• Guys, we've spent considerable money converting the Les Paul Forum to this new XenForo platform, and we have ongoing monthly operating expenses. THE "DONATIONS" TAB IS NOW WORKING, AND WE WOULD APPRECIATE ANY DONATIONS YOU CAN MAKE TO KEEP THE LES PAUL FORUM GOING! Thank you!

planning for Marshall Amp mod/conversion

BrianGWN

Great 'Double White' North ~ Electronics Specialis
Joined
Jul 15, 2001
Messages
1,401
>Marshalhead: ...or wound up to Jesus volume...<
Is that when people grab their ears and sort of recoil from the volume shouting "Oh Jesus!"?, or instead when the tone is so sweet and crunchy and singing and sustaining etc... that people sort sit back with eyes wide and quietly mutter "Oh man, Oh Jesus..."? :lol

RICH/Marshalhead, yep good stuff to keep in mind. Okay so maybe the way to proceed would be to first get the amp setup as close as possible to a stock Super Lead, front to back, and then maybe work from there. (update on a Jim Croce song: You don't tug on Superman's cape, you don't spit into the wind, you don't pull the mask off the ole Lone Ranger, and you don't mess around with Jim Marshall !)
It occurred to me that once you get some speaker cones moving in a closed back cabinet that should probably up the overall lower end "thump", so one shouldn't overlook the role of the choice of speakers and cabinet in the overall scheme.

Today I finally found what appears to be some good 500pf caps, and a few other caps of interest, so I think we finally have all the potentially required parts to do proceed with surgery. "Nurse, scrub the patient and prep her for a Bassectomy"...
 

Marshallhead

New member
Joined
Jul 19, 2001
Messages
5,556
BGWN My 69 SB measures about 550v at the plates and sounds great for clean tones down low which is why I wouldnt RICH that one. It really doesnt do the distortion well until like 8 on the volume which is heiniously loud. The lead circuit will start dirtying around 3 and up if healthy. With the RICH tweaks in place you can have nice dirt at "mouse fart volumes" and not burn tubes up every 6 months or less. His mods are easily the best sounding I have ever heard especially for a metal head like me who also appreciates the less distorted tones. You played his stuff so you know what I am talking about. I have an 81 2204 I am going to have him turn into the antichrist ASAP.

Enjoy that amp bro-Its an all time great-congrats:dude


BTW-Jesus volume when the floor is pounding so hard your legs are numb from the amp:lol
 

Sean

Goldie's Man in London
Joined
Jul 15, 2001
Messages
2,021
I can't be the only person who finds SLs too bright?

BG, I'd stick the RICH master in that thing and the couple of tweaks to pump up the gain, and check out what it sounds like through a 4x12, BEFORE I did the full SL mod.

I mean, you're going to those mods *anyway*, so why not do 'em first?
 
Joined
Aug 5, 2001
Messages
191
Doctor Brian has commenced work, I think he's converting it to a SL and then putting in the Rich mod but then you never know what he has up his sleeve.:dude
 

Ed Rafalko

Les Paul Forum Member
Joined
Jul 15, 2001
Messages
6,287
If there's a mushroom cloud over Canada in the morning, we'll know what happened.
 
R

RICH

Guest
Hmmm, I'll have to fire up the deathwall to blow the cloud back to canada should it decide to travel down here.:lol2
 
Joined
Aug 5, 2001
Messages
191
No mushroom cloud, but we haven't fired it up yet. Brian went over it very carefully (like only Brian can:)spin) and found it have been altered on a few separate occasions. One mod looked like someone tried to change it from a Super Bass into a Super Lead between sets, real hatchet job. So it's almost a SL, just the Rich mod to be done.
 

Marshallhead

New member
Joined
Jul 19, 2001
Messages
5,556
My half deathwall can give another push if the south wind from Canada invades our turf:lol


Sean-I find the sl circuit too bright BUT I seem to be able control it with adjustments and gasp----using my my tone knob on the guitar. Also,its seems once the useless bright cap is off the ch1 volume pot the lower volume tones become useful. RICH's tweaks dont seem to bright though-the man is a wizard.
 

BrianGWN

Great 'Double White' North ~ Electronics Specialis
Joined
Jul 15, 2001
Messages
1,401
>but then you never know what he has up his sleeve<
Yeah I did consider changing the power supply configuration to a "voltage doubler" arrangement so the existing 428 VDC output stage high voltage would be pumped up to over 800 VDC. That ought to make the amp really bark. ;) However I decided not to do that, I recalled the words of Scotty in an old original Star Trek episode: "Kuptain, the engines cannut take da strain!". :eek

>If there's a mushroom cloud over Canada in the morning, we'll know what happened.<
Geez give me a break, this is only a tube amp we are dealing with not nuclear armaments... Then again I do recall one of RICH's stories where some amp apparently died maybe had a serious failure of either the power or output tranni, and when the transformer let go as it overheated/self-destructed it produced some kind of "mushroom cloud of creeping death"...

>found it have been altered on a few separate occasions<
As I really got in there under the hood unfortunately it became apparent that previously there had been "too many cooks in the kitchen", looks like Rosemary had been playing the field as she showed signs of having been handled by a number of boyfriends, some with a rather rough touch. There was a fair assortment of kludge, I basically said to CanuckL if we want to get this amp into shape I better start at the front and go over the whole thing, trust nothing/no one.
It was obvious that some components had been cut off from the board accompanied with some kludgy attempts at wiring in other stuff, some sort of hanging right off the tube sockets. The previous conversion of V1 to split cathode was not so bad in comparison to some of the other messing around, but there was a fair bit in there that was of concern to me, things within a hair of shorting to something adjacent, some overheated solder connections that caused the wire insulation to melt and peel back created possibilities for a short, and traces coming loose from the PCB in a few places. I had to reinforce a few traces on the PCB with some bare wire if I was going to be confident it would all hold together. I had to undo and cleanup/redo some connections while adding some shrink wrap tubing to make sure it was safe.
Also some of the wiring to the tube sockets or input jacks started to break off, I'm wondering whether in some of the previous monkeying around someone really yanked on and strained those wires.

We got as far as fixing up the various fallout from the previous "abuse" of Rosemary, and adding most of the SB to SL adjustments. We drilled a couple of holes in the PCB for adding the 0.68 cap across the V2 820 cathode resistor, and yes RICH we did recycle the 0.68 that was originally part of the presence control ;). (I have a couple of extra small drill bits, 1/32 inch maybe even smaller, just for doing that sort of PCB electronics enhancements). ;)

...If we are going to do this we might as well do this right...
 
R

RICH

Guest
So....How does it feel to pull an all nighter on a marshall chassis? Life will never be the same, even the toaster won't be safe now. :lol2 :lolspin
 

Marshallhead

New member
Joined
Jul 19, 2001
Messages
5,556
RICH said:
So....How does it feel to pull an all nighter on a marshall chassis? Life will never be the same, even the toaster won't be safe now. :lol2 :lolspin


Or the fridge,dishwasher and stove:lol
 

Ed Rafalko

Les Paul Forum Member
Joined
Jul 15, 2001
Messages
6,287
When he starts remodelling his kitchen with a shotgun, it might be time to step back a bit.
But knowing Brian, he'll use a golf club instead.
 

BrianGWN

Great 'Double White' North ~ Electronics Specialis
Joined
Jul 15, 2001
Messages
1,401
>How does it feel to pull an all nighter on a marshall chassis?<
Hee hee, we were at it during the evening until partially into the night so it was not an all nighter. CanuckL decided he better kick me out some time around 2 or 3am, don't remember exactly when... ;)

>the toaster won't be safe now... Or the dishwasher<
The dishwasher? Why would I want to rewire any of the girlfriends?? :lol :doh
Then again I can think of a few women that would maybe benefit from having some kind of "master volume"... ;)
 

Sean

Goldie's Man in London
Joined
Jul 15, 2001
Messages
2,021
Speaking of MVs, what's the f*cker sound like?!!
 
Joined
Aug 5, 2001
Messages
191
Sean, it's not quite done yet, maybe over the weekend depending on Brian's schedule. I have to admit I do appreciate the amount of time and effort Brian has put into this project, the amp will be as good, no better than the day it left the factory. I can't wait to hear it either:dude
 

brianf

New member
Joined
Feb 20, 2002
Messages
3,164
Brian; Leave that poor amp alone. (Or is this the other one you told me about?). It sounded great. I'm going to hold the spare parts hostage until it's back together:lol2 :lolspin .



I'll call you when I pick them up. Good luck on your mods.

brianf
 
Last edited:

BrianGWN

Great 'Double White' North ~ Electronics Specialis
Joined
Jul 15, 2001
Messages
1,401
CanuckL, back at the Queen street wacky surplus store I came across a few assorted older CTS pots that had the correct top section for what we needed, 1/4 inch long threaded bushing. I'll swap those into a few of those non-bushing CTS dual audio pots so we should then be all set for the master volume control. We still need to locate an appropriate terminal strip to neatly securely mount the MV mod/wiring. I would like to get a five lug terminal strip with the middle third lug having the mounting leg. I saw a four lug strip today, close by not close enough...

brianf, the amp getting fixed up is NOT the one I bought at TGS. If you are there at the store on Saturday and they manage to locate whatever original parts were removed from the amp I bought, just make sure Brent and Larry know where they are, have them keep them somewhere at the store. I might drop by there late on Saturday or maybe sometime Monday to pick it up...
If you thought that Super Bass amp sounded great at the store, it will be even better once it gets tuned up, we have not yet heard it's full potential. You move up into another level of tonal possibilities once a classic tube Marshall has a good master volume added to it. :dude
 
R

RICH

Guest
""We still need to locate an appropriate terminal strip to neatly securely mount the MV mod/wiring. I would like to get a five lug terminal strip with the middle third lug having the mounting leg.""

Hmmm, thats exactly what I use for the master. I don't know if you have a radio shack up in that area, but they have them, a pack of 4 is under $2.
 
Last edited:
Top