1987x PPIMV and Cascade Mod - help please!

[Greg_L]

Hi, I'm new here. I didn't see an introduction section, so I figured I'd jump right in.

Okay, I got this 2001 1987x here. No effects loop. Basic 50w Plexi reissue. Cool.




I want to add a PPIMV so I can then try the "one wire" cascaded gain mod...and hopefully make it switchable somehow.

I will need help. I've worked on amps before with guidance. I know the safety protocols, how to solder, etc. I do not know the parts, names of parts, what they do, or why they work, but if you guys can show me the way, I can do it.

So first up, the PPIMV. I have a Triode PPIMV kit.
First question...what resistors do I need to remove? I think they're the one's I've circled in yellow. Please advise.




Second question...in that same pic above ^^^^ I've circled in red the wires I need to remove from the power tube pins. I've researched to find that people install 5.6k "swamp resistors" in those spots and then the leads to the PPIMV pot. Is this correct? Are swamp resistors necessary? My kit does not include them and they are not on the amp stock. I can get some though, no problem. What do they do, and do I need them?

Please help me with these two starter questions so I can get this thing going. I've done my research and searched threads all over the internet and think I have it figured out, but some personalized guidance would be appreciated.

Thanks.

[martin manning]

Looks like you've ID'd the 220k grid leak resistors that will be replaced by the dual MV pot correctly. The addition of grid stoppers (aka swamp resistors) will help prevent oscillations, and I'd definitely add them since you will be have some long leads running to the MV. You'll want to remove the orange and green leads that connect to the pin 5's on the power tube sockets completely, unless you use them to carry the audio signal to the MV pots. That would be my preference, and I think you could do this without lifting the board. Just disconnect them from the tube sockets and twist them together, splicing on some additional length as needed. For the bias voltage you can solder a lead to one of the 220k's and take that to the bottom of both MV pots, then lift the other end or clip out both 220k's to get them out of the circuit.

[Greg_L]

Looks like you've ID'd the 220k grid leak resistors that will be replaced by the dual MV pot correctly. The addition of grid stoppers (aka swamp resistors) will help prevent oscillations, and I'd definitely add them since you will be have some long leads running to the MV. You'll want to remove the orange and green leads that connect to the pin 5's on the power tube sockets completely, unless you use them to carry the audio signal to the MV pots. That would be my preference, and I think you could do this without lifting the board. Just disconnect them from the tube sockets and twist them together, splicing on some additional length as needed. For the bias voltage you can solder a lead to one of the 220k's and take that to the bottom of both MV pots, then lift the other end or clip out both 220k's to get them out of the circuit.

Hey thank you martin for the reply. Seems like I'm on the right track then. I picked up some 5.6k swamp resistors today at one of the few remaining Radio Shacks in existence, so I've got everything I need....I think.

I've already lifted the board to remove the resistors properly, so I'm neck deep into that. I will be removing those green/orange wires and replacing them with shielded cable.

The Triode kit I've ordered has the pot, 2.2meg resistors, and shielded cable. All I had to pick up were the swamp resistors, so I think I'm good to go for the PPIMV. Fingers crossed!

[Stevem]

Why is it you want a master volume in the amp?

[Greg_L]

Why is it you want a master volume in the amp?

Because I don't always want to use an attenuator. I have one I'm happy with, Weber Mass 200, but I don't always want to take it out to shows.

I play punk rock gigs and some of them are sort of rough and tumble and some of them are in somewhat shady venues. Volume control and one less piece of gear to carry around/get knocked over is a win in my book.

The PPIMV is installed and perfectly functional.

[ampmike]

I think there is a you tube vidio under master vol Marshall. Try searching that. You got the right info from the best guy here but this might help just seeing it done.

[Greg_L]

I think there is a you tube vidio under master vol Marshall. Try searching that. You got the right info from the best guy here but this might help just seeing it done.

Thanks for the reply. It's actually been done for a few weeks now and working perfectly.

[ampmike]

Awesome man!!!!!Im building a metro plexie 50.Going slow but I might message you because Ill probably want a MV,Have fun