filament question

[funkmeblue]

does it matter which order I wire the filaments? I usually run 6.3 volts to the power tubes first and then over to the preamp. In this particular build my "gain stage" is closer than the power tube. Is this done for noise purposes or just how things usually lay out? thanks and sorry for the stupid question

[Andy Le Blanc]

It matters if its a series string, the most noise prone are at the ground end.
I've heard that observing a consistent polarity even with ac helps.
Twist the ac fil. dress any how, there was a post here with a pict. of a linear
wire dress, dc i think. You can lay it on the chassis, fly over the rest of the dress,
or stick it in a corner, whatever way suits your practice.

[funkmeblue]

right on, thanks, was kind of what I figured. I think I have a plan now....oh and also.....what's the reasoning behind having a ground tap for 5 volt filament supplies? And is it possible to use "shielded" wire for filaments. I thought I seen this someplace.

[Structo]

The twisting of the heater wires cancels out the hum.
Most preamp tubes have spiral heater elements, sort of a humbucking design if you will.
So if you keep the ac wiring in phase, that is run the same wire to pin 9 of each tube and the same wire to pins 4 & 5 of each tube the noise floor is greatly reduced.

Phase isn't so important on power tubes but I believe every little thing helps.

As far as dressing, there is the Marshall method of laying the wires in the back corner of the chassis and the overhead way Fender has always done it.
Both work fine.

Some guys run straight heater rails or busses to the power tubes then twisted pairs to the preamp tubes.

But I don't think it matters which tubes get the wires first since they are all in parallel.

If you want to get real fancy you can do DC heaters but it is more expensive and the results, not all that better from what I gather.

Not sure what you mean by a ground tap on the 5v filament supplies.

The common heater voltage is 6.3 vac.
If you mean a center tap on the heater winding that is done for a voltage reference.
If your PT doesn't have a center tap you can create a virtual center tap by connecting a 100 ohm resistor from each wire to ground.

[funkmeblue]

I was refering to some hammond iron that has a center tap for the 5 volt, oh and was also wondering while I'm on this topic......cathode bias amp, the 6.3 volt center tap....should I connect this to the tube side of the bias resistor to elevate it above ground...is that right? thanks

[rfgordon]

On the Hammond with the center tapped 5V--You can't ground that center tap if you are using a tube rectifier. Because the HT is taken off of one of the filament taps, a grounded center tap will dump HT to ground through half of that winding. Bad things happen--I learned this the hard way!

[funkmeblue]

thanks for the heads up, so what is it's purpose? 2.5 volt filaments?

[rfgordon]

I suppose there are other things you can do with a 5V winding...

Ya ne znayo, tovarich....

[paulster]

Phase isn't so important on power tubes but I believe every little thing helps.

Actually, it can help provided you have a push-pull output stage.

If you retain the same relative polarity on both sides of the push-pull pair/quad then any noise that gets introduced by the heaters will be broadly similar on both sides. Since one side is inverted by the OT it will effectively cancel out in the OT.

The heater noise will be negligible anyway since the gain of the power tubes is pretty low and the grid voltages are pretty high, but if you've got a choice of wiring in a way that could benefit your noise floor I'd go for it.

[FYL]

thanks for the heads up, so what is it's purpose? 2.5 volt filaments?

Using the CT as a pulsed B+ tap point slightly lowers supply noise.

[funkmeblue]

pulsed b+tap? sounds like something I need! What about elevating the heaters with the bias resistor?

[FYL]

pulsed b+tap? sounds like something I need!

This is Pülsëd B+Täp, where all amps go to 13.

What about elevating the heaters with the bias resistor?

Can work.