Lead 100 Watt started

[xtian]

Isn't it fun to work in such a huge chassis? Compared to, say, a Tweed Deluxe 5e3...

[angelodp]

Yes indeed, its like a swimming pool. Getting there.

A

[pompeiisneaks]

Yeah I've just ordered my chassis for the dumble modded bassman and I went as big as I could... my arthritic hands don't do well in those tiny chassis anymore

~Phil

[angelodp]

So here's a quick question. The Mojo layout has the HT fuse perilously close to the 5W 1K. I had to bend the leads a bit and pull the cement resistor away for the fuse. I think I have just enough room to make the connections. The 5W is safe below with no undue shorts. I am wondering if I should take another tack. The 5.1k grid R is jammed just below but its ok I think. Ideas?
Ange

Quick fix - I bent the tabs back 90 degrees and it should be fine. Bit of shrink tube after soldering.

[xtian]

Quick fix - I bent the tabs back 90 degrees and it should be fine. Bit of shrink tube after soldering.

Perfect.

[angelodp]

Hybrid layout. Here is the hybrid layout I am using along with the Metro standard 100W Super Lead 1959 schematic. This layout includes the PPIMV addition as well as the 68K's moved to the V1 socket. I have included the Mojo Transformer colors which match the MM colors noted in the Metro doc. I am building per the Metro build guide and wanted to have a layout that combined the Metro layout with the additions I am using.

Would appreciate any seasoned eyes to have a look and see if I have any errors you can spot. I would love to have this checked out before I finish out the build. Its easier than dealing with build errors.

Best A

[angelodp]

Hi, have been reading a lot of threads where there are numerous issues with the Mojo kits. Pity as they are a supplier with a range of items. I am building a kit (purchased by a young guy....Colossal yes you warned me....no he did not listen), and there have been issues. I am relying on the Metro guide.

I have these 47k's for the 50/50 caps. They are meant to be 2w - do these look like 2w?

[Phil_S]

I'm no expert. I'd say they are 3W or 5W. More likely 3W. Certainly, at least 2W.

Look at this data sheet. On page 2, there is a size chart that might correspond to what you have.
https://www.mouser.com/datasheet/2/315/ ... 150021.pdf

[angelodp]

Thanks Phil. Good to go. Although the original schematic calls for 56k. You reckon the 46k will be fine- erghhh!!Mojo.

[sluckey]

There will be 250V across that 47K resistor so the actual power dissipated will be 1.33 watts. A 2W resistor will get very hot. I'd feel better with a 3W resistor. The 56K resistor would dissipate 1.1W. I'd feel OK with a 56K/2W but would feel much better with a 56K/3W. Cost is $0.50, so $1.00 would buy a lot of reliability and piece of mind.

Keep in mind... If you use a 47K on that cap can you must also use a 47K on the other cap can in that stack. These two equal value resistors force the B+ voltage to split equally across each cap can.

Oh, and one more thing... You are looking at one of the differences between the mojo kit and the metro kit. Metro used two 56K resistors to force the B+ to divide equally across the cap cans. Mojo used no such resistors so they would not have been included in their kit. Instead, they connected the PT center tap to the cap cans to force an equal split. Look at the mojo schematic. I believe this was recently discussed in another of your threads. This is an example of one of the pitfalls you will come across by using metro instructions to assemble a mojo kit. There will be more. Be careful.

[angelodp]

There will be 250V across that 47K resistor so the actual power dissipated will be 1.33 watts. A 2W resistor will get very hot. I'd feel better with a 3W resistor. The 56K resistor would dissipate 1.1W. I'd feel OK with a 56K/2W but would feel much better with a 56K/3W. Cost is $0.50, so $1.00 would buy a lot of reliability and piece of mind.

Keep in mind... If you use a 47K on that cap can you must also use a 47K on the other cap can in that stack. These two equal value resistors force the B+ voltage to split equally across each cap can.

Oh, and one more thing... You are looking at one of the differences between the mojo kit and the metro kit. Metro used two 56K resistors to force the B+ to divide equally across the cap cans. Mojo used no such resistors so they would not have been included in their kit. Instead, they connected the PT center tap to the cap cans to force an equal split. Look at the mojo schematic. I believe this was recently discussed in another of your threads. This is an example of one of the pitfalls you will come across by using metro instructions to assemble a mojo kit. There will be more. Be careful.

Steve, the kit has two 47k resistors and the Metro guide does connect the PT center tap with red/yellow wire.
As I look at the two schematics, Mojo and 1959 Marshall, it looks very similar. I have simply changed the color code on my layout in the 100w lead thread from yellow/red to yellow.

[angelodp]

There is a question on the power supply as I compare the Mojo layout to the Metro. I have reconfigured my build to reflect the Metro build but the Mojo seems very similar except for the 46k instead of the 56k. Both do use the CT of the PT to split the 50/50caps... NO?

[sluckey]

Please excuse my previous post. I was looking at the wrong cap stack. Everything I said in that third paragraph is wrong. Sorry for the confusion.

[angelodp]

Steve, no worries, I am trying my best to not screw this up so any help is greatly appreciated. If you have a sec to look at the proposed layout I cobbled together on the 100w thread. I think my transposition of the mojo to Metro is good, but your experiences eyes are always welcome and appreciated.

A

[sluckey]

That's correct. Sorry for my confusion in the other thread.