahead and clip one leg of that capacitor. It’s a fairly short leg but if you clip it kinda in the middle, you’ll have the ability to solder it back in if you ever want.

Edit: as for other popular “mods”, if you find the amp has too much gain (a common opinion especially on the red channel), you can put a lower gain preamp tube in there. I experimented with a 12AU7 in my 5153 heads. It definitely lowered the gain significantly. That was pretty good but I eventually settled on a 5751. IIRC I put that in V1 lowering the gain on all the channels a little less than the 12AU7.

 

[frankerector]

Play it for a bit and see how you like it. Some people do like the amp as is. The C137 resistor was mistakenly added to the circuit and Eddie said he liked it that way so they were all but forced to leave it that way even though Howard Kaplan (the designer) didn’t want to.

Eddie wasn’t the only one who liked it that way either; I’ve seen people in person and on forums who like it as-is. It makes the blue channel kinda loose and wooly. Personally, I didn’t hate it but it was me least favorite channel throughout the entire 5150 range.

I had all three 50w heads at the same time. I decided to sell one off and the EL34 was the one I decided to let go of. I never did the C137 mod myself but I looked into it, going as far as to pull the amp chassis and locate that capacitor. I could see it would be a super easy mod and would’ve done it if I was going to keep the amp.

So again, I’d say play it a bit and see what you think. You might like it as-is. If you find the blue channel a bit too dark and wooly, then go ahead and clip one leg of that capacitor. It’s a fairly short leg but if you clip it kinda in the middle, you’ll have the ability to solder it back in if you ever want.

Edit: as for other popular “mods”, if you find the amp has too much gain (a common opinion especially on the red channel), you can put a lower gain preamp tube in there. I experimented with a 12AU7 in my 5153 heads. It definitely lowered the gain significantly. That was pretty good but I eventually settled on a 5751. IIRC I put that in V1 lowering the gain on all the channels a little less than the 12AU7.

I’ll leave my address for all those tubes.
So far I love the amp.
I love the sound and feel of the Red, the sound and feel of the Blue, I love the Hardness of the crunch.
And what’s not to love about the green.
I guess if I decided to get a modeler it would go green.
I don’t know.
Really I don’t have a clue as to what I would do.
But the Heavy side of Blue and the Red are to die for.
All around perfection.