Power Transformer confusion Fender Prosonic

[Mr_bibbles]

Hey y'all,

Ive done a few transformer swaps in my day but something about this one is confuzzling me. I think it's because it has a dual primary? But we can hook the together to ensure the correct 120V at primary, producing good voltages at secondary?

Prosonic Schematic: https://www.thetubestore.com/lib/the...-Schematic.pdf



Using these two guides, how should I hook up the primaries? I'm assuming that I can wire the two primaries in parallell?

Green / Black ---> Yellow/black?
Red / black Primary 1 IN Black Primary 2 IN? (power inlines)

I am almost certain this is incorrect but confused on the labeling for the MM transformer.

Thanks all!

[g1]

Sounds right. Two 0V tied together, two 120V tied together.

[mozz]

I would think resistances would be close also. What is the violet wire? Shield?

[Greg Robinson]

The Mercury Magentics drawing is either incorrect, or they've manufactured the transformer without the thermal fuse.
Note on the Fender schematic, hot goes through the power switch, a glass fuse, then an NTC thermistor (inrush limiter), then connects to the purple lead of the transformer, which connects to the one of the primary windings through a thermal fuse (EDIT: which is internal to the transformer, if that was unclear) - the two semi-circles are a schematic symbol for a thermal fuse. The start of the winding that the thermal fuse is connected to is brought back outside the transformer on the black/red lead, so that if the windings are paralleled for 100/110/120V operation, the thermal fuse will cut both windings, not just one.

100V wiring:
Black/red to black/yellow (terminal BK/RD? Been a while since I've been inside a Prosonic, don't remember exactly how the internal wiring is arranged, probably the classic Fender Faston terminal dance)
Black/green to black (terminal 1)
White to neutral (terminal M2)
White/black floating (terminal 2)

110V wiring:
Black/red to black/yellow (terminal BK/RD)
Black/green to black (terminal 1)
White floating (terminal 2)
White/black to neutral (terminal M2)

120V wiring:
Black/red to black/yellow (terminal BK/RD)
Black/green to black and neutral (terminal M2)
White floating (terminal 1)
White/black floating (terminal 2)

220V wiring:
Black/red floating (terminal BK/RD)
Black/green to black/yellow (terminal 1)
White to neutral (terminal M2)
White/black floating (terminal 2)
Black floating (terminal 3)

230V wiring:
Black/red floating (terminal BK/RD)
Black/green to black/yellow (terminal 1)
White floating (terminal 2)
White/black to neutral (terminal M2)
Black floating (terminal 3)

240V wiring:
Black/red floating (terminal BK/RD)
Black/green to black/yellow (terminal 1)
White floating (terminal 2)
White/black floating (terminal 3)
Black to neutral (terminal M2)

Hope that helps.

[g1]

The Mercury Magentics drawing is either incorrect, or they've manufactured the transformer without the thermal fuse.
Note on the Fender schematic, hot goes through the power switch, a glass fuse, then an NTC thermistor (inrush limiter), then connects to the purple lead of the transformer, which connects to the one of the primary windings through a thermal fuse - the two semi-circles are a schematic symbol for a thermal fuse. The start of the winding that the thermal fuse is connected to is brought back outside the transformer on the black/red lead, so that if the windings are paralleled for 100/110/120V operation, the thermal fuse will cut both windings, not just one.

Is it possible that the violet in the MM drawing is the same as the Fender purple, and they just don't show the thermal fuse?
In which case, hot from thermistor should go to violet, and other wiring as per 1st post?

[The Dude]

If purple is shield (although not drawn that way), it would be easy enough to tell with a quick continuity test.

[Greg Robinson]

Is it possible that the violet in the MM drawing is the same as the Fender purple, and they just don't show the thermal fuse?
In which case, hot from thermistor should go to violet, and other wiring as per 1st post?

Yep, exactly as I said, either the drawing is wrong, or if their drawing reflects reality, then it's been manufactured wrong. One way to find out would be to ask them, but in my experience Mercury never give a straight answer, so you'd be stuck with testing for yourself.

And yes, wired per O/P, but make sure the hot line goes to the purple/violet lead.

[Mr_bibbles]

Thank you all, especially Greg for your extremely detailed post. I'll let you know if I die in a horrible explosion, otherwise assume it works great!

[Enzo]

Use your light bulb limiter.

[Mr_bibbles]

Use your light bulb limiter.

Yessir, always do in these situations, gunna pull all the tubes and test gently on power up.

When I sat down to do the work, I noticed that there is conflicting information here;

A couple times its been stated that the "OP's Wiring is correct":

(Green / Black ---> Yellow/black?
Red / black Primary 1 IN Black Primary 2 IN? (power inline)


But in your post Greg you suggest the following:

120V wiring:
Black/red to black/yellow (terminal BK/RD)
Black/green to black and neutral (terminal M2)
White floating (terminal 1)
White/black floating (terminal 2)

As of right now, the amplifier is wired (before getting to me) at per Greg's post above, and it is pulling LOTS of current through the bulb (on for a millisecond, then off until we figure it out).

I have the violet wire like this

BLACK 120VAC --> Switch --> Thermistor ---> Violet + YEL/BLK + RED/BLK

If this wiring is correct, I'll pull secondaries and test for shorts. This transformer came to me already installed (but blowing fuses), definite possibility of damage to the rest of the amp.

[g1]

BLACK 120VAC --> Switch --> Thermistor ---> Violet + YEL/BLK + RED/BLK

Thermistor to violet only. Blk/Yel and Blk/Red tied together.

[Mr_bibbles]

Thermistor to violet only. Blk/Yel and Blk/Red tied together.

Ah, I was using a continuity meter which showed them connected, although it's possible it's a false reading from inside the transformer. I'll flip the board and be sure. If this is the correct wiring though, the amplifier is pulling a LOT of current so something else must be wrong.

[Helmholtz]

For a short (!) test you may use one of the primaries only, i.e. just leave the Yel/Black and Black wires connected and watch input current.

[Mr_bibbles]

For a short (!) test you may use one of the primaries only, i.e. just leave the Yel/Black and Black wires connected and watch input current.

I am still very confused on this after trying it a couple ways. I wired it up per Greg's suggestion:

"120V wiring:
Black/red to black/yellow (terminal BK/RD)
Black/green to black and neutral (terminal M2)
White floating (terminal 1)
White/black floating (terminal 2)"

BLK HOT ---> Thermistor ----> Violet ---(internally connected to...BK/RED)

BK/RED --> BLK/YEL in "BK/RED" Terminal (floating)

BK --> BK/GRN tied together with NEUTRAL at M2

Light bulb limiter VERY bright for a milisecond before turning off. Disconnected secondaries to check for false positive, still lighting up, no AC on secondaries.

So I tried it like this;


BLK HOT ---> Thermistor ----> Violet ---(internally connected to...BK/RED)

BLACK RED/BLACK (BLK?RED TERMINAL)

YEL/BLK + GRN/BK +Neutral

And I am getting good voltage through the transformer, but with each multi meter lead hooked into the B+ secondaries (Both Secondaries Floating, hooked to ONLY 1 multi meter lead each) I am getting close to 700VAC reading on the Multimeter. Is this normal, just doubled because the secondaries are not hooked into the supply? Or is it way too high and I am wired in series not parallel?

[The Dude]

Well, the transformer diagram in post one shows a 364-0-364 transformer, so your reading is approximately what I'd expect from red to red secondary leads.