The Mother of All 6505+ 112 Mods!!!
Posted: Sat Mar 26, 2016 11:54 pm
I have spent the past few days with the chassis pulled on my 6505+ 112 combo (which will become a head in due time), modifying it quite heavily in fact. I, like many of you, love the amp for its heavy tones, but feel that in its stock form, it's quite underwhelming on the rhythm channel if you try to coax any clean tones from it; be it EQ changes, guitar changes, or even tube changes. That said, I have spent the past few months researching various mods and memorizing schematics from the entire 6505 line in the hopes of transforming this amp to the next level, and today I feel like I have accomplished this.
In advance, I'd like to thank any and all fellow Peavey forum members who have posted any mods and suggested advice, as it has helped me greatly in several of the changes I have made to my amplifier. I apologize if I may not remember your names first off. For further reference, I would like to thank Matt at Atomium Amplification for sharing some of his 5150II/6505+ head mods on his Tumblr page. After much research and comparison between the 6505+ head and 112 combo's schematics, I have found that the preamp section of both amps are very similar if not nearly identical with each other, the difference being the power section and FX loop. So most of the preamp mods were done from this blog post by plugging in the proper component from the schematic (Example: R93 on the 6505+ head is equivalent to R51 on the 112 combo).
DISCLAIMER: I am not taking credit for any of these mods. I have not developed any of them myself; I am simply sharing the specific modifications done to my own amplifier. Perform these mods at your own risk. I am not liable for any damage caused to your person or your equipment.
Now let's talk caps and resistors, shall we?
So the first two things I did were months ago, and were picked up from here on the Peavey forum, and that was to cut some of the low-volume fizz from the lead channel and some of the extra fizz encountered from using the FX loop.
As many of us know, using the FX loop on this amp drastically alters the tone and generally not in a good way. I soldered a .022µF capacitor in parallel with R86, and this made the loop about 90% more transparent.
I then removed the capacitor C30 from the lead channel, which is a treble-bleed cap on the gain pot. Doing this made the amp sound more organic at lower levels.
Last night, I went about altering the rhythm channel to clean up a bit more, and it led to modifying most aspects of the whole preamp.
I first replaced the treble-bleed cap at C36 (which is a 6.8nf cap) with a 100pF cap. This made the channel less boxy at lower volumes and more organic in the sweep of the gain pot. I then replaced the 470KΩ resistor at R91 with a 1MΩ resistor, the 6.8KΩ resistor at R69 with a 10KΩ, and the 68nF at C25 with a .047µF to counteract the drop in volume from the previous mod. I removed the resistor at R13 to create more bass punch in the cleans, similar to a Fender amp. Replacing the .022µF cap at C34 with a .001µF gave a subtly tighter rhythm crunch, more similar to a Marshall. And to finish it off, I removed the 100pF cap at C47 to bring the rhythm tone stack closer to standard Marshall values.
I was already happy with the lead channel, but I went ahead and did some mods to it too “while I was still under the hood.” Most of these are either specs from the original 5150 or Soldano SLO100. I started off by replacing the 470pF cap at C5 with a 470KΩ resistor and a .0022µF cap in parallel, which is the spec for the original 5150. This gives a rounder, fatter bottom. I then replaced the .001µF cap at C26 with a .022µF, for much of the same reason. Replacing the 37.4KΩ resistor at C12 with a 39KΩ also brought me to SLO/5150 spec. Last, I swapped the 33KΩ resistor at R25 with a 47KΩ resistor and two 330pF capacitors in parallel (which is the exact same as a 47KΩ resistor and a 660pF cap in parallel, if you're curious). This thickened up the mids a bit, resulting in a less-scooped sound, while also cutting some of the fizz out.
Today I took it a step further, and went about replacing the 6.8nF caps at C37 and C74 with .01µF caps, thus lowering the range of the resonance controls by roughly an octave, which opened up the EQ a bit in both channels. I then replaced the 2.2KΩ resistors at R52 and R53 with 2KΩ resistors, yielding a slightly hotter bias in V1B and V2A, which affect the rhythm channel. This sweetened things up a hair. I also replaced the 220KΩ resistor at R14 with a 200KΩ to cause the power tubes to run a little hotter.
THE VERDICT: It's a game changer. I actually have a working clean sound, and it's much more sensitive to changes between guitars, pickups, coil splits, etc. It's not quite sparkling Fender clean, but is very serviceable, and with chorus, reverb, et cetera, it can be very nice (bear in mind I've only demo'd it dry at this point). The crunch sound is very Marshall-esque, and lends itself very well to classic rock and blues (neck or middle position with a Tele is where it's at!!!) and some of the semi-driven stuff I do in my own music (which is alternative rock/metal). The lead channel sounds rounder, with thicker mids and not as brittle or fizzy, and thus not so metal; however, still has more than enough gain on tap for metal, and I'd bet it'd still LOVE EMGs.
Overall, it took me a total of four hours of work spread out over two days. In my opinion, with the right tools and about $25 in components, it's definitely worth it. It still has the 5150/6505 sound, but it's much more versatile like this. It feels more like a tube amp, without all the extra fizz from the preamp and a slightly hotter bias on the tubes.
For tubes, I'm using a JJ 5751 in V1, Sovtek 12AX7LPS in V2, JJ ECC83S (12AX7) in V3 and V4, and a JJ ECC832 (12DW7) in V5. I haven't changed power tubes yet (still on the stock Ruby 6L6GCs), that will be next week when I grab some JJ 6L6s for that.\
As I did not develop these mods, these values on caps and resistors are not set in stone. A lot of them are within a suggested range by those who did develop them. For more information you can go here: http://atomiumamps.tumblr.com/post/9393 ... -6505-mods. He's a lot more detailed about this. While you're at it, Google schematics for both the 5150II head and 6505+ 112 combo, these would also be useful. Again, thank you for your help and info and I hope to hear from you soon!!
In advance, I'd like to thank any and all fellow Peavey forum members who have posted any mods and suggested advice, as it has helped me greatly in several of the changes I have made to my amplifier. I apologize if I may not remember your names first off. For further reference, I would like to thank Matt at Atomium Amplification for sharing some of his 5150II/6505+ head mods on his Tumblr page. After much research and comparison between the 6505+ head and 112 combo's schematics, I have found that the preamp section of both amps are very similar if not nearly identical with each other, the difference being the power section and FX loop. So most of the preamp mods were done from this blog post by plugging in the proper component from the schematic (Example: R93 on the 6505+ head is equivalent to R51 on the 112 combo).
DISCLAIMER: I am not taking credit for any of these mods. I have not developed any of them myself; I am simply sharing the specific modifications done to my own amplifier. Perform these mods at your own risk. I am not liable for any damage caused to your person or your equipment.
Now let's talk caps and resistors, shall we?
So the first two things I did were months ago, and were picked up from here on the Peavey forum, and that was to cut some of the low-volume fizz from the lead channel and some of the extra fizz encountered from using the FX loop.
As many of us know, using the FX loop on this amp drastically alters the tone and generally not in a good way. I soldered a .022µF capacitor in parallel with R86, and this made the loop about 90% more transparent.
I then removed the capacitor C30 from the lead channel, which is a treble-bleed cap on the gain pot. Doing this made the amp sound more organic at lower levels.
Last night, I went about altering the rhythm channel to clean up a bit more, and it led to modifying most aspects of the whole preamp.
I first replaced the treble-bleed cap at C36 (which is a 6.8nf cap) with a 100pF cap. This made the channel less boxy at lower volumes and more organic in the sweep of the gain pot. I then replaced the 470KΩ resistor at R91 with a 1MΩ resistor, the 6.8KΩ resistor at R69 with a 10KΩ, and the 68nF at C25 with a .047µF to counteract the drop in volume from the previous mod. I removed the resistor at R13 to create more bass punch in the cleans, similar to a Fender amp. Replacing the .022µF cap at C34 with a .001µF gave a subtly tighter rhythm crunch, more similar to a Marshall. And to finish it off, I removed the 100pF cap at C47 to bring the rhythm tone stack closer to standard Marshall values.
I was already happy with the lead channel, but I went ahead and did some mods to it too “while I was still under the hood.” Most of these are either specs from the original 5150 or Soldano SLO100. I started off by replacing the 470pF cap at C5 with a 470KΩ resistor and a .0022µF cap in parallel, which is the spec for the original 5150. This gives a rounder, fatter bottom. I then replaced the .001µF cap at C26 with a .022µF, for much of the same reason. Replacing the 37.4KΩ resistor at C12 with a 39KΩ also brought me to SLO/5150 spec. Last, I swapped the 33KΩ resistor at R25 with a 47KΩ resistor and two 330pF capacitors in parallel (which is the exact same as a 47KΩ resistor and a 660pF cap in parallel, if you're curious). This thickened up the mids a bit, resulting in a less-scooped sound, while also cutting some of the fizz out.
Today I took it a step further, and went about replacing the 6.8nF caps at C37 and C74 with .01µF caps, thus lowering the range of the resonance controls by roughly an octave, which opened up the EQ a bit in both channels. I then replaced the 2.2KΩ resistors at R52 and R53 with 2KΩ resistors, yielding a slightly hotter bias in V1B and V2A, which affect the rhythm channel. This sweetened things up a hair. I also replaced the 220KΩ resistor at R14 with a 200KΩ to cause the power tubes to run a little hotter.
THE VERDICT: It's a game changer. I actually have a working clean sound, and it's much more sensitive to changes between guitars, pickups, coil splits, etc. It's not quite sparkling Fender clean, but is very serviceable, and with chorus, reverb, et cetera, it can be very nice (bear in mind I've only demo'd it dry at this point). The crunch sound is very Marshall-esque, and lends itself very well to classic rock and blues (neck or middle position with a Tele is where it's at!!!) and some of the semi-driven stuff I do in my own music (which is alternative rock/metal). The lead channel sounds rounder, with thicker mids and not as brittle or fizzy, and thus not so metal; however, still has more than enough gain on tap for metal, and I'd bet it'd still LOVE EMGs.
Overall, it took me a total of four hours of work spread out over two days. In my opinion, with the right tools and about $25 in components, it's definitely worth it. It still has the 5150/6505 sound, but it's much more versatile like this. It feels more like a tube amp, without all the extra fizz from the preamp and a slightly hotter bias on the tubes.
For tubes, I'm using a JJ 5751 in V1, Sovtek 12AX7LPS in V2, JJ ECC83S (12AX7) in V3 and V4, and a JJ ECC832 (12DW7) in V5. I haven't changed power tubes yet (still on the stock Ruby 6L6GCs), that will be next week when I grab some JJ 6L6s for that.\
As I did not develop these mods, these values on caps and resistors are not set in stone. A lot of them are within a suggested range by those who did develop them. For more information you can go here: http://atomiumamps.tumblr.com/post/9393 ... -6505-mods. He's a lot more detailed about this. While you're at it, Google schematics for both the 5150II head and 6505+ 112 combo, these would also be useful. Again, thank you for your help and info and I hope to hear from you soon!!