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The Mother of All 6505+ 112 Mods!!!

Posted: Sat Mar 26, 2016 11:54 pm
by davidhenryguitar
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!!

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Wed Mar 30, 2016 12:29 am
by Tobaccosun
Great to hear someone else has followed the same steps I took a few months ago with mine. I too did all of the above mods and then some, added choke as well as some caps across pins on v4 and v5(an old 5150 mod trick) the amp definitely rocks much harder now and I made several of the mods switchable such as the tone stack mods and others that affect gain structure and or bright switches and fat switches(bottom end) spent about $20 in caps and resistors and switches, and 40 for choke from Mercury mag. I bought the amp for $100 on Craigslist and it was in perfect condition minus one bad preamp tube in v1 which made the guy think the amp had a problem hence the cheap price. I just retubed with JJ ecc83s and some new 6l6s and all good. Definitely check out atomium amps and Audun Melbye etc for mods as yes the 5150, 5150ii 6505+head are extremely similar in design and these are some very easy amps to mod cheaply but with a huge tonal improvement! Happy modding!!

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Thu Mar 31, 2016 1:52 pm
by davidhenryguitar
Tobaccosun wrote:Great to hear someone else has followed the same steps I took a few months ago with mine. I too did all of the above mods and then some, added choke as well as some caps across pins on v4 and v5(an old 5150 mod trick) the amp definitely rocks much harder now and I made several of the mods switchable such as the tone stack mods and others that affect gain structure and or bright switches and fat switches(bottom end) spent about $20 in caps and resistors and switches, and 40 for choke from Mercury mag. I bought the amp for $100 on Craigslist and it was in perfect condition minus one bad preamp tube in v1 which made the guy think the amp had a problem hence the cheap price. I just retubed with JJ ecc83s and some new 6l6s and all good. Definitely check out atomium amps and Audun Melbye etc for mods as yes the 5150, 5150ii 6505+head are extremely similar in design and these are some very easy amps to mod cheaply but with a huge tonal improvement! Happy modding!!
I'm still new to amp mods, what does a choke do for the tone? Apologize in advance for the noob question.

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Sat Apr 02, 2016 7:25 pm
by Tobaccosun
davidhenryguitar wrote:
Tobaccosun wrote:Great to hear someone else has followed the same steps I took a few months ago with mine. I too did all of the above mods and then some, added choke as well as some caps across pins on v4 and v5(an old 5150 mod trick) the amp definitely rocks much harder now and I made several of the mods switchable such as the tone stack mods and others that affect gain structure and or bright switches and fat switches(bottom end) spent about $20 in caps and resistors and switches, and 40 for choke from Mercury mag. I bought the amp for $100 on Craigslist and it was in perfect condition minus one bad preamp tube in v1 which made the guy think the amp had a problem hence the cheap price. I just retubed with JJ ecc83s and some new 6l6s and all good. Definitely check out atomium amps and Audun Melbye etc for mods as yes the 5150, 5150ii 6505+head are extremely similar in design and these are some very easy amps to mod cheaply but with a huge tonal improvement! Happy modding!!
I'm still new to amp mods, what does a choke do for the tone? Apologize in advance for the noob question.
The choke replaces the big ugly green resistor and smooths out the power and will tighten up the amp a bit. One with 10 Henry's is the one I got from Mercury magnetics. You'll mount it under the open space between OT and pcb and run the leads to (R13 I think) you'll also need to relocate the standby switch to the b+ side or else you'll get a loud pop every time you switch on and off. There's a thread that shows step by step. By user evad5150 https://www.ultimate-guitar.com/forum/a ... -p-12.html

On another note I have to say, I love the rhythm crunch channel on it most with maxed gain and the lead channel with gain only at 3 or 4 any more sounds like overkill and less punchy on the bottom end and becomes flubby mess :( as much as I enjoyed working on it and studying the 5150 and 6505's diagrams to compare and try stuff out I'm now selling the amp because I got a Framus Dragon version 1 and it kills every amp I've ever played, marshals, mesa's, peavey's etc... And that says a lot. I'd like to keep my 6505+112 and mod to a head only so I can set them up in stereo with my guitar signal with a Radial Engineering Big Shot A/B/Y switcher cause I think they'd compliment each other, but I'd rather sell it and get some pedals or other gear. It will be a sad day when it leaves because I really enjoyed working on it to make it what it is now:( even my 8 yr old said "sell it? Bit why?? You worked so hard on it making it more awesome..." Haha my kid is awesome!

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Sat Apr 02, 2016 7:47 pm
by Tobaccosun
Oops I meant r7 NOT R13. Apologies.

Separate mod, Cutting r13 gives a huge big bottom end to the clean channel. Crunch is not affected. I loved it because I use my volume knob on guitar to adjust the end tone.

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Wed Apr 06, 2016 11:35 pm
by davidhenryguitar
Tobaccosun wrote:Oops I meant r7 NOT R13. Apologies.

Separate mod, Cutting r13 gives a huge big bottom end to the clean channel. Crunch is not affected. I loved it because I use my volume knob on guitar to adjust the end tone.
Cutting R13 was one of the first things I did. Made a night-and-day difference.

Expanded 6505+ 112 Modding Research...

Posted: Sun Jun 05, 2016 11:30 pm
by davidhenryguitar
Ok so I decided to mod the Lead Channel to match the Lead Channel of the original 5150 to a T. Definitely gave a looser, more bassy feel (which is a good thing). It's actually laid out identically, but a few caps and resistors need to be changed. These values have come straight from a block letter schematic. Here's what you do:

THESE SO FAR HAVE ALREADY BEEN COVERED BY MANY:
1) Replace the 470pF capacitor at C5 with a .0022μF capacitor and a 470KΩ resistor in series. Makes for a rounder, looser feel.
2) Replace the 1nF capacitor at C26 with a .022μF capacitor. Brings back more low end.
3) Replace the 37.4KΩ resistor at R12 with a 39KΩ resistor.

HERE IS WHAT I FOUND ON THE ORIGINAL 5150 SCHEMATIC:
1) Replace the 10KΩ resistor at R9 with a 22KΩ resistor.
2) Replace the 82KΩ resistor at R32 with a 470KΩ resistor.
3) Replace the 10nF capacitor at C27 with a jumper.
4) Add a 10nF capacitor in series with the 47KΩ resistor at R46, opposite the ground.
5) Add a 100pF capacitor in parallel with the 470pF capacitor at C1. Shifts treble band downward and brings out more upper mids.
6) Replace the .22μF capacitor at C28 with a .1μF capacitor and .033μF capacitor in parallel. This changes the frequency of the presence control. C28 works with both presence pots. I have yet to do this particular mod, due to time constraints.

FURTHERMORE...
This is where I'm at. Partly inspired by the voicing switch on my old Randall RH150G3 head, I plan on installing scoop switches to both channels. The switch on the Randall lowered the frequency of your mid control and gave more of a scooped sound with more high mids and brightness, but with adjusting the bass knob accordingly actually made your tone chunkier and tighter. Using the Marshall tonestack on Duncan's Tone Stack Calculator (which is very helpful in simulating how different components will shape the tone) I have found that R47 (lead) and R26 (rhythm), or alternatively C40 (lead) and C42 (rhythm) are what will most directly affect the center frequency of the mid band.

Let's look at the lead channel. R46 is a 47KΩ resistor, and using it with the above mods (with all EQ set to noon) will bring your center frequency to roughly 500Hz. But add a 68KΩ resistor in series (giving you 115KΩ total) and that frequency drops to +/-350Hz, which brings the bass frequency down and drops bass and mids as a whole about 2.5-3dB. Obviously, you still have half the travel of your bass pot (and about 2/3 of the resistance left due to the audio taper), so you can in most cases dial what low end you need back in. A simple SPST toggle switch could switch said 68KΩ resistor in and out, so people could choose between stock mode and scooped mode. This could also help create better cleans in the rhythm channel, by giving it that Fendery V-shape in the mids.

Another way to do this is to add a capacitor in parallel with C40 or C42. It would also drop the center frequency and gain of the mid bands. For example, with a .022μF cap at C40, you have a center of about 500Hz. Add a .047μF cap in parallel (making .069μF) and that frequency shifts down to around 300Hz, although it doesn't scoop as dramatically as it does when manipulating R46. I don't see this as making as radical of a difference though.

ON TOP OF THAT...
Anyone else put off by the presence control only working from 8-10? Because I surely am. We've referenced the stuff that Matt Weed of Atomium Amplification has been doing to 5150/6505 series amps. One thing he mentioned in his blog is it is all in the taper of the pot (in this case, VR13 and VR15 are 10KΩ audio pots), and that in this case, a reverse-audio or linear pot would work better. In fact, the Marshall JCM800 2203 uses a 22KΩ linear pot for presence. I actually plan to replace those two with 20KΩ linear PC-mount pots (the ones that come in newer Marshalls, like the JCM2000, with 4 pins and side latches are direct drop-ins for this amp--AES carries them). I suggested above to replace the .22μF cap at C28 with a .1μF and .033μF in parallel (which gives .133μF), but that is only in keeping with the 5150 spec. I haven't done this mod yet, but when I do, I think I'm just rolling with .1μF to go with the 20KΩ pots (which is the actual 2203 spec +/-10% resistance).

Here's another finding on the mid control on the lead channel. It's a 50KΩ linear pot with a 47KΩ resistor (R48) in parallel (yielding around 24KΩ total resistance). On paper this works to get closer to a 25KΩ pot, but instead the parallel resistor just messes with the taper of the pot, and makes the control not as usable as it should be. I may use another 20KΩ for this as well, and do away with R48 altogether.

Feel free to chime in on whatever ideas you guys can think of as well, and try these ideas/suggestions on your own and let me know how/if it works for you!

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Sun Aug 07, 2016 10:21 pm
by chryssid
hello david henry guitar, I made the change in preamp of my 6505 112, in the rhythm of the channel, to be equal to 5150 II, because I have one and I would both stay with the same sound, but I make changes of components only between the tube and pots of eq, however the rhythm cannal got the much lower volume than the lead channel, for example, the rhythm in volume 5, is equal to, lead volume 2, you have any suggestions to give me, to both have the same volume,? Because the rhythm with this very low volume compared to lead, and I miss the volume when using the amp with the band.

I used these schemes, I modified all values of c31 to r8, that sounded like 5150 II with bright switch, activated,


http://www.thetubestore.com/lib/thetube ... ematic.pdf

http://www.thetubestore.com/lib/thetube ... ematic.pdf

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Tue Jun 27, 2017 1:53 pm
by epilespaulgoth
Im new to the forum and an avid tinkerer. I did every mod to my 6505+ 112 to make it into a 5150 and its amazing. A bit harder for me to dial in the mids without them getting to harsh. I would love o know what settings to use on the lead channel to dial up a good hardcore tone something maybe august burns red like. Thanks for the great mods.

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Mon Jan 08, 2018 8:07 pm
by Shilgeman
Are these modifications true? Has anyone tried them?

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Sat Jul 11, 2020 12:01 am
by Uncle Scooter
I did these mods... and this in now 90% of what I was looking for in amp tone!!

Re: The Mother of All 6505+ 112 Mods!!!

Posted: Thu Apr 08, 2021 10:39 am
by cocoamousse
Hey everybody !

I'm just starting to mod my 6505+ combo, just to be straight when you're talking about removing a component it is actually removed, or by-passed (as in putting a jumper to keep the circuit as is) ?

Thanks for all the infos, that's great !