MIII: blue -> green?

[boogiemon]

Anyone know what's involved in changing from triode to pentode for the two outside sockets? Not interested in being able to switch between the two, just wondering if i could manage the mod myself.

thnx,

 

[>Photi G<]

It shouldn't be too hard, the main thing is that you will have to supply a Screen Grid supply to the Class A pair, and disconnect the plates from the screens, and possibly swap/eliminate a few other components and connections. A simple mod for someone who knows what they're doing.

 

[okgb]

Google it but , basically
conecting the screen grid to the plate
[ instead of supply voltage trough a resister
and make that switchable.
it's easier than i describe

 

[boogiemon]

Google it but , basically
conecting the screen grid to the plate
[ instead of supply voltage trough a resister
and make that switchable.
it's easier than i describe

that's hopeful but while i'm good w/a soldering iron, i know next to nothing about electronics. i did google it & didn't get much that i could use: not looking to be able to switch back & forth just thinking about a permanent pentode config.

 

[okgb]

the switch lifts the screen from a wire [ voltage ]
to a resister to the plate , sometimes the resister is omited
but better with it
switch , two wires , one [ 1k ? ] resister
not the best version but something to get you started
http://www.tone-lizard.com/Marshall_Myths.htm

but there's got to be boogies schematics you can copy
my simul class is basically that

 

[boogiemon]

Against my better judgement i made the mod & everything seems to have worked out ok. i like the increased headroom & don't miss the softer feel it had. Assuming i did it correctly, the mod is pretty simple: i just ran the resistors on the outside sockets from pin 4 away from pin 3 and over to the same place where pin 4 goes for the two inside tubes. That was it: no smoke = success.

 

[ltd2recto]

I thought the III+ mod was changing c30 & c516. Is there more to it than that?

 

[boogiemon]

Dunno, MB did everything but the pentode mod.

He was actually *extremely* cool about the whole deal. When i got the MIII i took it up to the factory to have it tuned-up/checked out & to have the + mod done @ the same time.
When i picked it up, MB told me to let him know if i had any questions or issues. After playing it @ home it still seemed *really* bright as compared to my no-stripe so i called him & he said "np, bring it back up & i'll make a couple quick changes". A week or so later i took it up & that's when he changed the C30 and presence caps.

How righteous is that? i'm a nobody in the music world & one of the main guys at Mesa went outta his way to tweak a 25 year old amp for me. i wouldn't believe it if i hadn't been there. 8)

I thought the III+ mod was changing c30 & c516. Is there more to it than that?