Lee Jackson mod

Guitar Adjuster · Post by **Guitar Adjuster** » Mon Dec 18, 2006 4:27 pm

For those who want to build this, drop the 1000pf off the plate resistor, drop the 470K/470pf off the low input, add a .47 or .68 cap across the 820 ohm resistor on what is now V3A, drop the 1000pf bright cap, keep your filtering at 50/50 and use a 10H choke---I will guarantee this thing will rip your head off with either EL34's or 6550's. I use the 47k/470pf tone stack with mine and it kills. This is pretty close to the lee jackson mod......

Allen

awangotango · Post by **awangotango** » Mon Dec 18, 2006 8:07 pm

Thanks for the diagram. I will give this a shot and report back.

Tone Slinger · Post by **Tone Slinger** » Mon Dec 18, 2006 10:42 pm

Yeah that additional, or fourth gain stage was the "magic", so to speak, of what I was after back in the 80's, but nobody around here were doin those mods at that time.I hear alot of preamp gain on Pritchards rhythm, as well as lead. Sounds like 75 watt celestions as well. I tell you, the Splawn Quick Rod can get very close to Pritchards sound, here again basic 1959/800 design, with that fourth stage of gain.

awangotango · Post by **awangotango** » Mon Dec 18, 2006 11:54 pm

I hear the 75watters as well. Proof they can sound great if pushed into the cream-zone. Same with the 65's.

Devon8822 · Post by **Devon8822** » Tue Dec 19, 2006 9:03 am

Can someone explain to me about the whole gain stage thing? So they are different levels of gain? what gains tages does each marshall have stock?

rockstah · Post by **rockstah** » Tue Dec 19, 2006 1:52 pm

plexi - 3 stages of gain but you only use two at any given time with either your brightor normal channel.

2203 or marshall master volume amps take that extra stage and cascade it so what you give up in not having the normal channel anymore u gain in an extra gain stage for a 3 stage preamp.

the lee jackson mod adds yet another stage for a total of 4 stages of gain - (shred city.)

Mark

robert · Post by **robert** » Tue Dec 19, 2006 5:19 pm

Hi Devon,

why don't you build your own amp and test all the possibilities out? This way you'll learn by far the most, because it's practical, not empirical.

Regards

Robert

rockstah · Post by **rockstah** » Tue Dec 19, 2006 5:36 pm

robert wrote:Hi Devon,

why don't you build your own amp and test all the possibilities out? This way you'll learn by far the most, because it's practical, not empirical.

Regards

Robert

what i have done exactly.

robert · Post by **robert** » Tue Dec 19, 2006 7:46 pm

Yeah, and luckily you don't "hide" your practical experiences, but share them with the forum members. +1

Regards & happy soldering

Robert

MarkCameron · Post by **MarkCameron** » Tue Dec 19, 2006 10:31 pm

Most of Lee's mods where 3 gain stages. The added tube is for an added gain stage after the tone stack. He did do one with 4 gain stages but the one with 3 is the mod that most people had. Its a split cathode 1959 type(2 gain stages same values) circuit then from the treble wiper to a 220k w/a 220pf-470pf over it to the input of the added tube 100k/.022 to a 1meg master.Cathode for the added tube is .68/2.7k some I'v seen with 820ohm too. So Lee would only use 1/2 of v1 and 1/2 of the added tube.

awangotango · Post by **awangotango** » Wed Dec 20, 2006 12:30 am

This 3 stage mod would likely not add alot of distortion, but still crunch the preamp ? I would say that is the mod I'd be interested in. 4 gain stages is likely too much distortion for the tones mentioned above (Dave prichard) since i;m getting plenty with 3 stages. i just need that extra crunch. Can anyone translate this 3 stage mod to a diagram.

Tone Slinger · Post by **Tone Slinger** » Wed Dec 20, 2006 11:21 am

Does anyone know what model Marshall Lee is performing the mod on in his video ? I would hope it is on a PTP as opposed to a PCB. At this point, for me, it would be easier to follow on a PTP.

Guitar Adjuster · Post by **Guitar Adjuster** » Wed Dec 20, 2006 11:26 am

The DVD shows him modding an 80's JCM800 PCB Marshall.

Devon8822 · Post by **Devon8822** » Wed Dec 20, 2006 3:35 pm

Can you get higher gain stages with pedals? like for example a ts 808 and a plexi?
Could you get a 2 stage to 3 stages with a pedal? or a 3 stage to a 4? is that how it works or am I confused?

rockstah · Post by **rockstah** » Wed Dec 20, 2006 4:38 pm

Devon8822 wrote:Can you get higher gain stages with pedals? like for example a ts 808 and a plexi?
Could you get a 2 stage to 3 stages with a pedal? or a 3 stage to a 4? is that how it works or am I confused?

take a look at a plexi layout .
think of a gain stage as half a tube a cap and 4 or 5 resistors = gain stage.,( in any given 12ax7 we have two tubes in one)

from left to right we see the first tube = 2 gain stages. one for normal channel one for bright channel.
the next tube is gain stage( tone circuit ) and a cathode follower.
the next tube is the phase inverter.