JTM 45/100 - Build story

[neikeel]

yes, i like it too, although it's red, but not a problem to me, that's ok. and it handles the power i need.

i noticed something on George's amp : on the output jacks there's

'one wire going to the ground,
-one wire going to the output of the impedance selector,
-one wire from the OT i guess,
and an extra wire ( compared to the layout i uploaded ) , a black wire. i really have no idea of what this is.

plus, under the jacks, there's this blue wire ... and a pink wire at the same point.
normaly it should be a black wire from the OT at this point. so ... mystery ...

One black wire is the centre tap of OT primary, the blue wire is from OT to pin 3 of V5, the orange wire to pin 3 of V6.

[Xplorer]

yes but there's a fourth black wire, also coming from the OT direction, and also going to the ground. i don't know what that is.
i thought i was supposed to have only 3 wires connected to the output jacks.

looking at the picture again, where the blue wire from the OT goes, pin3 of V5, i think that the pink wire soldered toi the same point is going to pin3 of V4. just another kind of way to set the wires i guess.

Where did you guys ground the power cap board ?

[neikeel]

yes but there's a fourth black wire, also coming from the OT direction, and also going to the ground. i don't know what that is.
i thought i was supposed to have only 3 wires connected to the output jacks.

looking at the picture again, where the blue wire from the OT goes, pin3 of V5, i think that the pink wire soldered toi the same point is going to pin3 of V4. just another kind of way to set the wires i guess.

Where did you guys ground the power cap board ?

I think that is an extra ground?

That amp has been playeds around with a bit and not the ideal reference for a build - although your amp is coming along nicely!

[Xplorer]

Thanks Neil !

[Xplorer]

progressing

[neikeel]

Good, but just double check the quality of those joints between the jacks and the OT - look a bit blobby - did the solder flow properly?

[Xplorer]

yes, on the jacks ? on the left ? that's because there's some thick wire under it ( black and orange wires ) , cause i thought i'd give more contact there ... so more tin too. do you think i should re do this ?

[Xplorer]

Lacing cord on all this.
i hope that joining closely together all these wires isn't gonna bring noise ! i wonder why i twisted the heaters wires if i'm lacing some AC wires super close to it ! how bad is it ? should i worry or is it just fine ?

[BoogieEngineer]

Looks great. Be sure you scrape the output wires like the instruction says. Also I'd try putting the boards in their places to make sure everything fits

[neikeel]

Looks great. Be sure you scrape the output wires like the instruction says.

Methinks you are referring to the self lead Dagnall clone C1998 OT which has varnish coating on the secondaries? The Drake repros are normal stranded wire and only need tinning before soldering.

Also I'd try putting the boards in their places to make sure everything fits

Always a good idea. I build the board up completely with wires a little longer than needed and 'dress/trim' them later.

[Xplorer]

Be sure you scrape the output wires like the instruction says. Also I'd try putting the boards in their places to make sure everything fits

I'll have to look at the definition of "scraping" ^^ in the dictionnary. Are talking about the 100w kit instructions ?
the output wires would be the wires arriving to the output jacks , like Neil advised me ?

Yes, as soon as i'll have my paxolin sheets cut, i'll see how they go inside. i'll have to ,prepare the input jacks and a ground point on the chassis prior to the boards.

Always a good idea. I build the board up completely with wires a little longer than needed and 'dress/trim' them later.

yes, i'll do it this way, although some wires will already be in place, cause i wouldn't like to have some hard time trying to solder a wire on a delicate spot, and hard to access ...

Please guys, do you know where the power cap board should be grounded ? i can't see it on pictures

[BoogieEngineer]

Be sure you scrape the output wires like the instruction says. Also I'd try putting the boards in their places to make sure everything fits

I'll have to look at the definition of "scraping" ^^ in the dictionnary. Are talking about the 100w kit instructions ?
the output wires would be the wires arriving to the output jacks , like Neil advised me ?

Yes, the 4, 8 and 16 ohm wires. Simply use a utility knife and scratch the stranded core thoroughly. Otherwise the wires might not be able to conduct because of the coating and you would fry the OT.

[Xplorer]

i didn't know that, it didn't seem to have a coating ( ?? ) i already soldered the wires of the OT, should i unsolder it ?? are you sure ? i'll ask to Brian Wallace i'm a bit surprised.
Then , should i scrape every wires ? the stranded wires from the PT too ?

please, does anybody knows where's the power cap board ground, on an original 45/100 ?

[neikeel]

I am pretty sure that on an original it is like my EL34 amp a short link from the PI cap turret to the back of presence pot bus rail.
Not sure that this is th ebest palce for it. IIRC I had one of these in last year (well a PA) and it had a ground loop that I lost when I moved the cap board earth to a central point on one of the PT bolts.

[Xplorer]

oooh yes, a bolt of the PT , that should be fine !

so in some cases, the back of the presence pot is used to ground the pots on the cap board's ground, and in your case it was to ground the cap board itself on the pots ground coming from a bolt near the input jacks i guess ?

ok, i'll look for the first PT bolt near the cap board, thanks !