I've been playing my build for a few years now and have really enjoyed it but I'd like a little more flexability and decided to do a couple of mods over the winter. The first one is complete. I already had a Lar-Mar PPIMV but still had to use an attenuator to get my lead volume (bypass the attenuator when playing leads). So I did the dual PPIMV mod and made it footswitchable.
Next I want to try the Neil Special 2-in-1 Mod to switch between the Plexi and JCM800. I can't find the 1M push pull pot in the US and I'm wondering if I could use the same footswtich realy set up that I use for the PPIMV to swtich between the two channels. I think it would work but I'm not 100% sure. Can you guys look it over and let me know if you think it will work? Another option would be to use a 1M pot and a DPDT switch both on the front of the amp.
12 Series mods
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Tone_Chaser
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12 Series mods
Barry
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Tone_Chaser
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Re: 12 Series mods
This is the layout for the footswitch for the dual PPIMV.
This is the dual PPIMV switching relay layout.
This is a quick layout I did showing how I think the relay would be wired. The switch connections are labelled with the corresponding connections on the relay. Please let me know if you think this will work Thanks!
- Dual%20PPIMV%20R2.JPG (87.89 KiB) Viewed 2060 times
- Channel Sw.jpg (102.28 KiB) Viewed 2060 times
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Tone_Chaser
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Re: 12 Series mods
Not sure what I did, but the 13 on the switch should be 11 and the 18 should be 13. 
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julkke
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Re: 12 Series mods
Yep you could do the 2 in 1 via relay but the volume difference between the modes might be too much and you might get a pop when switching. The pop issue is covered somewhere here though. I would just put a normal dpdt switch to do it if you don't need to be able to footswitch.
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neikeel
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Re: 12 Series mods
Yes it will work but with shared plexi volume and cascaded gain pot will likely give a volume boost. Of course you may want this, but using separate pots is what I prefer so you can balance it out.
I tend to switch mine between songs when the pop is not an issue.
I tend to switch mine between songs when the pop is not an issue.
Neil
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Tone_Chaser
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Re: 12 Series mods
I want to use the separate volumes like the Neil speacial version. I just can't find the pot in the US, there are a number of 500K pots but no 1M pots. Instead of doing a push-pull pot I could remove two input jacks and install a 1M pot in one and the DPDT switch in the other and switch it that way.
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julkke
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Re: 12 Series mods
Do it like that if you want! 
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neikeel
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6burgh
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Re: 12 Series mods
yup... Neil beat me to it. I've used this pot for numerous different applications. Works great, you may notice the difference in the physical "stiffness" when turning the pot. These are much looser and easier to turn than say alphas.
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Tone_Chaser
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Re: 12 Series mods
Thanks guys, I just found that same pot today at tubesandmore.com and I think that's the way to go. I would prefer pins with holes that are easier to solder wire to but I think this is the best option for me.
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Tone_Chaser
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Re: 12 Series mods
This thread was intended to be a living thread that I would use when I would try out some new mods so here is my new mod adventure.
First, an update of where I am now. I did end up doing the 2-in-1 mod and only played one gig with it and didn't like it. We had a lot of jobs coming up and didn't have enough time to play with it so I went back to my original Plexi design. It's not stock by any means, I used some of the basic mods when I built it, lowered filtering caps, etc. I can do some checking and list the changes from stock if necessary because I'm going to be asking for some opinions on what I want to do next.
I haven't touched the insides in about three years, since the last posts in this thread. I've just been playing it and I really do like the sound but I've been GASing for that hot rodded Marshall sound that I hear on You Tube from amps like the Friedman, Cameron, Fortin, etc.
I thought about building a version of the BE100 using the schematic that's floating around because I love that sound and that it has a really nice clean channel, but it would take me a year or more to come up with the money to build it while also building guitars and pedals.
Then I thought about trying a new version of the 2-in-1 mod to my amp. What if I did the mod to switch between the Plexi and a hot rodded Plexi instead of the JCM800?
I have a couple of months before I need the amp again due to two of the band members having surgery over the next few weeks and the first couple of jobs back will be covered with the JTM45 combo I built. This will give me some time to make changes here and there and evaluate each change.
The first thing I'm going to do is put the POT back in with the push/pull switch to change between the two sounds so I can cascade the modded channel. Instead of using the top hole, I want to use the bottom hole for the POT. Most people use the top input and that's the sound that works best for me on the bright channel.
Since I'm going for the modded Plexi instead of the 800, I'm thinking about using another 2.7k/.68uf combo on the V1a cathode instead of the 10K used in the 800. I'm also thinking about leaving out the 470K/470p between the input and gain POT. This is on the 800 schematics, but not on the hot rodded schematics I see.
I'm looking forward to working on this and getting some input from you guys. You are such a great resource!
First, an update of where I am now. I did end up doing the 2-in-1 mod and only played one gig with it and didn't like it. We had a lot of jobs coming up and didn't have enough time to play with it so I went back to my original Plexi design. It's not stock by any means, I used some of the basic mods when I built it, lowered filtering caps, etc. I can do some checking and list the changes from stock if necessary because I'm going to be asking for some opinions on what I want to do next.
I haven't touched the insides in about three years, since the last posts in this thread. I've just been playing it and I really do like the sound but I've been GASing for that hot rodded Marshall sound that I hear on You Tube from amps like the Friedman, Cameron, Fortin, etc.
I thought about building a version of the BE100 using the schematic that's floating around because I love that sound and that it has a really nice clean channel, but it would take me a year or more to come up with the money to build it while also building guitars and pedals.
Then I thought about trying a new version of the 2-in-1 mod to my amp. What if I did the mod to switch between the Plexi and a hot rodded Plexi instead of the JCM800?
I have a couple of months before I need the amp again due to two of the band members having surgery over the next few weeks and the first couple of jobs back will be covered with the JTM45 combo I built. This will give me some time to make changes here and there and evaluate each change.
The first thing I'm going to do is put the POT back in with the push/pull switch to change between the two sounds so I can cascade the modded channel. Instead of using the top hole, I want to use the bottom hole for the POT. Most people use the top input and that's the sound that works best for me on the bright channel.
Since I'm going for the modded Plexi instead of the 800, I'm thinking about using another 2.7k/.68uf combo on the V1a cathode instead of the 10K used in the 800. I'm also thinking about leaving out the 470K/470p between the input and gain POT. This is on the 800 schematics, but not on the hot rodded schematics I see.
I'm looking forward to working on this and getting some input from you guys. You are such a great resource!
Barry
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Tone_Chaser
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Re: 12 Series mods
Since I decided to do some mods I've been going through this section to see what mods have been talked about and I made a list of mods and ordered all of the parts to do all of them, knowing I probably wouldn't use most of the parts. But I wanted them available in case I want to keep going. My plan is to do one mod at a time and evaluate it and decide if I want to change that mod, leave it as it is or do another mod.
The parts came in this week so I got started. Mod #1 for me is the Neil Special 2-in-1 and having it switch between Plexi and Modded Plexi instead of 2203.
I finished the mod today (I really feel like I'm using the word "mod" a lot!) I installed the POT/switch and wired everything up and replaced the 820/330 combo with the 2.7K/.68 combo and a 68K in place of the 470K/470p combo.
I plugged it in tonight and my bright channel operates as it had before (YAY!) but when I pull out the POT with both of the cascaded volumes cranked and the PPIMV all the way up, I get sound but no gain and it isn't very loud.
Looks like I get to go over every change and make sure it matches the layout so I can find my mistake. I was hoping it would work great the first time but I'm not really surprised it didn't.
I'll update when I find out what I did wrong.
The parts came in this week so I got started. Mod #1 for me is the Neil Special 2-in-1 and having it switch between Plexi and Modded Plexi instead of 2203.
I finished the mod today (I really feel like I'm using the word "mod" a lot!) I installed the POT/switch and wired everything up and replaced the 820/330 combo with the 2.7K/.68 combo and a 68K in place of the 470K/470p combo.
I plugged it in tonight and my bright channel operates as it had before (YAY!) but when I pull out the POT with both of the cascaded volumes cranked and the PPIMV all the way up, I get sound but no gain and it isn't very loud.
Looks like I get to go over every change and make sure it matches the layout so I can find my mistake. I was hoping it would work great the first time but I'm not really surprised it didn't.
I'll update when I find out what I did wrong.
Barry
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neikeel
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Re: 12 Series mods
What happens with master and gain on 5 (with PPIMV all way up)?Tone_Chaser wrote:Since I decided to do some mods I've been going through this section to see what mods have been talked about and I made a list of mods and ordered all of the parts to do all of them, knowing I probably wouldn't use most of the parts. But I wanted them available in case I want to keep going. My plan is to do one mod at a time and evaluate it and decide if I want to change that mod, leave it as it is or do another mod.
The parts came in this week so I got started. Mod #1 for me is the Neil Special 2-in-1 and having it switch between Plexi and Modded Plexi instead of 2203.
I finished the mod today (I really feel like I'm using the word "mod" a lot!) I installed the POT/switch and wired everything up and replaced the 820/330 combo with the 2.7K/.68 combo and a 68K in place of the 470K/470p combo.
I plugged it in tonight and my bright channel operates as it had before (YAY!) but when I pull out the POT with both of the cascaded volumes cranked and the PPIMV all the way up, I get sound but no gain and it isn't very loud.
Looks like I get to go over every change and make sure it matches the layout so I can find my mistake. I was hoping it would work great the first time but I'm not really surprised it didn't.
I'll update when I find out what I did wrong.
Have you wired the inputs correctly?
If you are still having issues post some pics.
Neil
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Tone_Chaser
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Re: 12 Series mods
When I was finishing up, my phone rang and when I came back to finish I didn't look at the diagram again and wired the bottom two wires on the switch backwards.
I swapped them like they should be and I get much more gain this time. I've only had a few minutes to test it and it squeals quite a bit on the mod channel so I'm going to put it back in the cabinet with the shield plate in it and see if that takes care of the noise. If not, I'll go from there. I won't have time to mess with it until tonight thought.
I swapped them like they should be and I get much more gain this time. I've only had a few minutes to test it and it squeals quite a bit on the mod channel so I'm going to put it back in the cabinet with the shield plate in it and see if that takes care of the noise. If not, I'll go from there. I won't have time to mess with it until tonight thought.
Barry
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neikeel
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Re: 12 Series mods
Careful lead dress will help and in the cab.Tone_Chaser wrote:When I was finishing up, my phone rang and when I came back to finish I didn't look at the diagram again and wired the bottom two wires on the switch backwards.
I swapped them like they should be and I get much more gain this time. I've only had a few minutes to test it and it squeals quite a bit on the mod channel so I'm going to put it back in the cabinet with the shield plate in it and see if that takes care of the noise. If not, I'll go from there. I won't have time to mess with it until tonight thought.
Usual mods for PO (5k6 per output grid, shielded grid wire. Plate wires to chassis floor, grids raised away form plate wires as short as possible. My 50w version is rock solid.
Did you raise the gain from stock? If not you should be ok. Adding bypass caps to the cold stage 10k cathode, or lowering the 10k below 8k2 will mean a plate bypass cap on the second stage (500pF rated at 1kV ceramic)
Neil