Mod kits

martyred · Post by **martyred** » Fri Feb 25, 2005 10:24 pm

Anyone know of a good place for mod kits, or schematics? Ive been searching around pretty much to no avail. Ive found certain things such as an added FX loop, but triode/pentode switches I can only find from Torres and Ive only heard bad things about them. Could always find a schem and buy the parts to go along with it, just having trouble finding one

Flames1950 · Post by **Flames1950** » Sat Feb 26, 2005 2:24 am

For a half power triode/pentode type of thing you might check out the schematics for the Jubilee amps. Here's the schematicheaven.com url for Marshalls so you can download them:

http://web.archive.org/web/200312021543 ... heaven.htm

A lot of these types of ideas you can get straight off one of Marshall's own schematics this way. I had drawn up a post-phase inverter MV that I was thinking of converting my 2204 to, based on Marshall's version of the Park "Rock Head" amp of the late 70's. Those who think the so-called "Rich Mod" master is a newer idea should take a look, Marshall knew how to do it long before that mod rolled around!

Flames1950 · Post by **Flames1950** » Sat Feb 26, 2005 2:26 am

At any rate, I too have heard many a bad thing about Torres' kits and would avoid them, but that is an opinion based on other people's experiences not my own........

Necrovore · Post by **Necrovore** » Sat Feb 26, 2005 1:42 pm

As far as Torres goes I have never tried one of his amp mods. Heard nothing but bad things about SOME of them and SOME of the way he does stuff. BUt have never been told exactly why though. You always get the "Oh I don't like the way he does xxxxx". He is still in business so obviousely he is doing something right.

I have tried several of his guitar mods and have really liked them. My personal favorite is his Mid mod for guitar.

Flames, as for the Jubilee schematic over at Larry's site. I have picked up like 6 different schematics off the net for the Jubilees. The are all fairly poor quality. The clearest Jubilee(2550/2555) schematics are in the Doyle book. even then you have to use a magnifying glass and jump between the two schematics on pages 224-225 to figure out all the values and some are clear on one but unreadable on the other. Good ideas though on the half power mod.

Billy Batz · Post by **Billy Batz** » Sat Feb 26, 2005 4:45 pm

Nec I have a 2555 schem that isnt messed up. Its not the best quality but I can make out every value. I may have to zoom in for one or two. Ill send it to you but Im almost posative I got it from Larrys SchHeavn.

Necrovore · Post by **Necrovore** » Sat Feb 26, 2005 6:50 pm

Yeah Please if you can. the copy that I got off his site a while back looked like a really bad xerox copy then made into a .pdf. the lines and values were oversaturated i guess you call it so a lot of it got garbled out.

Flames1950 · Post by **Flames1950** » Sat Feb 26, 2005 11:42 pm

Flames, as for the Jubilee schematic over at Larry's site. I have picked up like 6 different schematics off the net for the Jubilees. The are all fairly poor quality. The clearest Jubilee(2550/2555) schematics are in the Doyle book. even then you have to use a magnifying glass and jump between the two schematics on pages 224-225 to figure out all the values and some are clear on one but unreadable on the other. Good ideas though on the half power mod.

Yeah, I just made sure they were present and accounted for, I didn't actually download them to see what they looked like. I haven't looked too closely in the schems for the Jubilees in my HOM either. But if you can find a clear schem the Marshall high/low power switching would be my first stop.

Flames1950 · Post by **Flames1950** » Sat Feb 26, 2005 11:45 pm

I did notice that the 50watt Jubilee schematic in the GT book is pretty clear. The same high/low power switching scheme also looks like it appears in the JCM900 schematics, most of which are pretty clean from what I've seen.

martyred · Post by **martyred** » Sun Feb 27, 2005 3:52 am

Just finished reading a lot, especially about tubes in its history and application, from Wikipedia and Google. Eyes hurt a bit, do wish theyd have a monitor as soft as paper

Started by staring at the schematics. Ill be the first to admit I can only translate loosely, sort of like latin.

So my first question is, how does a simple modification change how the tubes operate, from pentode to triode? Is it as simple as that 1k 5w resistor, and the flip of a switch? And how would it translate specifically to my plexi?

Flames1950 · Post by **Flames1950** » Sun Feb 27, 2005 8:05 am

Hell, I'm not sure I totally understand the concept either, although it's not truly switching from pentode to triode even though that's what many amp manufacturers call it. The screen resistor shouldn't get switched out; the difference is where the voltage to that screen is coming from. On the Jube's it's switching from getting the voltage from the output tranny primary, or getting a somewhat lower (and better regulated?) voltage after the choke. On the 900's (and the rackmount power amps of that time period) it's switching from voltage at the output tranny primary to voltage taken after a 100ohm resistor, which takes the place of the choke. It's the difference in the screen voltage that will change how the tube operates, from the way it looks.
All of which is semi-educated guessing; if George spots this thread maybe he understands and can explain it far better than I.

myker · Post by **myker** » Sun Feb 27, 2005 11:23 am

george actually told me how to do this mod before, you use a dpdt switch and connect the screens to the grids of your power tubes. turing them into triodes. george warned me that i probably wouldn't like it all that much and i didn't. the volume change is hardly noticable and the lows get a bit mushier.
i might have georges e-mail where he told me how to do it, lemme check..
mike