Plexi please.....
Plexi please.....
Next, as I dig deeper and deeper into this rabbit hole of building my own versions of virtually unobtainable amps...this one's gonna be like a 1968/1969 era 100 watt Plexi. Without getting too deep into the details, this time period of Marshall Plexis is kind of like the holy grail period. From their birth in 1962, the amps changed from year to year as Marshall tweaked the formula and somewhat just used what they had available. Through some intention and some dumb luck, around mid 1968 they seemed to land on the magic formula. This amp will be an attempt to recreate that the best I can with commercially available modern parts made to those old school specs. This will also be built with heavy duty live and recording use in mind. This is not a kit, there are no instructions. I'm using ancient scrolls, cave hieroglyphics, and hand drawn schematics from the 60s to make my own best interpretation.
Anyway, here we go.
I ordered a gorgeous stark white/gold Plexi style headbox from Sourmash about two months ago. The chassis and face plates are from Mojotone.
And here's the small parts. All the best I could get with a nod to how it was done in the olden days. Carbon film resistors, too-expensive Sozo mustard caps, F&T filter caps, custom Heyboer transformers and choke, making my own board, Belton tube sockets, etc.
Stay tuned....
Anyway, here we go.
I ordered a gorgeous stark white/gold Plexi style headbox from Sourmash about two months ago. The chassis and face plates are from Mojotone.
And here's the small parts. All the best I could get with a nod to how it was done in the olden days. Carbon film resistors, too-expensive Sozo mustard caps, F&T filter caps, custom Heyboer transformers and choke, making my own board, Belton tube sockets, etc.
Stay tuned....
Rebel Yell
Re: Plexi please.....
wow ... nice stuff ... hundred bucks just in yellow caps !
THIS is gonna be a killer
THIS is gonna be a killer
Re: Plexi please.....
I look forward to following the build. I was watching the Guitaristas last night - he was trying to dial in a "Bluesbreaker" 2003 re-issue. To get close to Clapton's Beano tone he had to use an attenuator as they beast had to be loud to get the breakup - he was still hovering around 97dBs when he was close. 2x12 40w combo at 30Kg/70lb and it needs the two channels to be on 8 & 5 to break up.
Not a great option really.
Not a great option really.
Cheers
rayc
rayc
Re: Plexi please.....
Well those amps were the first Marshalls and they are essentially Marshall's version of the tweed era 5F6 Fender Bassman. It's not designed to break up easily. It's technically a bass amp. And fun fact! As local british guitarists demanded more and more in those early days, and Marshall amps progressed and got tweaked and turned into Super Leads, those original "Bluesbreaker" circuits stayed in production, virtually unchanged, under the name....Super Bass.rayc wrote: ↑Fri Sep 22, 2023 7:43 pm I look forward to following the build. I was watching the Guitaristas last night - he was trying to dial in a "Bluesbreaker" 2003 re-issue. To get close to Clapton's Beano tone he had to use an attenuator as they beast had to be loud to get the breakup - he was still hovering around 97dBs when he was close. 2x12 40w combo at 30Kg/70lb and it needs the two channels to be on 8 & 5 to break up.
Not a great option really.
The thing I'm building here is about three iterations later of that same circuit. What I'm building is a Super Lead. Mine will differ from the Bluesbreaker/Super Bass in a few significant ways. More on that later.
Lol it wasn't easy buying those caps. I've been very pleased with the cheaper-yet-same Mallory 150s in my other Marshalls. But in the grand scheme of things they're not that expensive and I figured what the hell. A few extra bucks to try them out. If ever there was an amp to use them on, I think it's this one.
Rebel Yell
Re: Plexi please.....
I'm as excited about the white tolex enclosure as I am about the actual guts of this amp-to-be!
Re: Plexi please.....
Dude when I pulled that thing out the box...I was like wow this is awesome. It's pretty elegant looking. A nice juxtaposition to the horrible racket that will come out of it.
Rebel Yell
Re: Plexi please.....
no doubt .... that cab is spectacular!
Better get a cover for this one man ..... that's gonna mark up so easy no matter how careful you are with it.
also that head really needs a stark white speaker cab to sit on
Re: Plexi please.....
I expect this white box to get some scuffs pretty quick and that's okay. I don't mistreat my equipment but I do use it and using it means things happen. All of my heads and cabs have scuffs and rips on them.
But yeah I might get a cover for it. I don't have any amp covers. Won't hurt to get a few I guess.
Rebel Yell
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Re: Plexi please.....
This is cool as hell. That head box is friggin beautiful. Love that.
So is this your first piece meal attempt amp where you figure it all out yourself sort of thing. Or have you done another one with the sourcing all the bits?!
Looking forward to following this one.
So is this your first piece meal attempt amp where you figure it all out yourself sort of thing. Or have you done another one with the sourcing all the bits?!
Looking forward to following this one.
Re: Plexi please.....
No the Tender Assman and the "spite build" JCM 800 2204 were both done by sourcing all the bits and just figuring it out. They were not kits either.WhiskeyJack wrote: ↑Sun Sep 24, 2023 3:02 pm This is cool as hell. That head box is friggin beautiful. Love that.
So is this your first piece meal attempt amp where you figure it all out yourself sort of thing. Or have you done another one with the sourcing all the bits?!
Looking forward to following this one.
This is the first one where there is no real definitive schematic though. I'm physically building it as if it's a standard 100w Super Lead, as in, standup power transformer, external filter caps, typical Marshall Super Lead stuff. There are only three actual schematics that I can find that apply to this - the original late 50s 5F6 Bassman which these amps were originally based on, a 1967-ish hand drawn Marshall schematic that includes some errors, and an official 1970 Marshall 1959 Super Lead schematic. That 1970 one is pretty key to what I'm doing. It's the basic circuit I'm using. But I'm substituting some of the parts values for what I've learned from research and looking at pictures of actual 1968/1969 amps. Even though there's no schematic (that I can find) for a "1968 Marshall" enough people have dug through them by now that the information is out there. I'm just piecing it all together. I'm gonna build it like the 1970 schematic but substitute in the 1968 spec values. The 68/69 era circuits are kind of like "transitional" years for the amps. Some of it is still Bassman/JTM45-ish, and some of it is clearly headed towards the more aggressive sounding amps of the 70s. I'm trying to accurately straddle that line.
Rebel Yell
Re: Plexi please.....
Do you use a breadboard or anything to work through the circuit designs before committing to them by soldering and clipping off excess leads?
I've often thought of getting a breadboard to try and fiddle with the much safer low voltages of stomp box circuits. It'd be cool to learn the classic circuits and experiment with them.
I've often thought of getting a breadboard to try and fiddle with the much safer low voltages of stomp box circuits. It'd be cool to learn the classic circuits and experiment with them.
Re: Plexi please.....
you really should .... that thing's pretty man ....and it's doesn't take that long to throw a cover on plus you make up the time cause you don't have to be quite as careful.
My custom covers place does really nice covers.
Re: Plexi please.....
No I haven't. For one...I don't have a breadboard. The amp is the breadboard. And I don't think there are too many things that you could or would want to do without the amp actually being mostly assembled. The voltages in a functioning guitar amp are pretty big and very little of it could be isolated on a breadboard. Secondly, I'm not reinventing the wheel here. Most of the stuff I mess with is scientifically and functionally already proven. But to your point I do often "temp" in parts and pieces with jumper wires to test them out before final soldering. Lots of alligator clips and jumper wires makes it pretty easy to do some experimenting. And if necessary a quick tack-solder can hold something in place just for testing and then get a proper solder later.
That's probably what breadboards are best suited to. You can pretty easily lay out a pedal design on a breadboard and play with different values...and not electrocute yourself in the process. Win/win. If I was a pedal guy I'd be breadboarding all day long.I've often thought of getting a breadboard to try and fiddle with the much safer low voltages of stomp box circuits. It'd be cool to learn the classic circuits and experiment with them.
Rebel Yell
Re: Plexi please.....
Back at this thing...been waiting on a few extra parts and getting done with other shit.
Anyway, the worst is over. All the fitting, bolting, securing, and wiring the heaters is done.
Monster transformers. This thing is heavy already. Stainless hardware and lots of loc-tite holding it all together.
You've seen this before. It never gets easier. The heater wiring.
This is something that's pretty common on other amps (like Fenders) but you don't often see it in Marshalls. This is a little artificial balanced center tap I created for the heater wiring. It's got a 100 ohm resistor to ground on each leg of the filament wiring. Usually the center tap is a separate wire halfway between the heater winding and it goes directly to ground. That's fine, no problem. When it is a problem is if the heaters short to a plate or cathode in a tube then you nuke the power transformer with a short to ground through the filament winding. These little 100 ohm resistors will act as makeshift fuses while also providing the perfect balance between the two halves of the heater winding. Necessary? No. But a little insurance and maybe a slight improvement in heater noise potential. I'll cap off the normal center tap wire and leave it disconnected.
Next will be stuff around the tube sockets and rear panel.
Anyway, the worst is over. All the fitting, bolting, securing, and wiring the heaters is done.
Monster transformers. This thing is heavy already. Stainless hardware and lots of loc-tite holding it all together.
You've seen this before. It never gets easier. The heater wiring.
This is something that's pretty common on other amps (like Fenders) but you don't often see it in Marshalls. This is a little artificial balanced center tap I created for the heater wiring. It's got a 100 ohm resistor to ground on each leg of the filament wiring. Usually the center tap is a separate wire halfway between the heater winding and it goes directly to ground. That's fine, no problem. When it is a problem is if the heaters short to a plate or cathode in a tube then you nuke the power transformer with a short to ground through the filament winding. These little 100 ohm resistors will act as makeshift fuses while also providing the perfect balance between the two halves of the heater winding. Necessary? No. But a little insurance and maybe a slight improvement in heater noise potential. I'll cap off the normal center tap wire and leave it disconnected.
Next will be stuff around the tube sockets and rear panel.
Rebel Yell
Re: Plexi please.....
You're gonna end up like that Dumble guy... rich!
- WhiskeyJack
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Re: Plexi please.....
Gerk, that just LOOKS awesome man. It is one thing to have a good working knowledge of this shit, but you even make it look good. Good stuff buddy. I veyr much hope one day i can own a Greg™ amp.Greg_L wrote: ↑Wed Oct 04, 2023 3:52 pm Back at this thing...been waiting on a few extra parts and getting done with other shit.
Anyway, the worst is over. All the fitting, bolting, securing, and wiring the heaters is done.
Monster transformers. This thing is heavy already. Stainless hardware and lots of loc-tite holding it all together.
You've seen this before. It never gets easier. The heater wiring.
This is something that's pretty common on other amps (like Fenders) but you don't often see it in Marshalls. This is a little artificial balanced center tap I created for the heater wiring. It's got a 100 ohm resistor to ground on each leg of the filament wiring. Usually the center tap is a separate wire halfway between the heater winding and it goes directly to ground. That's fine, no problem. When it is a problem is if the heaters short to a plate or cathode in a tube then you nuke the power transformer with a short to ground through the filament winding. These little 100 ohm resistors will act as makeshift fuses while also providing the perfect balance between the two halves of the heater winding. Necessary? No. But a little insurance and maybe a slight improvement in heater noise potential. I'll cap off the normal center tap wire and leave it disconnected.
Next will be stuff around the tube sockets and rear panel.
Re: Plexi please.....
man you do good work .... keep it up so when I croak my wifey'll have two of the earliest gergamps to sell at inflated prices
Re: Plexi please.....
Well if she can't sell them for huge prices they can always come back here with me.
WhiskeyJack wrote: ↑Wed Oct 04, 2023 8:13 pm
Gerk, that just LOOKS awesome man. It is one thing to have a good working knowledge of this shit, but you even make it look good. Good stuff buddy. I veyr much hope one day i can own a Greg™ amp.
Thanks gents. Yes it does look pretty when things are tidy and organized. It looks like care was taken and it looks like high quality. But I've said it before...it's functional. Tidy clean wiring usually means mistake-free wiring. That's far more important than looking good. I need the amps I build to work and work hard and work flawlessly. I probably go a little overboard. I'm not on a schedule and I don't let anything slide. I just want it to be as perfect as I can do. No second guessing anything.
Rebel Yell