5F2A "Tweed Princeton" Build Question

[Razzle Dazzle]

Hi Guys

I got a quick question about my 5F2A build...

I want to build the amp after the TubeAmpDoctor kit, but with better components (Jupiter caps, turret board & Mercury Magnetics transformers) but a couple things are different with the tranformer cable layout and I am a little unsure if I did everything correct!

I attached a picture of the TAD layout + transformer specs and my layout + Mercury Magnetics transformer specs, could y'all please double check if all of the wiring on my layout is correct? I'm pretty sure it should be good but I rather ask before I do something stupid...

TAD Layout:

TAD Transformers:

My Layout:

Mercury Magnetics Transformers:

 

[CB91710]

I am curious why TAD connected the unused line taps to the rectifier pins 3 and 5.
They are unused on the tube, so I guess they are simply anchoring them there rather than insulating the ends and tying them back.
Personally, I'd do that, rather than anchor them to the tube socket.

Other than that, the only difference I see is that you have an 8ohm output transformer, and the TAD drawing is using the 4 ohm tap from a 4-8-16 ohm unit, and I don't see where your grounded side of the OT secondary (Self Lead?) is grounded.

You could also add a switch to swap between the 230v and 240v primary taps on the PT... using the 240 will reduce your high voltage slightly and knock off some of the headroom for a little more dirt (brown sound?)

Note that on the Fender drawings, it shows both pins 1 and 2 of the 6V6 grounded... don't do that (and you didn't), pin 2 is a filament lead and the original drawings did not use the false center tap. Leo just grounded one side of the 6.3v secondary.

 

[Razzle Dazzle]

I am curious why TAD connected the unused line taps to the rectifier pins 3 and 5.
They are unused on the tube, so I guess they are simply anchoring them there rather than insulating the ends and tying them back.
Personally, I'd do that, rather than anchor them to the tube socket.

Other than that, the only difference I see is that you have an 8ohm output transformer, and the TAD drawing is using the 4 ohm tap from a 4-8-16 ohm unit, and I don't see where your grounded side of the OT secondary (Self Lead?) is grounded.

You could also add a switch to swap between the 230v and 240v primary taps on the PT... using the 240 will reduce your high voltage slightly and knock off some of the headroom for a little more dirt (brown sound?)

Note that on the Fender drawings, it shows both pins 1 and 2 of the 6V6 grounded... don't do that (and you didn't), pin 2 is a filament lead and the original drawings did not use the false center tap. Leo just grounded one side of the 6.3v secondary.

Yeah the OT has a self lead!

The Mercury Magnetics PT only has a 240V primary taps, but the trick with the switch is a nice idea! Will save it for another build...

 

[CB91710]

Oh crap... I crossed that up thinking you were using the TAD PT.
So the "self lead" is already grounded to the frame? I'm not familiar with the term.

 

[Soul Tramp]

I am curious why TAD connected the unused line taps to the rectifier pins 3 and 5.
They are unused on the tube, so I guess they are simply anchoring them there rather than insulating the ends and tying them back.
Personally, I'd do that, rather than anchor them to the tube socket.

Yeah, that's kind of weird. Technically not a problem, but not something I wouldn't do. It could create confusion in the future. I feel tube sockets are somewhat sacred and shouldn't be used for misc. wire/component anchor points (except for grid/screen resistors). I've seen builds where resistor & caps are soldered to unused tube pins . It's just sloppy/lazy design & construction.

it's sort of like not grounding pin 1 on a 6L6 amp and saying you can swap the 6L6 with an EL34. Bad idea!

 

[Razzle Dazzle]

Oh crap... I crossed that up thinking you were using the TAD PT.
So the "self lead" is already grounded to the frame? I'm not familiar with the term.

Yeah the self lead is connected/grounded to the frame of the OT. It's more vintage accurate since the early Fender amps had that feature as well...

 

[Razzle Dazzle]

I just got the last part in the mail, a Carling 2BK62-63 but I am a little confused on how I need to wire it!

It only has a "2" marking on the bottom and nothing on the sides or top...

Could someone please help me out?

 

[Razzle Dazzle]

Also...

Is a 1A slow blow fuse ok for this?

 

[CB91710]

Confirm with your meter. The switch is a souble-pole single throw, so the hot would likely go on one side and the neutral on the other.

1a slow blow is fine.
Fender was all over the place using anything from 3/4a to 2a on similar amps with a single 6V6.
The current Mojotone kit specs a 1a slow-blow for the 5F2-A

 

[Razzle Dazzle]

Confirm with your meter. The switch is a souble-pole single throw, so the hot would likely go on one side and the neutral on the other.

View attachment 624807




1a slow blow is fine.
Fender was all over the place using anything from 3/4a to 2a on similar amps with a single 6V6.
The current Mojotone kit specs a 1a slow-blow for the 5F2-A

Thx! I'm getting 1A slow blow fuses in that case...

Would this be correct? Twisted wires are the outlet cord, the other blue is from the transformer and the black as well (connected over the fuse)...

 

[CB91710]

That's the correct wiring, but be sure to verify which contacts actually make/break. If the orientation of the contacts is rotated, you'll be applying a direct short (with no fuse) across the mains.

 

[Razzle Dazzle]

I got another question...

On the TAD Layout the resistors that connect to the lamp holder are are connected to ground as well via a soldering strip that is screwed to the chassis, which I am missing, but on their product photo the resistors are connected to ground only, via the soldering strip that is screwed to the chassis, but not to the top part of the resistor/capacitor combo...

Which one is correct?

 

[Razzle Dazzle]

That's the correct wiring, but be sure to verify which contacts actually make/break. If the orientation of the contacts is rotated, you'll be applying a direct short (with no fuse) across the mains.

Ok that sounds scary!

I do not actually know which contacts actually make/break since nothing is marked on the switch.

Could you please help me out on that?

I'm good with soldering and putting things together but I am not the best with electrical theory...

 

[CB91710]

I got another question...

On the TAD Layout the resistors that connect to the lamp holder are are connected to ground as well via a soldering strip that is screwed to the chassis, which I am missing, but on their product photo the resistors are connected to ground only, via the soldering strip that is screwed to the chassis, but not to the top part of the resistor/capacitor combo...

Which one is correct?

View attachment 624815

View attachment 624816

The two are the same. The wiring layout doesn't show the screw, but the center lug on the terminal strip is the same piece of metal as the screwed-down connection.
The schematic will simply show it to the common ground from the filter caps on the board.

There may be a jumper between the center and top lugs that is not visible in the photo.

Ok that sounds scary!

I do not actually know which contacts actually make/break since nothing is marked on the switch.

Could you please help me out on that?

I'm good with soldering and putting things together but I am not the best with electrical theory...

Unless someone else is familiar with those Carling switches, you'll have to check with your meter.

Put one probe of your meter on one of the terminals (any of them) and put the other probe on the one right next to it.
Listen for the meter to show continuity, and operate the toggle.
It will be wired like one of the two examples.

For the top one, both connections from the power cable go on one end, and the other end goes to the fuse and PT.
For the bottom one, the power cable goes on one *side* and the other side goes to the fuse and PT.

 

[Razzle Dazzle]

The two are the same. The wiring layout doesn't show the screw, but the center lug on the terminal strip is the same piece of metal as the screwed-down connection.
The schematic will simply show it to the common ground from the filter caps on the board.

There may be a jumper between the center and top lugs that is not visible in the photo.

...

So this should be correct? I added a pink wire from the bottom of the resistors to a chassis ground...

 

[CB91710]

Here's the Mojotone layout:
Their switch may or may not match your Carling

 

[Razzle Dazzle]

...

Unless someone else is familiar with those Carling switches, you'll have to check with your meter.

View attachment 624819

Put one probe of your meter on one of the terminals (any of them) and put the other probe on the one right next to it.
Listen for the meter to show continuity, and operate the toggle.
It will be wired like one of the two examples.

For the top one, both connections from the power cable go on one end, and the other end goes to the fuse and PT.
For the bottom one, the power cable goes on one *side* and the other side goes to the fuse and PT.

Ok I just tried this and the Carling switch that I got is the upper example...

Does it matter if neutral or hot from the power cord connect to the blue (tranny, 240V) or black (fuse, 0V) or is it irrelevant which one connects to which?

 

[Razzle Dazzle]

Here's the Mojotone layout:
Their switch may or may not match your Carling


View attachment 624826

So does that mean my layout (with the pink wire) is correct or should I connect the resistors directly to ground and not to the top part of the resistor/capacitor combo as well?

I'm not good enough with these things to see off the Mojotone if mine is correct now...

Here is the TAD schematic (which I can't read), if that is any help...

 

[CB91710]

Ok I just tried this and the Carling switch that I got is the upper example...

Does it matter if neutral or hot from the power cord connect to the blue (tranny, 240V) or black (fuse, 0V) or is it irrelevant which one connects to which?

It's not *that* important, but good practice to connect the neutral to the transformer's "common", which would be the black on yours.

 

[Razzle Dazzle]

It's not *that* important, but good practice to connect the neutral to the transformer's "common", which would be the black on yours.

Ok good, I will do that then!

Thank you so much for all your help CB91710...