Separate heater circuits for individual tubes

[tdvt]

Laying out the power supply for the B-15 Pre project from this thread (LINK) & have been reading about elevated heaters, DC heaters, etc.

One of the things I came across mentioned separate heater supplies (individual heater PT) for individual pre-amp tubes to minimize noise (extreme case).

The PT I am using (Antek torroid) has two 6.3V (2A ea) taps & the circuit has just the two tubes (6SL7 & 12AU7). Also lots of references to noisy octal tubes, so I am wondering if there is any advantage to utilizing the two heater taps taps this way? Would it even be similar since both taps are from the same PT.

Vibrolax used the same PT in his SVT design but paralleled the two taps to one FWB/filter section & went DC.

One of the uses for this pre-amp would be to feed a recording console so I would like it to be extra quiet.

Worth the trouble?

[HotBluePlates]

... One of the things I came across mentioned separate heater supplies (individual heater PT) for individual pre-amp tubes to minimize noise (extreme case). ...

Do you have a link to that information?

The only thing I'm aware of which resembles that in any way is either a supply for preamp tubes with elevated cathode voltages (cathode follower, long-tail inverter, etc) which is referenced to a bigger-than-usual positive d.c. voltage, or a d.c. heater supply for preamp tubes.

... The PT I am using (Antek torroid) has two 6.3V (2A ea) taps & the circuit has just the two tubes (6SL7 & 12AU7). Also lots of references to noisy octal tubes, so I am wondering if there is any advantage to utilizing the two heater taps taps this way? ...

A heater winding for a 12AU7 and a separate one for a 6SL7 seems to me a silly and wasteful way to try to reduce noise. Especially since I repaired a (probably early-70's) printed circuit board B-15N, which is is probably the polar-opposite in terms of "great heater wiring" and it didn't seem noisy to me.

"Noisy octal tubes" related to heaters could simply be that the octals don't have a center-tapped heater like the 12A_7 series, so you don't have a chance to cancel hum potential inside the tube.

... Vibrolax used the same PT in his SVT design but paralleled the two taps to one FWB/filter section & went DC.

One of the uses for this pre-amp would be to feed a recording console so I would like it to be extra quiet. ...

D.C. heaters will do the best job of eliminating the risk of hum from heaters. And Vibrolax's information is much more sensible & trustworthy than what it sounds like you were reading for the individual a.c. heater wiring (but I did want to see the original source to make sure I didn't misunderstand the intent).

[vibrolax]

People have had mixed results with DC heaters, probably for the same reason that they have variable results with AC heaters.  A lot of different factors affect the noise floor.  I have had good results with both AC and DC heaters.  The SVT preamp was the quietest one I've built to date, and it has regulated 12 VDC heaters.

I don't believe you quite understand how my filament supply was designed.  The 2 x 6.3 VAC filament windings were connected in series (not parallel) to give 12.6 VAC.  This was rectified, filtered, and regulated to 12 VDC.  The filament supply "reference voltage" is also raised to 1/4 the B+ voltage to avoid exceeding the heater-cathode voltage limits for the cathode follower stages.

Here is the layout of the SVT preamp power supply:http://www.frontiernet.net/~jff/SonOfSVPCL/Images/Visio-AmpegSVTPreamp_PowerSupply_26Aug2014.pdf

Here is my description of its design: http://www.frontiernet.net/~jff/SonOfSVPCL/DIYSVTBassPreamplifierPowerSupplies.html

If you're using 6.3 V filament tubes in your circuit, you won't be able to do exactly what I did.  You could do it if you used a 12SL7 instead.  It is not very practical to use the Antek 6.3 VAC filament windings to produce a regulated 6V filament supply, because a linear regulator requires a minimum DC input voltage several volts higher than the desired output voltage.  This excess voltage is lost by the rectifier diode forward voltage drops,  ripple in the capacitor filter, and transistor junction drops in the regulator.  It was not even easy to get 12 VDC regulated output with the Antek transformer.  I had to use low forward drop diodes, a low dropout regulator, and pretty large filter caps.

[tdvt]

Thank you both for your replies.

I can't find the snippet regarding a separate PT for V1 though I'm nearly sure I read it. It was one of those meandering internet paths that are easy to get lost on. Looked through my history but.......

I should add that I am NOT anticipating issues with heater noise. But I would not rule it out either & posted my question due to lots of small pieces of info (probably dangerous) & the fact that I have these two heater taps. 

Vibrolax, you are correct about my misunderstanding your power supply & didn't see the write-up (I appreciate the link). I was trying to follow it from the photos. I realized that you used a reference voltage from B+ but I didn't realize you were using 12V.

I would like to keep this as simple as I can while achieving the desired results. I was just exploring this aspect to see if there were advantages to be had with a little more effort.

Thanks, TD