dc heaters again..

[giorgio]

Hi everybody,I know this is an old story,but...I built a very nice sounding Trainwreck express clone,with toneslut transformer.The output transformer is buzzing,I suspect the chassis transfer the vibration to the tubes,so I have an almost loud hum..Before I try to suspend the transformer with some rubber,or even substitute it,I'd like to try dc heaters,just experimenting and excluding the possibility of noisy ac heaters(due to the layout I suspended the heater twisted wiring Over the valves,like Dumble did,but not so good,I suppose!!).The question is:I have a center tap for heaters output from power transformer,3 12ax7 and 2 el34,how can I rectify 6,3 ac to dc???

[Daedalus]

This worked for me:
You have to fine tune the dropping resistor to get the right voltage.

[defaced]

Can't say I've ever seen a heater supply with an inductor in it. Honestly, I'd just stick with a rectifier bridge, some caps, and some way of dropping the voltage down to ~6.3v.

[Enzo]

Let alone 20,000uf of filter cap.

When you are tracking down hum, you need to realize ther are many sources of hum and each has its own solution. It is not one monolithic problem that can be slowly eroded away the more solutions you throw at it.

In tube preamps, AC heated filaments CAN SOMETIMES couple to the nearby cathode. If electrons flow from filament to cathode, then some 60Hz hum can be in troduced. If we make the heaters more positive than the cathode, the the electrons will not be attracted to the cathode. That is the reason we sometimes elevaste the AC heater supply to some DC level above ground. Alternatively, if we run the heaters on DC there is no 60Hz to introduce, even if the cathode is more positive than the heater.

The point to keep in mind though is that making the heaters DC or raising the AC to some DC level above ground ONLY affects this heater/cathode source of hum. It will have zero effect on power sup0ply ripple in the B+, zero effect on vibrating output transformers, zero effect against ground hum, and so on.

If your regular AC heaters are not making hum in an amp, doing these measures will have zero effect on the other types of hum. If your transformer is buzzing, this won;t help it.

When you say the output tranformer is vibrating, are you sure it isn;t the power transformer? In either case, I doubt the vibration is what ios making hum in your amp. And if it is, DC heaters will have no effect on it.