5F11 transformer replacement question

[chikov]

Hello everyone. I am helping my friend to bring back to life a beautiful 1958 Vibrolux. Unfortunately the power transformer was shorted and I had to get the replacement from Antique electronic supply. The closest to mine I could find is a little bigger, so I will have to enlarge the hole in the chassis, but the owner is ok with it.
I have 2 questions. Based on the attached schematics, is it ok for me in the like manner to ground one of the green wires for the 6.3 v circuit and for the 50 V bias circuit. Second, the center tap on the 6.3 V secondary, should I just isolate it?
Thank you.

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[Roe]

No just wire the heating like its ordinarily done these days? Ground the middle tap/wire (yellow/green) and connect the two green wires to the tube sockets

[chikov]

Thank you for your reply. That helps. As I started working on it I realize that pilot light was connected to the ground with one terminal. I guess I will have to replace it with the socket that has two separate terminals, Or is there a way around it?

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[sluckey]

Thank you for your reply. That helps. As I started working on it I realize that pilot light was connected to the ground with one terminal. I guess I will have to replace it with the socket that has two separate terminals, Or is there a way around it?
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Look closely and you'll see that there are two isolated terminals on that socket. The 'shell' of the bayonet socket connector has an isolating bushing same as the tip of the socket. But the terminal has been rotated and soldered to the mounting bracket which is physically attached to chassis. All you have to do is remove the solder and rotate the 'shell connector tab around so it it not in contact with the mounting bracket. Then you can run two wires isolated wires to the lamp socket.

I know the newer balanced wiring scheme is considered an improvement over the older unbalanced scheme. But honestly, I would leave it just like it is. It works very well and the slight improvement with heater hum will only be a small improvement. You may not even be able to tell a difference. I have a '57 Harvard that I thought long and hard about this when I had to replace the PT. I finally just decided to let it be. No regrets and it keeps the tweed chassis tidier.

Oh yeah, I left the selenium rectifier in my amp too.

[chikov]

Thank you for your reply. I wired in the new transformer and the amp came to life! It sounds amazing as you all would suspect. I went to check the bias of the output tubes and found a strange thing. All the voltages were pulsating. The voltage drop across the OT was changing from 6 to 14 v and the plate one was pulsating from 375 to 390 VDC. Is it normal in early vibroluxes?

[sluckey]

Maybe the tremolo is turned on? If so, turn it off.

[ampdan]

Damn shame another nice original amp has been hacked...

[chikov]

No, the tremolo is completely off.
Sorry about “hacking it” but how else you can fix an amp that has a broken power transformer and filter caps are covered with bubbles?

[Charlie Wilson]

You use a transformer that fits the chassis without altering it. The filter caps are not the issue.
CW

[Faze]

Sure does seem like the tremolo bias is pulsing. You measured the tremolo biases? I can’t think of anything else that would cause that that symptom.

[Mark]

I'd either get the original transformer rewound or use the Mercury transformer. I have found getting original transformer rewound cheaper.

[Seiche]

Unfortunately the power transformer was shorted and I had to get the replacement from Antique electronic supply. The closest to mine I could find is a little bigger, so I will have to enlarge the hole in the chassis, but the owner is ok with it.

How is that even considered an acceptable option for a repair of a rare $3000+ vintage amp?

[Mark]

Agreed, I wouldn't be happy if a direct replacement was available.