Heater Winding/Center Tap Question

[davidb]

I just saw a post from an amp tech talking about how he replaces most center taps with virtual center taps, especially in vintage amps with expensive PTs. The logic here is that if a short between pins 2+3 occurs, it will burn out the PT. I have a Sunn and a Laney that use center taps and I want to preserve them as best I can, is it worth making this modification? I also have a Music Man that grounds one of the 6.3V windings, and I think it would be worth converting this as well since the same problem could occur.

Thanks for the help, I’m still learning here and appreciate the input.

David

[Esquirefreak]

Can't you just fuse the CT if you're worried?

/Max

[pdf64]

Protecting things with a fast acting HT fuse will mitigate numerous failure modes, including this one.
Bear in mind that if the heater circuit gets pulled up to anode voltage, eg by the pin 2 to 3 short described, the heater to cathode insulation of all valves in the amp is likely to be damaged.
I think better mitigation for a pin2 to 3 short by ensuring the integrity of the OT secondary circuit would also a good way forward. eg use of dedicated output sockets for each tap rather than a load impedance selector switch, safety resistor hardwired across the OT secondary in case all else fails.

[HotBluePlates]

... The logic here is that if a short between pins 2+3 occurs, it will burn out the PT. ...

In my limited experience, this doesn't happen.

I had a power tube short Pin 2 to Pin 3, and it popped the mains fuse instantly when I turned on the Power switch.  New fuse, new tube, and the amp was 100% again.

We are not protecting the heater winding, because its thicker wires support more current than the high voltage winding.  And the high voltage winding already has a mains fuse to pop in the case of excessive current draw.