Tweed Deluxe 5E3 Output Transformer Question

[Fingolfen]

Okay - so... say Steggi wanted to be "fancy" and use an Mercury Magnetics transformer for the 5E3 build... Looking at the wiring diagram:



The red, blue, brown, yellow, and black are all pretty clear...

But the MM transformer has different wire colors... and only has four coming through the bottom of the chassis... here's what I'm gleaning from the spec sheet:



Question is what would one do to make the black connections to the MM output transformer? Would you run a separate wire and solder it to the self lead on the OT?

 

[owlexifry]

Okay - so... say Steggi wanted to be "fancy" and use an Mercury Magnetics transformer for the 5E3 build... Looking at the wiring diagram:

View attachment 71078

The red, blue, brown, yellow, and black are all pretty clear...

But the MM transformer has different wire colors... and only has four coming through the bottom of the chassis... here's what I'm gleaning from the spec sheet:

View attachment 71079

Question is what would one do to make the black connections to the MM output transformer? Would you run a separate wire and solder it to the self lead on the OT?

ive never seen a direction or suggestion like this before.
seems fucken dumb to me.

so it's clear the 'self-lead' is the COM/ground lead for the OT secondary.

many like to just ground this to the chassis per the output jack sleeve (output jack grounded to chassis w/ star washer) - as is indicated on the mojo diagram.

as the mercury diagram suggests, soldering this lead to the output transformer frame does the same thing (but it's still stupid, often OT transformers are covered in varnish)
if i was gonna do something like that, it would make more sense to just use a solder tag washer and screw it down with the OT mounting bolt like a normal person.

having said that, since studying ground scheme references (https://www.valvewizard.co.uk/Grounding.pdf) it appears a better practice is to return this ground lead from the output jack (output jack isolated from chassis) to the filter cap (-) node/star of the power amp (the first 16uF filter cap).

(if this was an amp that had negative feedback - the ground lead would ideally return to the stage (filter node) that the negative feedback also returns to - ie. the phase inverter stage / filter cap node)

(pg. 12)




ground scheme layouts are contentious, everyone has an opinion, and i'm not telling you what to do.

IMO - grounding it to the output jack per the mojo diagram should be adequate for this circuit.

the 'better' practices I've shared above can be difficult to employ, especially if you want it to look pretty.

honestly, i don't see the point in going with a different, more expensive OT when the one that comes with the mojo kit will be perfectly adequate.
diminishing returns and all that.

 

[Giorfida]

ive never seen a direction or suggestion like this before.
seems fucken dumb to me.

so it's clear the 'self-lead' is the COM/ground lead for the OT secondary.

many like to just ground this to the chassis per the output jack sleeve (output jack grounded to chassis w/ star washer) - as is indicated on the mojo diagram.

as the mercury diagram suggests, soldering this lead to the output transformer frame does the same thing (but it's still stupid, often OT transformers are covered in varnish)
if i was gonna do something like that, it would make more sense to just use a solder tag washer and screw it down with the OT mounting bolt like a normal person.

having said that, since studying ground scheme references (https://www.valvewizard.co.uk/Grounding.pdf) it appears a better practice is to return this ground lead from the output jack (output jack isolated from chassis) to the filter cap (-) node/star of the power amp (the first 16uF filter cap).

(if this was an amp that had negative feedback - the ground lead would ideally return to the stage (filter node) that the negative feedback also returns to - ie. the phase inverter stage / filter cap node)

(pg. 12)
View attachment 71082

View attachment 71081

ground scheme layouts are contentious, everyone has an opinion, and i'm not telling you what to do.

IMO - grounding it to the output jack per the mojo diagram should be adequate for this circuit.

the 'better' practices I've shared above can be difficult to employ, especially if you want it to look pretty.

honestly, i don't see the point in going with a different, more expensive OT when the one that comes with the mojo kit will be perfectly adequate.
diminishing returns and all that.

I’m a big proponent of saying that the output transformer in amps that are pushed hard is one of the biggest factors in tone. That said, I’ve had good luck with Heyboer transformers in the past… and looking at their site they cite Mojo as the place to buy them… yet on mojo’s site, they only show Moko transformers. So I guess we know who makes them for Mojo!

That said, any heyboer or mercury will be a decent improvement over the New Sensor and Magic Parts imported replacement— and miles ahead of the mass produced garbage iron used by Fender these days. That said, though, there will be very little difference between the Mercury and the Mojo/Heyboer. Save the $$ and put it towards the next build or upgrading some tooling/test equipment

 

[Chuck D. Bones]

When it comes to grounding in a power amp, the thing to think about is current. We DO NOT want large currents flowing in the chassis because those currents can cause unwanted feedback to the input stages, which causes motorboating and squealing. The best place to ground the secondary side of the output transformer is at the output jacks.

 

[Aquaticwombat]

I was gonna say I would ground it to the output jack, that's always been my standard practice building 5e3s. Incredibly easy amp to build if you don't mind cutting your hands to pieces on the chassis

 

[Fingolfen]

So I guess the operative question is why did MM set up the output like that. It looks as if the one lead is pre-soldered to the mount.

 

[analogdevice]

It was how Fender wired this transformer. The FTDO-59 is meant to be a close as replica of the original as possible. The FTDO-59S is a version of this transformer with a wire instead of the self lead.

 

[HamishR]

Yup - Self-lead means that the leads you use are the actual wire wound as the secondary. They haven't soldered an easier-to-solder lead to them as most transformers are made. The wire usually comes covered in a pink coating which is insulation for the windings. You scrape that pink stuff off the ends otherwise you can't solder it. As Chuck suggests I would recommend soldering the secondary connections to the output jack. Analogdevice beat me to it - In the original amps it was common to find the beginning of the secondary soldered to the OT frame. But they also grounded one end of the filaments which is not how I would build one today.

I can recommend the MM version - it sounds glorious, especially if you take the time to bias the amp properly. Mojo Transformers can be excellent too, but for an amp like this with so few components every part is super important for the sound. I have used both and prefer the MM. The Mojo isn't bad, and Heyboer can make an outstanding transformer, but in this case I use the MM.

FWIW I have tried the OT wired with the secondary grounded to the frame and can't say I noticed any additional noise or problems. I guess the connection is close enough to the output jack that it hasn't caused an issue, but I only tried that once and subsequently have always soldered directly to the output jack.