Technical Question about SE

[kagliostro]

If I've understand well the principal difference between SE and PP is that there is any cancellation of noise in an SE OT

Always we talk about reducing Humm (that sometime is at level that results pesky) adding filtering on B+ path

What I would like to know is:

If we have done all the possible on filtering B+ and assuming there are no problems related to wire path on the chassis

Is heater supply to be considered the principal source of Humming ?

How do you consider to feed filaments with DC instead of AC ?

Will DC reduce more the Humm than an elevated heart with AC ?

Will DC reduce more the Humm than an elevated heart with AC in junction with a real or artificial CT ?

Swap from AC 6.3V to DC is feasible starting from the same 6.3V AC winding (if there is enough AC current disposable to compensate the loss in DC) ?

Many Thanks

Franco

[pdf64]

I think that if valve heaters are wound humbucking, and the heater - cathode insulation is perfect, and the lead dress is good, then AC heaters referenced to 0V common should be fine.

Heater circuit elevation mitigates for valves with imperfect heater - cathode insulation.

DC heating mitigates for non spiral wound heaters and lead dress issues.

[Williamblake]

On a sidenote there actually once was humbucking in SE OT by having a small tap on the primary. It was used a lot in european radios. Also it prevents OT saturation a little.
Current enters at yellow in the drawing.

[kagliostro]

Many Thanks pdf64 & Williamblake

@ pdf64

I forgot to indicate the real or artificial CT, thanks for remembering it to me

DC heating mitigates for non spiral wound heaters ........

Oh, so it depends also by the tube quality

Non spiral wound heaters are a construction defect or some tube are wound deliberately that way ?

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@ Williamblake

The two OT I salvaged with the PT has the additional Tap for G2, and I'll use that connection





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The PT I salvaged (from a Graetz Stereo radio) that I want to use for a small Stereo Guitar Amp (VOX AC4 + VOX AC4TV) with the 6.3V winding feed (on the radio) a load of 3665mA

in the Stereo Amp I'm planning, the heater consumption is 2320mA, I know that if I rectify I loss current (from 1000mA AC to ~600 or 700mA DC if I'm right) do you think that starting from 6.3V 3665mA I can cover the consumption of 2320mA in DC ???

At the moment I want to use on the amp AC on heaters, but I'm collectin documentation in the event I've problems (and also for personal knowledge)

Many Thanks

Franco

[pdf64]

On a sidenote there actually once was humbucking in SE OT by having a small tap on the primary. It was used a lot in european radios. Also it prevents OT saturation a little.
Current enters at yellow in the drawing.

Rest of that schematic? I’m wondering what the green primary leg connects to.

[Williamblake]

There you go. On another sidenote i wonder why some pictures in this forum are shown with a wrong height to width ratio ...

[sluckey]

I've seen that a lot in smaller powered comsumer amps such as found in '60s console stereos (RCA, Zenith, etc). I just always considered that OT has a tap that is used as a filter choke for the rest of the amp.

[HotBluePlates]

... noise in an SE OT ... we talk about reducing Humm ... adding filtering on B+ path

What I would like to know is:

If we have done all the possible on filtering B+ ...

I don't know what you mean by "all the possible filtering."

That said, look at what Fender did in their earlier amps (which they made worse in later amps).  In particular, look at where the OT is connected to the power supply.

The 2nd stage of a power supply is much cleaner than the 1st stage.  Sourcing OT voltage at that 2nd node will solve most single-ended hum problems.

[kagliostro]

Ciao HBP

Thanks for answering and Many thanks for the suggestion about the second node

I don't know what you mean by "all the possible filtering."

I meant this:

The idea is to leave the AC4 and the AC4TV PS as original and to add something like this before, to feed the two PS



For B+ something more of that is difficult that I can think 

So I'm looking to what I can do more for filament supply

I'm not a great fan of DC heaters (unless it's a PCB mounted amplifier)

But if necessary .......


EDIT: Here is a first approach to the Layout, the added PS Board will be positioned between the two Boards




Franco

[shooter]

.... if you have way too many caps 

[kagliostro]

Ciao Shooter

 

Franco