MkIII owners, read this

[JOEY B.]

I recently bought a MkIII long head and noticed a spot for a switch on the rear, to the right of the heat sink. I then bought a DPDT switch and wired it to the outer power tube sockets to make a Pentode/Triode switch. I have seen a short head with this switch mounted underneath the chassis, between the power tube sockets, as well. I believe it as much of a "required" mod as the R2 Volume mod, from what I heard tonight. All this is just my opinion, for sure.

 

[GIG4FUN]

What does it sound like? give it up man! (like a green stripe?)

I think Andy does this mod, I hope he chimes in!

 

[Monsta-Tone]

The Pentode/Triode switch is a 1/2 power switch.
It really works, unlike the 60/100 watt switch that just take the headroom of the amp away.
:lol: Maybe Mesa doesn't use them because they can't patent it! :lol:

I basically add this to every amp I own. With 3 small kids, I can't really unleash my DC-10 or Heartbreaker very often!

 

[silentrage]

Joey, sorry to sound like a noob but what exactly does the switch do and why do you think it's so necessary?
And... care to do a little how-to guide for us technically inept forumites?

I'm getting a blue stripe in a few days, I gotta get ready for all the modding action, lol.

 

[GIG4FUN]

Joey, what exactly does the switch do and why do you think it's so necessary?
And... care to do a little how-to guide for us technically inept forumites?

+1
That's really what I should have said!

 

[Monsta-Tone]

It's really not that difficult, but you have to make sure that it's done right or the magic blue smoke will escape your amp and it's really hard to put back in!

Basically, if you screw up, bad things happen.


http://www.tone-lizard.com/Marshall_Myths.htm
There is a drawing toward the middle of the page.

 

[GIG4FUN]

Basically, if you screw up, bad things happen.

words to live by :lol:

 

[GIG4FUN]

It's really not that difficult, but you have to make sure that it's done right or the magic blue smoke will escape your amp and it's really hard to put back in!

Basically, if you screw up, bad things happen.


http://www.tone-lizard.com/Marshall_Myths.htm
There is a drawing toward the middle of the page.

Thank you for the link ! (I just saw that part of your post...// "tired today" \\ )

 

[Monsta-Tone]

Not a problem.
If it's not a trade secret, I don't mind helping at all!

There are lots of mods that I can't give out though.


All I can say is do your homework when it comes to safety and actually doing the mod.
make sure the caps are drained and the amp is unplugged.
Make sure the drawing and the end result are the same.

 

[silentrage]

How does this mod work with the simulpower switch?
And...is the r2 gain mod "trade secret"?

 

[Monsta-Tone]

I've never tried it with a Simul amp.

As for R2, there is a thread with some really great pictures floating around here somewhere. Basically, you just replace a resistor (132 I think, don't have the drawings in front of me). It's a 15k resistor that gets replaced with a 25k linear pot.

I got this directly from Mike B. at Mesa. Some guys say to use a 250k pot, but I've had some bad luck with a value that high. The 25k seems to be just about right.


I think the original thread is somewhere in the Vintage Amps section, but may be in the Mark Series section.

:mrgreen: Just keep in mind though that if you mess it up and then send it to me, I drink Corona, and there is a case of beer charge plus the standard charges! :mrgreen:

 

[Monsta-Tone]

Found it!

http://forum.grailtone.com/viewtopic.php?f=3&t=18520


:lol: Don't forget the case of beer if you screw it up! :lol:

 

[silentrage]

Thanks for digging it up man. I need to do that too, but I was actually asking about the r2 Gain mod. =)
Corona light is my brew too!

 

[Monsta-Tone]

I've been working on one, but like I said, I gotta feed the kids too.
Try getting any drawings out of some other guys.

I should probably switch to light beer. The spare tire is growing! :lol:

 

[JOEY B.]

As far as I'm concerned, Triode sweetens Channel 1, Pentode gives Rhy2 a needed punch, and the Lead channel is a toss up. I also warmed up the bias to about 50% MPD for all the power tubes. Here is a pic of the business end of "Mean Green" and a nice shot of my door greeter.

 

[silentrage]

How did you adjust the bias? A bias mod?

 

[JOEY B.]

How did you adjust the bias? A bias mod?

You can add a bias pot or a fixed resistor into R117 at the lower left corner of the preamp board (viewed from the rear of the chassis). This is somewhat dangerous if you do nat drain the caps. You also need a way to measure the current draw of the power tubes.

 

[Monsta-Tone]

I always do a bias pot when I can. It just doesn't make any sense to change out a resistor and then have to do it again later on.

This is somewhat dangerous if you do nat drain the caps.

:shock: :shock: :shock: I forgot once! Only once, that's all it takes! It will kill you or keep your ass in line!

 

[Facelift]

how do you drain the caps?

 

[GIG4FUN]

how do you drain the caps?

I connect the capacitor to jumper cables and then to my clothes dryer and dry clothes until it's drained. :lol:

:shock: careful guys...we're gunna lose someone here :?
Just send your stuff off to Andy (Monsta-Tone) and live long and prosper.