Lead 100 Watt started

[xtian]

With a lot of respect for what are iconic amps, what was the reason for running the jumpers above board and not below as in the Dumble amps? Same question regarding the additional holes to allow the lead wires to exit under the board. Were these esthetic decisions or do you find that one technique verses the other makes for a cleaner, noise free amp?

An aesthetic choice, I think.

[pompeiisneaks]

Agreed. there may be rare occasions where you could cross some signal path with b+ and 'maybe' inject noise but I think that's extremely unlikely. More than anything I think it's just for looks... if underneath they're 'out of sight out of mind' but on top they're more accessible and 'visible' to a future repair person etc.

~Phil

[angelodp]

Turret board question. No good deed.....

The Turret board from Mojo was not a good fit to the stand-offs and I had to modify the hole sizes to make the fit...ergh!! No Biggy.

But as I look at what they show online and what I have here, split turrets? I wonder if I am going to have issues with these style turrets. They have less mass and will dissipate heat more rapidly. They are not what I am used to. What say yea? At this stage Mojo is swapping the power caps to spec, I got 6-33/33 instead of 6-50/50's, so thats good. I may just pop for the board they show with proper turrets. Maybe this Covid thing has folks short-handed.

[angelodp]

Ok Mojo is sending caps and new board.... all good.

I have these two caps to add to the circuit. The big bad snubbers. Look Good?

[angelodp]

I am asking if these older sealed caps will withstand this circuit. they are molded types and show no leakage and measure accurately for the uf. My understanding is that the molded caps have a longer life than other the wax caps.

[martin manning]

Why take the chance? I wouldn't use those or any other caps in that location. Did you test them at high voltage, BTW?

[angelodp]

Ok so I gather that you don't see that those caps are necessary in this circuit. No I did not test them at high voltage, not sure how to do that.

[angelodp]

I am a little wary of the schematic from Mojo as I found an error, albeit a minor omission of a connecting dot. The bias circuit also varies slightly from what I see in the traditional Marshall schematic. I am preparing a layout that will merge the variations in the mojo method but adheres to their schematic. Schematic matching the layout. Does this schematic look viable/correct? The build has a fender style bias pot between the power tubes with wires running out to the board. My thought is to place the 47k directly on the pot.

My concern, aside from some differences in values, is the arrangement of the bias circuit. If I follow the Mojo method will that be trouble.

[Alnico]

Most people building Marshall clones use a trim pot on the turret board. See step 14 here:

http://www.valvestorm.com/sites/default ... T_V2.1.pdf

[angelodp]

Hi, yes I have that guide and seen that thanks. I am trying to stick with the kit layout and my question relates to whether the two bias circuits are functionally equivalent.

[angelodp]

The Mojo schematic has the neutral side to fuse not the hot. I should reverse that. Is there any reason to put the fuse on the neutral side? I think not,

[pompeiisneaks]

Never, it means if it blows, that the hot side could still be hitting the chassis somewhere and is very dangerous. The hot side should be fused always.

~Phil

[Snicksound]

Yup I told him all that and he insisted and bought the amp. Kids.

Meh, in my experience, when 100W is too loud, 30W is also too loud anyway. At that point, it's more about weight and cost (acquisition and retubing).

After building a bunch of 15-25W Marshall type circuits, I've started going back into big bottles at 50W+. There's just something about that big cab (still just a 2x12 though, but a vertical one with Creamback M65s) pushing me in the back.

Power is more about headroom, You can get loud with 10W, but 100W has that extra push in the lows.

[angelodp]

Correction 5.6k shared.

I see that on some vintage builds the 5.6k grid resistors are shared by two tubes as opposed to using a single resistor at each Power Tube grid. Are both methods equal in operation?

[angelodp]

Moving along, slow and steady. Appreciate all the input and assistance.