JTM 45/100 - Build story

[Xplorer]

ok, so no mistake here, i'll do it your way, using the extra turret near the diode, to connect the ot wire, the whoke wire, and the wire from the power board.

i'll post some other stuffs to make things clear before i enter the mess of wires to connect. it'll make my life easier ^^. And hopefully, it'll help the futur JTM builders if i detail everything.

[Xplorer]

Here is the last update.

i think about connecting the ground of the output jacks on V6 solder lug ( the one with the 1 ohm 2w resistor ) .
about the pots , input jacks, and filter board ... i can't see, from the pictures, where to ground each points ...
any advices ?

Edit : pictures erased for the update

[Dom]

Billy's layouts are a very good help, but not 100% authentic in regard to the original layout.
One spot is the turret next to the diode, where CT of OT primaries, red wire from mains caps, and choke is connected to (as discussed in the last posts).
And the first dropping resistor (8.2K) is also upside down. It should be 180° turned around with all its connecting wires.
See the red HT wires:
http://www.amparchives.com/album/Marsha ... 00255.html" onclick="window.open(this.href);return false;

That does mean you have to swap the red wires of the PI and screens filter caps.
one choke wire and thr wire going to pin 6 of V4 is connected next to the turret of the 15K R in the bias section.

[Xplorer]

Hey Dom, thanks for pointing this ! indeed, this afternoon i had troubles to understand the difference between the picture from George and the layout. Is it all ? looking at all the red wires under the filter board, i remember that i couldn't see them the same way on the layout.

So, i should have the choke wire going on the tube sockets side ( opposite to the pots side ) .
for the two wires coming from the power caps board, ok, i just need to invert them.
But for the wire from the 8k2, going to the 100k and 82k, i'm not sure yet, as well as the one going to the tube socket.
i need time to see it clearly.
what is PI, and thr ?

[Dom]

Yes, choke wires go to the tube side turret row.
PI = phase inverter (V3)

I've made a quick and dirty layout of this section, don't look at the colors, I can't get them right when saving as PDF file.

[neikeel]

You can wire it the Billy Batz way - it will still work. Marshall went to that way in the early 70's I think for ease of assembly reasons (ie dropping a completed board in with minimal under board soldering.

I usually build my amps with the bus wires crossed and the screens/choke/screens cap feed north (ie near the sockets) and the PI cap south (nearest pots). As long as you get the bus wire correct for the hook up method you chose it does not really matter.

[Xplorer]

Super cool ! i appreciate. I'll update "my" layout with it. the only thing i'm not sure to understand is this double purple wire from the 27k.
Neil, what buss wire did you mention please ?
i know there's a buss wire going on all pots ground, which then is grounded .... i don't know where but i don't see which other buss wire there would be.

[Xplorer]

Here is an update.

i didn't find yet some pictures where it shows how the input jacks and the grounds of the filter board from the 100k/820 ohms and 250uf/820ohms go.

for the others, i draw the buss wire of the pots ( but i didn't see where it's getting grounded yet ) , where the 10uf caps and the 32uf cap of the filter board get connected.

for the light indicator ( which is supposed to handle 240v ) , i think i've made a mistake by saying it should get soldered on the two pins of the AC switch. Shouldn't that be in serie with the wire coming out of the AC switch or something ?

Edit : picture erased for update

[Dom]

The purple NFB wire was usually connected to the 16Ohms tap.
Sometimes speaker grnd was connected to the negative of PI filter cap. I only know this from pics and dunno how correct this is, or if it was changed when servicing the amp.
http://amparchives.com/album/Marshall/1 ... _5344.html" onclick="window.open(this.href);return false;

[Xplorer]

oh, i see.
But what if the amp is set on 8 ohms or 4 ohms for whatever reason ? this point isn't grounded anymore ? what would be the result ?

Should i keep the speakers chassis ground to V6 lug ?

[Xplorer]

Meanwhile, some small progress pictures.

bulgin plug grounded to the side on the chassis, through a mounting screw and a lug.

the "C" wire from the transformer goes to the fuse, and then to the ground thanks to a solder lug connected to the chassis and to the end of the fuse. so : the bulgin plug ha its own ground, as well as the heaters wire, and the "C" wire.

And some connections + one 100k resistor on the preamp tube sockets.

[neikeel]

I would keep the speaker ground lug short down to the nearest socket ground hole, if you are using the traditional 2 output arragement you could run a wire from the bus wire lug on the second jack down to the V4 earth or the first one as shown in your pic to V5 socket earth.

The bus wire I was referring to earlier is the under board bus wire (albeit covered in insulation, although you may be using normal wire?).

I use 27k NFB hooked to the 16ohm tap on the selector. It will remain that amount of NFB regardless of where your selector is as it is hooked directly to the OT windin by that wire.

Someone else posted whilst composing so lets see

[Xplorer]

oh ! yes i didn't realise it would be connected to the winding of the OT anyway ! thanks !

Do you know about the three remaining ground points ? and the light indicator, to make a correct build ?

[Xplorer]

oh, it seems that the input jacks are grounded simply on the chassis with a screw and a solder lug. And both pair of jacks have a black wire ( ? )

The grounds of the 250uf/820 ohms goes at the same point, as well as another grounded point ... but it disapears under the board. maybe the ground of the 100k/820 ohms point ? but i see a pink wire coming from this point, going to the pots ..
What do you think ?

[Xplorer]

i found my mistakes :

indeed, under the 100k/820 ohm point, a black wire goes to the solder lug of the chassis where the input jacks and the 250uf/820 ohm points get grounded.
the only thing i don't see is what is this brown wire coming also to this point ...