Identifying Power Transformer leads for FENDER Amp

[czech-one-2]

Hi folks, hopefully somebody here can point me in the right direction.
I bought a 'project' Fender Musicmaster Bass Amp amp that has a blown power transformer. Since this amp is definitely not in 'collectable' condition I'm going to set it up to run 6L6 tubes. I just received suitable power and output transformers but I need to insure that I hook it up the PT correctly.
I'll include images of the new PT and the color codes/layout of the MMB PT in a layout diagram.
I know this should be easy but I want to be 100% certain that I hook it up correctly.
The original Fender PT has:
2 green heater wires
1 white wire [Primary]
2 red wires
1 red/yellow wire
1 black wire

I have one extra wire on the new PT [PHOTO] and I'd like to know which wires correspond to the Fender color codes and which wire would be capped off.

http://i.imgur.com/nY1FKTo.png

[czech-one-2]

I'm assuming:
1] the two red wires are the same on both transformers. [350V]
2] the new white wire is the same [Primary] as the old white wire and would connect to the AC line on the layout. I would cap off the other white wire. [does it matter which white wire is capped off?]
3] the two green wires are definitely the same heater wires.
4] that leaves the two brown wires. One would replace the old black wire, one would replace the old red/yellow wire
Is this correct?

[Justin Thomas]

The best way to find out is to ohm out the different wires and see what's connected to what. Do you have a multimeter?

Justin

Edit: the two brown wires are a bias tap. Seems the Musicmaster Bass is cathode-biased. Now, you have an option. You'll also have to use a full-wave bridge rectifier, since the high-voltage secondary seems to not have a center tap...

[czech-one-2]

I do, but was hoping that comparing the layout drawing with the values/codes on the new transformer would be obvious. I'm a guitar player not a tech so 'obvious' doesn't apply here.
I just want to avoid a 4th of July fireworks show in June.

[czech-one-2]

Oh no, you mean this PT won't work in my amp without extensive modification? I guess I ordered the wrong PT, although the seller assured me it was correct.I don't want to change the amp from being cathode bias..

[Justin Thomas]

That's easy enough - you don't HAVE to use the bias tap. Just tape the ends off separately and tuck them away. Don't cut them off, they might come in handy later. You WILL have to use a bridge rectifier, though - others can advise on how to implement that. But basically, Ampeg used them in their "budget" amps like the Mercury, Rocket, etc. 4 diodes instead of two, wired a bit different. If you find guts shots, you can wrap the diodes into a neat little bundle.

But yes, you can use this one.

Justin

[czech-one-2]

Thanks Justin, I'm just not sure how to proceed. I just wanted a drop in replacement. This forum helped me troubleshoot my other amp, so I guess it would be possible with some major assistance from some very patient forum members. But I'm not sure if I should just try to return the PT at this point....

[Justin Thomas]

If there truly is a drop-in available, go for it. But check first, and check thoroughly before returning it. Honestly, I don't know why a Blackface Champ/Princeton (not Reverb) PT shouldn't work; you shouldn't have to add a center tap then. You'd only have to tape off the tube rectifier heater windings.

But if you were able to troubleshoot & repair your other amp with help from here, you can tackle this...

Justin

[jmaf]

That transformer will not work for 6V6 tubes, the +B voltage is too high.

The red-red would have to be around 250 VAC maximum.

Find attached the correct specs for the transformer you need.

40-18100.pdf

[czech-one-2]

That transformer will not work for 6V6 tubes, the +B voltage is too high.

The red-red would have to be around 250 VAC maximum.

Find attached the correct specs for the transformer you need.

[ATTACH]39450[/ATTACH]

Right, I was going to use a pair of RCA 6L6's that I have sitting in a drawer.
I do have this in a parts drawer but I'm not sure if its the correct part for this [It's 1000v /10A]...or how to wire it up.
[IMG][/IMG]

[Enzo]

The original Fender transformer had two red wires for the high voltage, but they had one VERY important extra wire, the red/yellow wire. That is the center tap which gets grounded. Your new transformer does not have a center tap, so if you wire the red wires to the diodes like the old one, nothing will result - no high voltage supply. In other words, it won;t work.

The old transformer had a black and a white for primary wires. Your new one has two whites. The two brown wires on the new are your bias WINDING, not a bias tap. If you don;t want a bias supply, and prefer cathode bias, simply do not wire the browns to anything.

The label on the new part clearly shows the wiring.

As others mentioned, you would need to use a full wave bridge to make the high voltage work.

[czech-one-2]

Hi Enzo, that clears up the black/white original wires, they are both white on the new PT.
I'm clear on the green 6.3v wires.
The red wires are the same hi voltage wires.
Its not clear to me how to wire up a full wave bridge rectifier. Is my part suitable? And what replaces the missing center tap wire?
I'm unclear on what is better, not using the brown wires and staying cathode bias, or using the brown bias winding wires? Pros and cons?

[Enzo]

Cathode bias or fixed bias. neither is "better", they are just different. What is better, lager or pilsner?

The missing center tap is replaced by grounding the negative corner of your bridge rectifier. Look up bridge rectification.

[jmaf]

Its not clear to me how to wire up a full wave bridge rectifier. Is my part suitable? And what replaces the missing center tap wire? I'm unclear on what is better, not using the brown wires and staying cathode bias, or using the brown bias winding wires? Pros and cons?

Your part is suitable. There are 2 corners labeled AC. The red wires go to those.

The minus corner goes to ground, the plus corner is now your positive high voltage.

Look at the capacitors on your power supply, do they handle 500 VDC? You need 500 V rated caps for the higher +B, the 300 VDC ones no longer do the job for this transformer.

Just isolate the bias taps, you won't use them. Keep the cathode bias, it's gonna self regulate using 6L6's and it'll probably sound great.

[czech-one-2]

Thats easy....Pilsner!