new 5e3 build blowing fuse

[Danelectron]

I've just finished building a 5e3 and I'm blowing the main fuse. I powered up the chassis with no tubes installed to check voltages, but the fuse blew instantly. I'm not getting any shorts to ground from the windings. No shorts between any of the windings. Primary winding resistance read 2.9 Ohms. Secondary red 330-0-330 winding read 120.8 Ohms (63.8 ohms and 58 ohms respectively to center tap). Secondary yellow 5v read .4 Ohms and the secondary green 6.3v read .3 Ohms. The power cable coming into the amp was made up as follows. White (neut) to white on PT primary, Black (120v) to fuse, then to on/off sw., then to black primary on PT. The B+ from pin 8 of the rectifier socket was isolated from the circuit by the standby switch. I removed the PT primary black from the main switch and was able to measure 120v through the fuse and power switch. What am I missing?

[loudthud]

Is there a center tap for the 6.3V or 5V windings? If there is one for the 5V (usually yellow with black stripe), don't ground it, cut it off and put some heat shrink over the end. If there is one for the 6.3V (usually green with yellow stripe), disconnect it from ground and ohm from one of the other 6.3V wires to ground, it should be infinite ohms.

[Danelectron]

Is there a center tap for the 6.3V or 5V windings? If there is one for the 5V (usually yellow with black stripe), don't ground it, cut it off and put some heat shrink over the end. If there is one for the 6.3V (usually green with yellow stripe), disconnect it from ground and ohm from one of the other 6.3V wires to ground, it should be infinite ohms.

This is a 41316. It has a bias tap that I insulated off. I am getting infinite resistance to ground on all windings. I haven't wired the artificial CT for the 6.3 winding yet. Would that make a difference? I am going to disconnect all the secondaries and see if the fuse will hold. This doesn't make any sense. I must be missing something, but I have looked this over and am stumped. Thanks for your attention. Maybe I have a goblin there goblin up my electrons.

[Danelectron]

I just hooked up the artificial tap on the 6.3 winding and the fuse held, but the wiring insulation instantly started toasting. I shut it down. There is no lamp in the lamp socket. I measured resistance across the lamp socket and it is 0.4 Ohms. I cut the lamp socket out of the circuit and the tube sockets now read clear and the lamp is still shorted. What a piece of crap socket. I may be able to save the transformer by reinsulating the leads. I will be replacing the lamp socket. I guess I didn't recognized the short because the 6.3v winding would read near zero lead to lead. The artificial tap provided enough resistance to allow the fuse to hold. What an experience.

[Danelectron]

Question. Is the transformer winding insulation tougher than the lead out insulation? I'm concerned that I may have taken some milage off the filament winding.

[Danelectron]

I replaced the lamp socket with a vintage style and it's up and running fine. Power transformer is fine so far. Thanks.