PLX wrote: ↑Mon Jun 06, 2022 1:11 pm
There is no way I can sit in a 10' x 11' room with a 100W amp with the master volume knob on 10.. and that's what will be required to run this amp in "plexi" mode.
Yeah I fully understand about the volume thing, my amp room isn't huge and even with two pulled power tubes, Rivera Rockcrusher, variaced to 70-80 VAC it can still fairly loud I won't claim its a "loud TV volume" because it isn't. It's comfortably tolerable compared to playing with a live band.
Your'e definitely not a hack...you've been at this as long as I have been. Your electronic build skills shows your're not. If you really really want true Ed tone I have to say a blasting 2 gain stage plexi circuit is what is needed. The cascaded circuit is not pummeling the PI maybe when it is cranked to degree. If you decide to retain the cascade you will have to be satisfied with close IMHO.
You have to remember if Ed was variacing down to the 70VAC range that would be why he needed to reamp with the Fender Bandmaster and other Marshall Superleads as you see onstage in the first leg of the 78 tour, Japan and the later leg of the 78 tour like at Selland arena. Also as he started playing bigger arenas he could crank the plexi's to get what he wanted and sheer volume control became less of an issue live but I would imagine some volume control was somewhat needed in the studio.
I've looked at your amp circuit pic, it this were my amp here's what I would. I you want to keep the cascade I would change it to a RT mod cascade that uses a Post Phase Inverter MV ala Lar/Mar from Metro. It is most plexi sounding of the cascade desgin that I have found and I did it to my 72 Marshall and it retains everything I like about my 68. I can send you the layouts of it if you wish. If you like the cascade setup you have here's what I would try... I also have layouts of the old Ralle cascade if you want them.
Is the 470K/500pf and 470K still invidual mixers for each channel or did you change it to a voltage divider ala 2203?
replace the Xicon box .022uf bax cap with a synergy Mustard
Replace the Sang/generic black Silver micas with either RS/Lemco mica 560pf or Brown 1980's NOS CDE silver micas on the tonestack and mixer cap
I can't remember what but Larry said they have issues later in life a generate noise or DC something along those lines.
I would replace the PI fizzy cap with a 47pf Lemco dogbone you can still get them from valvestorm and I think he has tan/orange CDE 560pf caps as well.
Install an actual Synergy .68uf cap on V2A regardless of what fat cap you decide to go with, it just makes a difference IMHO and Dave Friedman thinks so too. I have a .68 NOS mustard and a 25uf on my 68 Ed spec you still get some tonal effect of the .68uf while the fat cap passes more gain, it weird but there is a difference.
I can mail you two NOS CDE 560pf if you want them. Lotsa roads regarding Ed lore and I've driven alot of miles on them as well as you PLX!
I know your time if taken up with the AH-50 build so what I suggested may not be feasible. If you want any of those layouts hit me up.