AC heater question.

Greetings to all.

In my mic preamplifier, I decided to make a 6.3 V AC.
There is a significant low-frequency hum in the sound.
I tried to fix it in different ways - 3.15v - 0 - 3.15v, resistors 100 ohms (artificial mean point).
This only partially removes the rumble, but it still remains.

Next I tried to ground the 6.3V capacitors and the rumble completely disappeared ...
I have a question, is there something wrong with this method (for example, the hum was gone and the noise increased)?

It probably should not do that to begin with. Heater windings throw a lot of current around. So it is important that the two wires are twisted together so that the magnetic fields from the currents cancel each other out. They don't have to be tightly twisted. Just enough to minimize loops. Also they should not run near any other sensitive circuitry. Ideally they should be tucked into the corner of the chassis edge if possible or taped (not conductive or it will make a shorted turn) to the chassis to keep them out of the way. When they come out to get to a tube, each wire should double back in itself to maintain the field canceling.

Also, keep heater wires as far away as possible from any high impedance / high gain inputs. If they run anywhere near the the first gain stage (twisted or not), it could definitely pick up heater hum.

I would leave the two 100 ohm to ground just to keep the voltage from floating around although it probably doesn't matter. And the caps are probably fine two. The output impedance of that winding is going to be really low so some small caps are ok (although I am a little surprised they do anything with low frequency hum - I would think small caps like that would be for high frequency fizzle). Just make sure these components-to-ground connect to a ground point back near the power supply chassis connection using a separate wire. If you inadvertantly connected them to another point you would effectively be dumping whatever noise you're filtering into the that ground point which again could be amplified and heard.

I've had better luck with a pot... 250 ohm iirc ....instead of the resistor...  still had other issues like wiring and bad ground scheme though.....

scott2000 said:

I've had better luck with a pot... 250 ohm iirc

Click to expand...

Same here.  The pot, and proper lead dress that squarewave described, are about the extent of my knowledge about reducing heater hum though.

i see no problem using the caps if they work,

don't know why they work, as they have about 250 K AC resistance and you are using them on a circuit that has around 6.3/ amp (maybe) = 6 ohms,

I always come back to this page when i have a heater issue.
http://www.valvewizard.co.uk/heater.html

I myself am surprised that this works ...
My preamp is REDD47.
I previously had DC Heater, but I decided to experiment with AC.
With the capacitors turned out as if it works DC (I listen in the headphones).

This scheme I once saw on the Internet and decided to try this option.
I tried different value for capacitors, still the same result - low-frequency rumble disappears.

I'm not very strong in the theory of radio electronics, so I had this question - maybe the rumble was gone, and with it the modes of the lamps were violated and the sound might somehow get worse, noise, etc., but maybe everything is in order ...

mrclunk said:

I always come back to this page when i have a heater issue.
http://www.valvewizard.co.uk/heater.html

Click to expand...

Me too, I used it recently. I had a tube that was causing me some AC hum faintly but it was audible and that just vexes me after all the cost and time of a nice build. The issue followed the tube and the fake CT/elevated heater method fixed it. Much better to use some resistors I had laying around than start hunting for a more quiet tube.

The thing I've never had good luck with is running DC heaters in series. As in stringing several tube filaments in series. It was a bit of a PITA to get the voltage requirements right from the filament transformer.

I got some free time and I decided to continue my experiments with AC Heater.
Low-frequency rumble disappears the same way with one capacitor instead of two.
Why does this work?

vmanj said:

Why does this work?

Click to expand...

It works because the heater wires have a reference to ground. If they didn't have this reference to ground, they can be at a high AC voltage, because they are capacitively coupled to the HT windings, so may end up floating at several hundred volts AC. The parasitic capacitance between the HT and heater windings is a few hundred pF, so, in order to clamp the leak to ground, it takes a much lower impedance between the heater winding and ground, for example a 100nF cap will have about 100 times smaller impedance than the parasitic, reducing the leakage from let's say 100V to only 1V. Instead of a cap to ground, it could be a resistor; at 50/60Hz, the parasitic capacitance's leakage impedance is about 1 Megohm, so a 100 ohms resistor attenuates the leakage by a factor 10 000. I don't understand why it didn't work for you; are you sure you wired it correctly?
Now, what's the difference between the one-cap and the two cap solutions?
The one-cap solution works by reducing the leakage voltage, but the two-cap works better because it balances the voltage, i.e. at any moment there is as much negative voltage as positive, so that cancels out. Actually some imperfections make the balance not perfect, so the result is never 100% clean. In addition the two-cap solution actually filter out the high frequency dirt that comes from the line.

Thank you.

Unfortunately, with 100 ohm resistors, my hum does not completely disappear, but with the capacitor everything works fine.
And with one capacitor sound seemed to me more "open", and with two capacitors - more "compressed". But it's possible it just seems to me.

https://www.google.com/search?q=emi+redd.47&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj6j8Oe7eHaAhVjDJoKHbySDqwQ_AUICigB&biw=1280&bih=669#imgrc=XviuPsKLG1koFM:

On this photo REDD.47, it seems 4pin 1 EF86 connects to 5pin E88CC, and 5pin EF86 connects to 4pin E88CC.
Is it necessary to connect the heater of several vacuum tubes equally - 4-4, 5-5, or does it make any difference ?

vmanj said:

Thank you.

Unfortunately, with 100 ohm resistors, my hum does not completely disappear, but with the capacitor everything works fine.

Click to expand...

That suggests the AC heater voltage is quite corrupt, containing significant higher harmonics.

On this photo REDD.47, it seems 4pin 1 EF86 connects to 5pin E88CC, and 5pin EF86 connects to 4pin E88CC.
Is it necessary to connect the heater of several vacuum tubes equally - 4-4, 5-5, or does it make any difference ?

Click to expand...

No difference; the constitution of various tubes is so diverse it does not really matter.

Thank you.

My transformer is toroidal and on it is another winding for 6X4 - 275V-0-275V, can this be the cause of damage and the occurrence of these high harmonics on AC 6.3V?
By the way, the heating of the 6X4 is also connected in parallel to the EF86 and E88CC, maybe this, too, as it brings harm to 6.3V ...

So, if I do not connect the capacitor, then immediately after turning on and then there is some unpleasant sound in the lamp itself E88CC. I tried to replace the tube, still this "ZZZ" remains ...

vmanj said:

My transformer is toroidal and on it is another winding for 6X4 - 275V-0-275V, can this be the cause of damage and the occurrence of these high harmonics on AC 6.3V?
By the way, the heating of the 6X4 is also connected in parallel to the EF86 and E88CC, maybe this, too, as it brings harm to 6.3V ...

Click to expand...

Do you mean you use only the 6.3V winding, or do you also use the HT winding for rectification and B+?
Rectification is what creates the harmonics. They can be somewhat decreased by placing a capacitor across the secondary, typically 0.1uF. Caution: very high voltage. The cap must be rated at least at 600Vac.

No, I only use one 0.1 uF capacitor connected to one of the AC 6.3V wires, the other capacitor wire is connected to ground and everything ... it works!

I just thought that the winding 275-0-275 maybe somehow destroys the AC 6.3V and creates high harmonics in my 6.3V heater?

Here is my scheme.