Vibro-Champ Power Cord

[C Moore]

Want to put a 3 prong cord on our 1972. Do I just follow th existing 2 prong layout?
Black to center of fuse.
White to on/off switch.
Green to chassis ground.
Leave the power transformer wires where they are.
Remove the "death cap" and do not replace it.
Thank You

[Phil_S]

Want to put a 3 prong cord on our 1972. Do I just follow th existing 2 prong layout?
Black to center of fuse.
White to on/off switch.
Green to chassis ground.
Leave the power transformer wires where they are.
Remove the "death cap" and do not replace it.
Thank You

I would do it this way, assuming your are in USA.

Black from the wall supply is hot. That goes to the fuse and then the switch. From the switch, there should be a wire to one side of the PT primary.

White from the wall supply (assuming a SPST on the hot), goes directly to the other wire on the PT primary. If you are using a DPST, then, of course, the switch will interrupt this connection.

Green (redundant neutral) goes to a dedicated bolt running through the chassis as close as practical to the entry point. Solder a ring lug to the wire. Some people use a bolt on the PT; while generally OK, it is not best practice.

Yes, clip the death cap.

Which side of the fuse holder to wire to the wall supply? There are two different kinds. The safe practice is to wire it so the connection to the fuse is interrupted when you remove the cap. Think this through. You don't want a shock when you pull the fuse. If you have the kind where the fuse cap makes the connection, then wire the wall supply to the side lug. If you have the kind of fuse cap that grips the fuse and pulls it out, you might want to wire the wall supply to the end lug, but be sure it operates as you intend.

[C Moore]

Thanks for the help, I am almost home with this. But I do not know which of the wires is the PT primary. As the pictures show, Red and Yellow/Black from PT to fuse, Black and Black/Green from PT to one lug of switch. Which wire gets the White Neutral of the new cord.
Thanks

[Phil_S]

I didn't look at your pictures until just now. Maybe I'm not seeing it right, but I think that PT is wired wrong. There are a whole pile of wires on the fuse that don't belong there. Look at the attached, 2nd page is the layout. If this is a stock PT, colors should match. Typically, black is primary, yellow is 5v, green is 6.3v, red is B+, striped wire of similar color is usually center tap and is grounded.

On this particular layout the green 6.3v is grounded to the chassis on one leg and the other leg supplies 6.3v to the pilot and tube filaments. Not the best way to do it, but I suppose it works.

My money is on the black wires as the primary. IMO, you've got some fixing to do. Did this amp work OK before you started the 3-prong cord? I'm guessing it didn't work.

In working with any grounds to the chassis, leave as much naked wire as you can, so you are able to use that chassis ground point. You won't be able to resolder to the chassis without a 100W iron or gun.

[Phil_S]

A second thought...you've got "extra" wires on this PT. This should be sorted out before you start moving stuff around. It might be an international PT with extra primary to permit 240v hookup. Let's start with the question of whether you received it in working condition. Also, what country was it last known to operate in?

Lets look for a date code on the PT. This would be a 6 or 7 digit number. Post any numbers you see on the PT or a clear picture of them.

[C Moore]

Oh Boy -
Just got the amp. Don't know if it passed signal. All I ever did was plug it into a speaker cab for about 2 minutes. There were no sparks, flames, hot spots; the fuse did not blow. It all seemed fine so I started a "cap job" and the cord replacement. Do not know if it was ever intended for a foreign country. Didn't those Fenders have a Red Switch of some sort on the back of the chassis? Anyway...
PT# 010020
CSA Test
606 307 1 7 (this number is hard to read, so this is a guess)

OT# 022905
606124

Serial# A30460

Ink stamp in chassis:
Torres
Sep 21 1971
Yes you are right regarding the layout. I downloaded that same layout so I could do the 3 prong cord. When nothing matched, I figured I was just reading it wrong so I started asking for help.

Thanks Again

[Phil_S]

PT 606 307 1 7 (this number is hard to read, so this is a guess)
OT 606124
Ink stamp in chassis: Torres Sep 21 1971

I asked for these in an attempt to determine if the PT is original or a replacement. 606=Woodward Schumacher, the maker 3= 1973 (one must guess at the decade, Torres stamp is a good reference), 07 is the week (February). This might be a replacement, see below. (In the interest of full disclosure, I am an amateur builder and not an amp tech.)

It might be that the date code is non standard and is actually 30-71, that would be July or August 1971, meaning this could well be an original part.

The OT appears to be original, made in June 1971, which predates the Torres assembly stamp.

Neither of the part numbers match the schematic, but dates and manufacturer are appropriate. Let's assume for now that you have the correct PT for this amp, and try to figure out the wiring. That's plan A.

Plan B is to buy one of these PT325H here http://www.musicalpowersupplies.com/4.html or some other suitable replacement that doesn't cost an arm and a leg. Unless it's blown, I don't expect we'll need plan B.

There are many wires emerging from the PT. Let's eliminate what looks correct: the red pair and the yellow pair that go the rectifier look right, the green filament supply wires look right. the red/yellow center tap (to the red pair) looks right.

I don't know what the orange wire to ground is. Possibly the high voltage winding (red pair) is a split winding and the red/yellow represents one inner leg, and the orange represents the other inner leg, meaning you join them both at the ground to have a continuous winding. I'm guessing based on the existing wiring and we may have to do some testing to figure this out. Let's leave it for now and discuss the primary hookup, which is your original question.

I think we need to gather more info. What I'm thinking here is that we've got an export tranny and whoever installed wisely it took advantage of the configuration to maximize the VA capacity of it by taking a split winding and wiring it in parallel. (Series wiring would be for 240V input.) In other words, the existing wiring suggests there are two primaries: black-red/black and black to yellow/black. I see one of the black wires is really black/green, which is what's leading me in this direction. If both were solid black, I would be headed another way.

Sorry for being long winded...to the simple test. With no tubes and the correct fuse, power it up. Use the existing cord unless it is unsafe (cracked, cut, etc.) Use your DMM to check all the output voltages on the secondaries. Test the 5V winding and the high voltage winding at the rectifier socket -- just check for AC voltage on 2&7 (5V) and 4&6 (~630V expected). If you get anywhere near the expected readings, assume the existing wiring is correct. If not I will help you test further to untangle things.

If it checks out, follow the existing wiring. It looks like there is a hole in the chassis near the entry point of the power cord. That will do double duty very nicely. Run a screw into it and first terminate the green redundant ground from the power cord there, using a ring terminal that's been soldered to the green wire. Then see if you can find a screw down cord clamp to make a secondary retainer and stress relief for the power cord. Chances are only 50-50 you can re-use the existing stress relief and you may end up replacing it with a rubber grommet. You can use a zip tie on each side of the grommet as the retainer if you must, or tie a knot on the inside and use a zip tie outside. Under no circumstances should the entry hole be only bare metal as that creates the risk of slicing the cord, making the chassis live.

Do let me know if this works out.

[C Moore]

Once Again, thanks for all of the help so far. Will report back ASA I have something conclusive. Hopefully that will be tomorrow.

[CaseyJones]

That's an international or "export" PT, many Vibros came with them. It's wired for the U.S. as you see it. It can be set up for 240 volt mains.

I didn't look at your pictures until just now. Maybe I'm not seeing it right, but I think that PT is wired wrong. There are a whole pile of wires on the fuse that don't belong there. Look at the attached, 2nd page is the layout. If this is a stock PT, colors should match. Typically, black is primary, yellow is 5v, green is 6.3v, red is B+, striped wire of similar color is usually center tap and is grounded.

On this particular layout the green 6.3v is grounded to the chassis on one leg and the other leg supplies 6.3v to the pilot and tube filaments. Not the best way to do it, but I suppose it works.

My money is on the black wires as the primary. IMO, you've got some fixing to do. Did this amp work OK before you started the 3-prong cord? I'm guessing it didn't work.

Don't be an alamist, that's my job.

[Phil_S]

That's an international or "export" PT, many Vibros came with them. It's wired for the U.S. as you see it. It can be set up for 240 volt mains.

Yes, I realized this, but I am too long winded and buried it as a possiblity in a subsequent post. Thank you for clarifying, as I was not sure.

[angelodp]

Old post, but I have the same PT ( for VibroChamp build ) and was wondering. As I read you say that its set up for 120v so on the primary side

YB and RB are joined and at the fuse

GB and B are joined and at the switch.

Question can I use the green lead that is grounded to create a twisted pair for the heaters. I would also use two 100ohm resistors for a faux center tap to ground off of the connection the green wires make at the light.

I buzzed the orange wire and it does not appear to be connected to anything?? What is that for.

[Phil_S]

YB + RB and GB + B are arranged to run the dual primary windings in parallel. This correct for 120V provides for the full power available. Note, I did not verify any of this. I'm assuming it is already wired for 120V.

What's wrong by modern standards is switch, which belongs on the hot leg along with the fuse. The fuse should sit on the hot (+) wall supply between the wall plug and the amp so that the wall supply sees the fuse immediately when you plug in the power cord. The switch should break the hot (+) connection between fuse and the PT. This protects your house first and your amp second. The switch or the fuse on the cold (neutral) is worthless if there is a line fault and the fuse doesn't blow.

If the 6.3v winding is two green wires and one is grounded, then, yes, you can and probably should rewire as a twisted pair with the faux CT.

The single orange wire, if it doesn't connect to anything is probably the frame ground. Just check it to ground with your meter while the PT is energized to make sure there is no voltage on it.

[angelodp]

Thanks Phil, I will set up that switch and fuse per modern specs. Strange about that orange wire though? It does not show up on any schematics I am found and it does n to buzz to anything, including ground…. although it was set up originally to ground.

Hang on found this…. anyone else needs this info.

http://bmamps.com/Schematics/fender/vib ... _ab764.pdf

Thanks

Ange

[martin manning]

The orange is usually an electrostatic shield between primary and secondary. I'd just ground it.

[angelodp]

Thanks Martin.