What causes this?

[496dart]

I dont think the wire gauge would have anything to do with it,if the wire were to thin it would burn up.You did say you tried a different set of power tubes,right?If some internal element was shorting to your heater element in the power tube,I am pretty sure it would blow a fuse,never seen it do otherwise,just wondering if for some reason your power tubes are drawing more than their rated 6 amps,this would be very odd if they did,so the likely hood of two different sets of tubes exhibiting this oddity would be slim to none.I know we've been all over this but just give another check to be sure nothing is connected to that heater supply that shouldnt be.It doesnt make sense that they would understate the amps on that heater,but the odds of getting 3 trannies in a row that have the same problem is unusual,and the only other possibility is that the heater does not actually have a 7amp rating.It is fine with just the preamp tubes,so the aux tranny will work.Just make sure you get at least a 7amp and 10 would be better.Let us know if you need any help getting it wired in.Pretty basic,your primaries hook up just like the main one to the switch,one to the fuse,and the secondary goes to the power tubes heaters.Just be sure to seperate the pre from the power tubes heaters.

Yes-i tried 2 quads of tubes.
so i go through the same fuse as the original tranny ? or do i need to add a fuse?
i ordered a 6.3v / 8a

[stokes]

Adding another fuse wouldnt be a bad idea,although you should be okay with the fuse thats in there.You are not adding any more current than would be there with all the tubes on the same heater.The 8amp tranny should be fine.

[496dart]

Update--

I installed the aux trans today. Heaters look great now. 6.3v on the power tubes. 6.5 on the pre tubes.
Now i have a new problem. A Very loud HUM. You cant hear it with the master volume off. Im sure its the new trans causing it. I made sure the fil. wires were twisted tight . Ive poked around with the amp on, moving wires around, the hum doesnt change ..

[stokes]

Do you have a center tap on the aux tranny?Is it connected to ground?If so it is most likely the placement in relation to the OT.If it isnt oriented correctly you are getting magnetic coupling from the aux to the OT,which is just what it sounds like since you get the hum with the volume turned off.What you will have to do is take the mounting screws out of the aux. and with the amp on turn the transformer until the hum goes away and mount it in that position.If it is too close to the OT you may have to move it further away from the OT.

[496dart]

No CT on this one.
There really isnt any other way to mount this one . See pic...Its next to the PT.

http://img.photobucket.com/albums/v2...IMG00001-2.jpg

the trans is a Hammond 266N12

[Enzo]

If there is no CT, then do the pair of 100 ohm to ground from either side of the winding. Fender did this on thousands of amps over the years.

[stokes]

Looks like that is the only thing you can do.Thought we went over the 100 ohm artificial CT earlier,should clear up the hum.

[496dart]

tried the 100 ohms. I only have 2 resistors here , so i tried it on each trans seperately. No change . Unless i have to have a pair on each trans... ?

[stokes]

As long as you have the CT on the heaters from the main tranny connected to ground,now thats the heater CT not the yellow high voltage CT,you just put one 100 ohm resistor from each side of the aux tranny.If you have these 100 ohms connected correctly and you still get a lot of hum,you are going to have to find another location for that aux tranny.The fact that you get the hum with the volume down all the way leads me to believe you are getting magnetic coupling from the aux to your OT.Could also be being picked up from being too close to the power tube.

[stokes]

Another thought,make sure your heater connections are connected in "phase".Pin 2 to pin 2 and pin 7 to pin 7 on the power tubes,and likewise on the preamp tubes,4&5 to 4&5 and 9 to 9.Crossing these will induce hum.

[496dart]

As long as you have the CT on the heaters from the main tranny connected to ground,now thats the heater CT not the yellow high voltage CT,you just put one 100 ohm resistor from each side of the aux tranny.If you have these 100 ohms connected correctly and you still get a lot of hum,you are going to have to find another location for that aux tranny.The fact that you get the hum with the volume down all the way leads me to believe you are getting magnetic coupling from the aux to your OT.Could also be being picked up from being too close to the power tube.

NO, I DO NOT get hum with the master volume turned off .

I will check the phase today

[stokes]

Sorry,I just re-read the old post,memory is the first to go when you get old,in that case having the 100 ohm resistors and CT on the main FT grounded properly,the next step would be the phase.If all the sockets are okay,try switching the leads on the new heater tranny.

[496dart]

tried swapping those on both trans. (one at a time) No help on the hum.

[496dart]

There isnt anywhere else to move the aux tranny. I doubt i can get a smaller one. Im about to just pull the new PT out and send it back, we know its over-rated . Im sure they would give me a refund. I would just have to order one from somewhere else -and a different brand obviously .

[stokes]

If you checked everything covered here,I guess that would be your best bet.That PT is definately not hefty enough for the heaters they claim it will handle.