Power Transformer 6.3V Secondary Center Tap....

[acorkos]

I am working on a 1964 Fender Super Reverb, and among other problems, I discovered the filament heater secondary center tap wire has burned through the cloth insulation, and the center tap wire has broken near the exit hole on the transformer.

Is this transformer still safe to use if I cut away this filament heater center tap and create an artificial center tap, connecting two 100 ohm resistors from the secondary windings to ground?

[52 Bill]

As long as there are no connections to the case, yes you can still use the transformer.

You can also remove the bottom cover from the transformer and replace the center tap wire with a new one. Most Fender transformers were permafilled, so you will not be able to connect directly to the winding, but you will be able to get to the end of the burned lead wire. This way you will also be able to inspect the interior of the tranny for damage.

[pdf64]

That transformer is really old and has got really hot. I'd want to put it on to a 'hi pot' high voltage insulation tester (eg at least 1000V ac, not the dc type), and check between all windings, to each other and to the body, before connecting it to a line supply.
Do the insulation test to the OT and choke also, as the current will that burned the wire will have had to flow through one of them too.
There might be shorted turns in the OT primary from the heat, the geofex test will pick those up.
http://www.geofex.com/FX_images/xform_test.gif
Check all wiring around the power tubes and the power tube sockets for burnt contacts (or just replace the sockets).
If all ok, then try the 100 resistor artificial center tap.
But ensure that the amp has a grounded line cable, and check that the line outlets on the wall are grounded properly.

Alternatively, just replace all the iron.
A significant part of the amp's value will be tied to them. So take them out, replace with modern ones which will be far safer and reliable, and keep the originals somewhere safe and dry.

[Tom Phillips]

In my experience the 6.3V CT wire is a smaller gauge than the main 6.3 V winding so it fails like a fuse when a tube shorts HV to heater and the actual heater winding is OK. I have never had a return due to a failed transformer when I insulated the remaining CT stub and installed an artificial resistive CT circuit. I choose not to reconnect the CT with a new wire because I feel that the remaining part of the wire inside the PT may have been compromised. Having said that, if you are worried about lawyers getting involved you could explain the situation to the customer and replace the PT. Sad but true.
Tom